Beyond Brawn by Stuart McRobert

• An average or even less-than-average potential for bodybuilding, if achieved, is stunning to an untrained person, and respected by almost any trained individual.
• Achieving your potential for muscle and might demands extraordinary discipline and dedication. There’s no place for half measures, corner cutting, laziness or lukewarm enthusiasm. If you don’t train well, rest well, sleep well, and eat well, you’ll get nowhere or make only minimal progress.
• You have tremendous control over your physique development, if only you would start to employ it.
• Negative thoughts and negative people will harm all your endeavours. If you imagine failure, dwell on it, and prepare for it, you’ll fail.
• With a good plan, and no time for negativity, you’re set for the confidence and persistence that lead to success. But the journey there will be neither trouble free nor easy.
• Lifting weights is a solo activity over which you alone have the power of control. Once you know what to do, you need rely on no one.
• Never lock yourself into using an exercise if it doesn’t suit you. The number one priority for any exercise is that it does you no harm.
• Don’t focus on what you’ll never be able to do well. Instead, focus on what you can do better.
• Use a rep count for a given exercise that best suits you, get as strong as you can in exercises that suit you and which you can perform safely, keep your body fat levels to below 15% (or below 10% if you want an appearance that’s stunning--assuming that you have some muscle), eat healthfully, perform cardio work, stretch regularly, and then you’ll have the full bodybuilding package.
• Experience has taught me that the conservative approach isn’t just the safest way, it’s the most productive and satisfying over the long term.
• Most people train too much. Not only is this counterproductive for short-term results, it produces the overtraining that wears the body down and causes long-term structural problems.
• The biggest exercises are uncomfortable when done with effort. If they were easy to work hard on, they would do little or nothing for you. But don’t use an exercise that’s harmful for you.
• In this book, “light” weight generally means that the set’s rep target can be met easily, with little or no strain. A “heavy” weight is one that demands much effort to complete the set’s rep target regardless of how many reps that is.
• One of the biggest and most disastrous errors in the training world today is the belief that basics-first abbreviated programs are only for beginners.
• Bodybuilding and strength training are almost laughably simple; but simple doesn’t mean easy. All that really matters is focus, and progressive poundages in correct form.
• Pick a handful of the biggest and best exercises for you and then devote years to getting stronger, and then stronger still in them.
• There’s even danger in using variety because you can lose focus and get caught up in an excessive assortment of exercises.
• Focus on the big basic lifts and their variations. Do this for most of your training time. Don’t try to build yourself up using tools of detail.
• You can’t get very powerful in the key basic exercises without becoming impressive throughout your physique.
• Never train if you don’t feel systemically rested from your previous workout. While some local soreness may remain, you should be systemically rested, and mentally raring to go for every workout. If in doubt, train less often.
• Once-a-week training for the biggest exercises is a good rule of thumb. Fine-tune your training frequency according to your individual recovery ability.
• Unless you walk every morning feeling fully rested, and without having to be awoken, you’re not getting enough sleep. And even if you are making gains in the gym, more rest and sleep could substantially increase your gains.
• Add small poundage increments when you’re training full-bore. Don’t go short-circuiting a cycle by adding a minimum of 5 pounds to eh bar at a shot. Get some pairs of little discs.
• Dependable training for typical people with regular lives is about doing things slowly, safely, steadily and surely. It’s not about trying to do in two months something that needs half a year.
• What matters is what works. If you can gain only from a routine that’s absurd in its brevity and simplicity by conventional standards, fine. But if you can gain well using a routine that most hardgainers wouldn’t gain an ounce on, that’s fine too.
• High reps, especially in thigh and back work, have been proven to pack on loads of muscle.
• Don’t neglect your calves, abdominals, grip, or the external rotators of your shoulders. This accessory work matters.
• Some neck work is mandatory if you’re involved in contact sport, and still a good idea if you’re not. And back extensions will help keep your lower back in good order.
• Once you have a good grasp of training, all you need is persistence and time. Then the realization of your potential for muscles and might is almost guaranteed.
• There’s not much if anything that’s really new in the training world. What’s “new” is usually just a twist on an old idea.
• With a dose of creative lingo and modern-day advertising hoopla, even something that has been around for decades can appear new.
• The dip, done in correct form, is a terrific exercise that’s much underused. It’s at least as productive as the bench press.
• Never, ever let your attention waver from progressive poundages in correct form. Never, that is, until you no longer want to build stronger and bigger muscles.
• Only you can find how far you can go by actually going as far as you can go.
• Urging realistic expectations doesn’t mean accepting mediocrity.
• Age isn’t the limiting factor untrained people usually make it out to be. The limiting factor is in the mind. Expect little from your body and that’s what it will deliver. Expect a lot from it and that’s what it will deliver.
• Never pile on bodyweight by adopting a long-term very-heavy eating program. You want a muscular physique, not a soft or flabby one.
• Once you can strictly press overhead a barbell weighing the equivalent of your bodyweight, you’ll be a better presser than nearly all weight trainees.
• What matters the most to you is your progress, and comparing yourself with yourself. Everything you study and apply related to training should be geared to this.
• You must have a great passion for what you’re doing if you’re to be successful at it. If you try to achieve at something that your heart isn’t really into, and that your body doesn’t respond to, you won’t get far.
• Your immediate short-term target should be to take the next small step towards your next set of medium-term goals.
• Never lose sight of the pivotal importance of progression. Organize your training program, nutrition, sleep, and rest habits so that you make progression a reality.
• To realize your potential, you need to become an achievement-oriented, goal-driven and success-obtaining individual.
• Achievement comes in small steps, but lots of them. Lots of little bits add up to huge achievement.
• Success is rarely an accident in any endeavour. Success in the gym is never a hit or miss activity. It’s planned.
• Deadlines are often imperative for making people take action, in all areas of life.
• Giving something a deadline and urgency, and it usually gets done.
• There’s nothing like the urgency of concentrating on a specific goal by a specific deadline to focus attention, application, and resolve. Without something specific to rally attention and resources, people tend to drift along and never get even close to realizing their potential.
• Avoid getting locked into tunnel vision that keeps you looking at the same sort of targets throughout your training life.
• If you want to be successful in achieving your potential you need to program that success. Step leaving life to chance.
• Achievement in any sphere of life depends on getting the individual moments freight, at least most of the time.
• An essential part of the organization needed to get each workout day right is a training diary. At its most basic this is a written record of reps and poundage for every work set you do, and an evaluation of each workout so that you can stay alert to warning signs of overtraining.
• It’s not enough just to train hard. You need to train hard with a target to beat in every work set you do. The targets to beat in any given workout are your achievements the previous time you performed that same routine/workout.
• Unless you have accurate records of the achievements to be bettered, you can’t be sure that you really are giving your all.
• Most trainees have neither the organization needed for success, nor the will and desire to push themselves very hard when the need to.
• Never become dependent on another person to get in a good workout.
• Effective training has to be intensive, and intensive training is very difficult to deliver on a consistent basis without a demanding taskmaster to urge you to deliver.
• Treat workouts as very serious working time. Get down to business and keep your training partner or supervisor at a distance. Keep your mind focused rigidly on your training.
• Always be able to train well by yourself. Have spells where you intentionally train by yourself, to be sure you can still deliver the goods alone.
• Take as much control over your life as you can. Learn from your mistakes. Capitalize on the good things you’ve done. Do more of the positive things you’re already doing, and fewere of the negative things.
• Any equipment other than the basics nearly always serves to divert attention from where most application should be given.
• Spoil trainees for choice, and you’ll spoil their progress too.
• Supplements will never be the answer to training problems.
• Until you get the basic package of training, food, sleep, and rest in general, to deliver good steady gains in muscle and might, forget about any fine-tuning with supplements.
• Ignore anything and anyone that will hinder your progress. You are in charge of your training. Never surrender that authority to others.
• The advantages you get from a home gym are so profuse and profound that, if you’re serious about training, you should do your utmost to get one.
• Parallel-grip bent-legged deadlifts, plus chins and dips, cover most of the body’s musculature. Just those three exercise, if worked progressively and for long enough, can produce a lot of muscles.
• If you have to load or unload a heavy barbell that rests on the floor, lift the end up and slip a disc underneath the inside plate. The raised end will make plate changing much easier.
• If it’s training day today, and so long as you feel well recovered from your previous workout, train today.
• Use a belt very selectively--for low-rep squats and deadlifts, and overhead presses--or not at all. Otherwise, you’ll become dependent on it to generate the necessary intra-abdominal pressure you need to protect your spinal column during heavy lifting; and without that armor you’ll be a shadow of your usual self.
• Successful weight training in its various forms is about progressive resistance. Despite this being so obviously central to training, it’s implications so often go ignored or only barely noticed. Successful training is about making lots of small bits of progress, with all the bits adding up to huge improvement. To achieve this you must have persistence galore, patience in abundance, and revel in knocking off each little bit of accumulation. Concentrate on knocking off one little bit at a time, and long-term success almost takes care of itself.
• As always, your barometer of progress is poundage progression. If the poundage gains aren’t coming, cut back your training volume by reducing total sets and/or exercises, and perhaps by training less frequently. Less work but harder work, and less total demand upon your recuperative abilities, will usually get the poundage progression back on track.
• If you’re gaining in your core exercises for a given cycle, you’ll be gaining in size and strength generally. The core movements are what you need to focus on as the cycle gets ever heavier and more demanding, and closes in on its end.
• The secondary exercises should not restrict progress in the core movements when you’re focusing on building mass. [...] In practice, to maximize gains on your core exercises, you may need to phase out some of the secondary movements as you approach the end of a cycle, or reduce their training frequency.
• Continue with the slow poundage increments, and progress will continue to feel smooth, good, and strong.
• While it’s essential to add poundage to the bar as often as possible, it’s imperative not to be enslaved by it.
• The greatest number of consecutive full-bore workouts is no good if you’re not recovering fully from each of them.
• Don’t be fullhardy, or else you may regret it later. Back off and come back next week for a hard workout when you’re ready. This aspect of conservatism especially applies once you’re in your thirties, and older.
• Remember, safety first, at all times. Patience, conservatism, and training longevity will serve you best over the long term. Haste and shortcuts invariable backfire. Haste makes waste.
• When adding poundage to the bar, use smaller rather than larger increments.
• Don’t ruin the potential magic of abbreviated routines by adding poundage too quickly, in too large jumps, or by training too frequently.
• Find the time to develop a flexible body and then maintain it.
• Eventually you will reach the point where no progress is being made, or is forthcoming. This represents the end of the cycle for that exercise.
• Conservatism, with few exceptions, is the way to go for most people who lift weights.
• Make haste slowly.
• The harder you train, the less training (volume and frequency) you need to stimulate strength and increase muscular growth.
• As you gain experience of training hard, you’ll learn to tolerate more discomfort.
• A steady diet of extremely heavy weights imposes enormous stress on the body. To pre-exhaust will reduce the size of the poundage needed in the compound movement to deliver a good training effect.
• Training intensity is a means to an end, not the end in itself.
• Training intensity is a fundamental and irreplaceable component of making muscle growth and progressive poundages a reality, but that’s all.
• Whatever you try, never persist with something that doesn’t help to keep your training poundages moving up, no matter how much it may be promoted by others.
• Don’t assume that anyone who claims to be a qualified personal trainer really knows what he’s doing. Strings of letters that indicate certifications of various organizations, or degrees obtained, don’t necessarily signify competence as a coach.
• Potentially, the square may be the most productive single exercise you can do provided you can perform it safely and progressively. The more efficiently you squat, the greater the potential benefits you can extract from it.
• Mastering the squat, and then intensively and progressively squatting on a consistent basis is a linchpin of successful bodybuilding and strength training. Don’t miss out on your chance to exploit this wonderful exercise.
• If you can’t squat safely and productively using a barbell, you should try both the hip-belt squat, and the parallel-grip deadlift.
• The parallel-grip deadlift isn’t just an alternative to the barbell squat. It’s an excellent exercise in its own right.
• Some form of deadlifting should be part of every program.
• If you don’t barbell squat you must find an alternative that at least approaches the quality of the squat. If you don’t barbell squat, you should parallel-grip deadlift, hip-belt squat, or leg press, along with some form of deadlifting for the latter two exercises.
• If you don’t find a good alternative to the barbell squat you’ll greatly reduce the potential value of your training for building muscle, if not almost extinguish it.
• Shrugs done face-down on a bench set at about 45-degrees work the musculature of the upper back differently to the regular standing shrug. In the incline shrug the whole upper back is involved, especially the lower and middle areas of the traps, and the muscles around and between the shoulder blades.
• The incline shrug in particular will help improve posture for people who have rounded shoulders.
• The parallel bar dip works more muscle than does the bench press.
• The developmental effects of the bench press in your particular case should also be a consideration in exercise selection. If you find that you get overly heavy lower pecs from the bench press (or dip), the incline press should be a preferred choice.
• There are seven small areas that shouldn’t be neglected during the focus on the core movements. This support seven can have a big impact for keeping you free of injuries. It’s made up of specific work for your calves, grip, shoulders external rotators, neck, midsection, lower back (work from back extensions additional to that from deadlift variations), and finger extensors (to balance the strength of opposing muscles in your forearms). The leg curl should be included too, to provide hamstring work additional to that given by deadlift variations. And the lateral raise is a valuable isolation exercise, to help produce healthy shoulders.
• Deadlifting using a thick barbell provides tremendous grip work. Add the thick-bar deadlift to your deadlift day’s work, either on top of your regular work if you recuperate well, or instead of a little of your regular work, in order to keep the total volume of work constant.
• Most bodybuilders and strength trainers perform their reps too quickly.
• Perform each rep as an individual unit that ends with a brief pause prior to performing the next rep. Take the time you need to set yourself to perform the next rep perfectly.
• Abbreviated training is the most productive type of training for typical drug-free trainees. The potential effectiveness of abbreviated training rests on the brevity of its routines and its infrequent workout frequency relative to conventional training methods.
• Particularly in the pre-steroids era, working out three times a week with a full-body program was the standard.
• The incline shrug is the best all-purpose upper-back shrug.
• If your training poundages are moving up steadily, and your form is consistently good, you’re bang on course. To be able to gain like this you may not need to train any exercise more often than once every five to seven days. And there are some people who may be better off training some of their exercises and body parts less often than once a week.
• Most people weight train too frequently, and don’t provide enough time for their bodies to grow stronger and bigger. Thus they fail to progress; and in addition they accumulate wear-and-tear injuries because their bodies are being worn down.
• The more progressive workouts you put in, the faster your overall progress will be. But if you train too frequently you’ll not be able to produce many if any progressive workouts.
• It’s a dedication to results that counts most, not a dedication to mere gym attendance.
• Don’t weight train if you’re still dragging your feet from the previous workout.
• Results from your weight training come from using incrementally ever-greater poundages. To achieve progressive training poundages you must rest between workouts long enough to recover from the impact of each workout, and then rest a bit longer so that your body can build a smidgen of extra strength and muscle.
• Successful weight training is about stringing together as many progressive workouts as possible. Twenty progressive workouts over ten weeks will produce far better results than thirty workouts over the same period but with only a handful of them being progressive.
• Weight-training success is about results, not just about how many hours you clock up at a gym.
• Experiment with training frequency to see what delivers steady exercise poundage gains for you. This will be relative to your individual recovery ability and the type of training program you use.
• A good training program that doesn’t yield good results can often be made productive by supplying more rest, sleep, and nutrition.
• “Best” is defined as what consistently produces poundage gain on all your exercises.
• Twenty-rep rest-pause squatting and deadlifting are extremely demanding, which is why they can be extremely productive, but only when combined with a very abbreviated training program, lots of recovery time, and plenty of quality nourishment.
• Single-rep work is exaggerate rest-pause training where the pause between reps is extended to several minutes, making the individual reps into sets of one rep each.
• Remember, many if not most people don’t have the robustness of joints and connective tissue needed to prosper on singles.
• Choose exercises you can safely perform over the long term.
• Once you’ve found your preferred major core exercises, stick with them over the long term. It’s a fallacy that you must regularly change your exercises in order to keep progressing. Changing your exercises around excessively is even counterproductive because it stops you from applying yourself to a given group of exercises for long enough to really milk them dry and make sufficient progress in strength to yield a difference.
• Rather than look for a better way to train, look for ways to recover better between workouts, and to focus better during your workouts so that you can train harder and with better form.
• Training each exercises just once a week doesn't necessarily mean training each body part only once a week.
• Sleeping well on a regular basis is of critical importance. You need to take action to correct any sleeping inadequacies you may have. Otherwise your inability to sleep adequate will continue, your recovery will be compromised, and your rate of gain in muscle and might impaired.
• Unless you wake every morning feeling fully rested, and without having to be awoken, you’re not getting enough sleep. And even if you’re making gains in the gym, more sleep and rest in general could substantially increase your gains.
• Getting adequate sleep is pivotal for enabling your body to recover optimally from training. Most trainees shortchange themselves of sleep, and as a result restrict their rate of progress in the gym.
• Use chalk everywhere you need the help, especially in back exercises and upper-body pressing movements.
• A flexible body helps protect you from injury so long as you don’t perform your stretches in a way that exposes you to injury in the first place.
• Have the courage to swim against the training tide.
• Life is too short to waste any of it on useless training methods.
• The first requirements for realizing a very demanding goal are lots of resolve, heaps of persistence, and tons of effort. [...] There’s no easy way to reach a demanding goal.
• Gravity in general, and the stress of heavy exercise in particular, compress the joints of the spine, and the muscles and soft tissue of the back as a whole, but especially of the lower back. This is at the root of many back problems. But with the appropriate therapy this compression can be relieved, leading to a healthier and more injury-resistant lower back.
• One of the simplest measures for taking care of the lower back is to take pressure off the lumbar spine. Not only is this inversion therapy a preventative measure, it can help during rehabilitation following injury.
• More isn’t better with inversion therapy (as with much of physical training and therapy). Just one minute or so is all you need to achieve maximum decompression of your spine. A longer duration isn’t necessary, and a shorter time may work very well for you.
• Better to have several very short inversions per day rather than one long one. Invert for up to 60 seconds one or more times per day, and you may experience immediate benefits.
• Even if your body can tolerate singles and very low-rep work, avoid using such high-force training for long periods.
• If your body isn’t suited to singles and very low reps, stick to medium and high reps. Use a rep count for a given exercise that suits your body.
• Avoid medium- and high-impact aerobic and cardio work.
• The harder and more seriously you train, the greater the need to satisfy nutritional requirements. Better to oversupply on the nutritional front than undersupply. Don’t give your all in the gym and then sabotage your progress by cutting corners with your diet!

Make: FPGAs by David Romano

• For the FPGA hobbyist and DIYers, Papilio by Gadget Factory is second to none.
• Papilio series of FPGA development boards and add-on hardware application modules called “Wings” that plug into the main board--sort of like Arduino shields.
• Logic cell ratings are intended to show the logic density of one Xilinx device as compared to another device.
• Like a logic block, the typical cell includes a couple of flip-flops, multiplier, logic gates, and a small amount of RAM for a configurable lookup table (LUT).
• A block RAM (BRAM) is a dedicated two-port memory block containing several kilobits of RAM.
• A DOA (dead on arrival) test is a very popular test for SoC validation engineers to write (typically it is the first test they write for a new chip or design block). This test usually checks to see if the chip or design has any life at all after power-up.
• Logic synthesis is the process by which the register-transfer level (RTL) of the SoC is turned into a design implementation in terms of logic gates, typically by a CAD tool called a synthesis tool.
• We can use a simple binary counter as a clock frequency divider circuit.
• It’s very important to use a naming convention for labeling--this is a good design habit to get yourself into. For small designs, it is not critical, but in larger desigins or joint designs it becomes essential.
• Verilog modules are like functions in other programming languages. They are pieces of code that can be used and reused within a single program.
• Modules can contain both structural and behavioral statements. Structural statements represent circuit components like logic gates, counters, and microprocessors. Behavioral-level statements are programming statements that have no direct mapping to circuit components like loops, if-then statements, and stimulus vectors that are used to exercise a circuit.
• We now can see that a synchronous circuit consists of two kinds of elements: registers and combination logic. Registers (usually implemented as D flip-flops) synchronize the circuit’s operation to the edges of the clock signal, and are the only elements in the circuit that have memory properties. Combinational logic performs all the logical functions in the circuit, and it typically consists of logic gates.
• Binary counters make good frequency dividers.
• Using a simple LED blink test and an FPGA frequency divider is a good vehicle to test the functionality of a new FPGA platform.
• The RTL consists of two kinds of elements: registers and combinational logic. Registers (usually implemented as D flip-flops) synchronize the circuit’s operation to the edges of the clock signal, and are the only elements in the circuit that have memory properties. Combinational logic performs all the logical functions in the circuit, and it typically consists of logic gates.
• Timing issues are the most challenging issues to debug in an FPGA design. For us, it’s good to know that we will not be working with clock speeds that push the envelope of our FPGA technology.
• Doing a simple DOA simulation first, even for small designs, provides a good sanity check to see if the design works functionally at some level.
• Assigning physical I/O connections can be the most difficult part of the whole design process, because this is where you link the virtual world of your ISE design to the real world of the actual FPGA chip and your particular FPGA module circuit board layout.
• The first thing you need to wrap your head around is that when you are coding in HDL, you are not writing a software program; rather, you are describing digital hardware logic functionality.
• With concurrency, there are no sequential steps of code execution like: “first do this, then do this, then do that.” There really is only one instant in time, and that is the clock tick.
• Think of the HDL you are using as more like describing a block diagram than a flow chart.
• Real hardware operates concurrently.
• Concurrency is what differentiates HDL from other programming languages, which are sequential. Concurrency is not explicit in programming languages like C.
• In the simplest sense, a test bench is a virtual testing environment used to verify that a design does everything it’s supposed to do and doesn’t do anything it’s not supposed to do.
• A test bench applies stimuli (inputs) to the unit under test (UUT), also referred to as the device under test (DUT). It monitors the outputs, providing status and error reporting in a readable and user-friendly format.
• The I2C serial bus is a multimaster, multipoint protocol, unlike the very popular UART serial bus protocol, which is point-to-point only.
• Wishbone is an open source hardware computer bus that uses a single simple, high-speed synchronous specification to connect components together in an SoC.
• Waveforms are very useful for viewing large amounts of data quickly and efficiently.
• Graphical analysis is an easy way to see if there is a difference in test results.
• A test bench is a virtual testing environment used to verify that a design does everything it is supposed to do and doesn’t do anything it’s not supposed to do.
• A test bench applies stimuli (inputs) to the unit under test (UUT), also referred to as the device under test (DUT). It monitors the outputs, providing status and error reporting in a readable and user-friendly format.
• The I2C bus is a low-speed, low-power, two-wire serial bus/protocol that is an industry standard for many peripheral devices used in the electronics and computer industry.
• Brian Stuart of Drexel University has written a great piece on CARDIAC, where he explains how the simple instruction set makes for very easy understanding of how complex programs can be out of simpler sets of operations and data.
• VTACH is an OpenCores FPGA project that is actually a Verilog implementation of the original CARDIAC teaching computer from Bell Labs.
• Simple put, an SoC is a semiconductor microchip that contains multiple electronic components integrated together on a single silicon die. This single chip may contain digital, analog, mixed-signal, and even RF (radio frequency) functions that collectively comprise a complete system.
• Gadget Factory’s DesignLab is a great frontend tool for Xilinx ISE schematic entry.
• The ZPUino soft processor core is a 32-bit processor that is easily programmed like the Arduino and is a great building block for FPGA SoCs.
• SDR is a radio communication system where components that have typically been implemented in hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors, etc) are implemented through software, typically in an embedded system or PC.

Compiler Construction by Niklaus Wirth

• Compilers convert program texts into internal code. Hence the constitute the bridge between software and hardware.
• Genuine understanding of a subject is best acquired from an in-depth involvement with both concepts and details.
• We consider syntax analysis as a means to an end, but not as the ultimate goal.
• Computer programs are formulated in a programming language and specify classes of computing processes.
• The construction of the first compiler for the language Fortran around 1956 was a daring enterprise, whose success was not at all assured.
• The translation process essentially consists of the following parts:
• The sequence of characters of a source text is translated into a corresponding sequence of symbols of the vocabulary of the language.
• The sequence of symbols is transformed into a representation that directly mirrors the syntactic structure of the source text and lets this structure easily be recognized.
• High-level languages are characterized by the fact that objects of programs are classified according to their type. Therefore, in addition to syntactic rules, compatibility rules among types of operators and operands define the language. Hence, verification of whether these compatibility rules are observed by a program is an additional duty of a compiler. This verification is called type checking.
• On the basis of the representation resulting from step 2, a sequence of instructions taken from the instruction set of the target computer is generated. This phase is called code generation.
• A partitioning of the compilation process into as many parts as possible was the predominant technique until about 1980, because until then the available [memory] store was too small to accommodate the entire compiler.
• Modern computers with their apparently unlimited stores make it feasible to avoid intermediate storage on disk. And with it, the complicated process of serializing a data structure for output, and its reconstruction on input can be discarded as well.
• A wise compromise exists in the form of a compiler with two parts, namely a front-end and a back-end. The first part comprises lexical and syntax analyses and type checking, and it generates a tree representing the syntactic structure of the source text. This tree is held in main store and constitutes the interface to the second part which handles code generation.
• The idea of decoupling source language and target architecture has also led to projects creating several front ends for different languages generating trees for a single back-end.
• A compiler which generates code for a computer different from the one executing the compiler is called a cross compiler.
• Every language displays a structure called its grammar or syntax.
• A language is defined by the following:
• The set of terminal symbols. These are the symbols that occur in its sentences.
• The set of non-terminal symbols. They denote classes and can be substituted.
• The set of syntactic equations. These define the possible substitutions of non-terminal symbols.
• The start symbol.
• A language is the set of sequences of terminal symbols which, starting with the start symbol, can be generated by repeated application of syntactic equations, that is, substitutions.
• The idea of defining languages and their grammar with mathematical precision goes back to Noam Chomsky.
• The use of the Chomsky formalism is also responsible for the term programming language, because programming languages seemed to exhibit a structure similar to spoken languages.
• A language us "regular", if its syntax can be expressed by a single EBNF expression.
• The method of recursive descent is only one of several techniques to realize the top-down parsing principle.
• Parsing in the bottom-up direction is also called shift-reduce parsing.
• Bottom-up parsing is in general more intricate and complex than top-down parsing.
• Ultimately, the basic idea behind every language is that it should serve as a means for communication. This means that partners must use and understand the same language.
• The scanner has to recognize terminal symbols in the source text.
• As soon as an unacceptable symbol turns up, the task of the parser is completed, and the process of syntax analysis is terminate.
• We postulate the following quality criteria for error handling:
• As many errors as possible must be detected in a single scan through the text.
• As few additional assumptions as possible about the language are to be made.
• Error handling features should not slow down the parser appreciably.
• The parser program should not grow in size significantly.
• Without doubt, a simple language structure significantly simplifies error diagnostics, or, in other words, a complicated syntax complicates error handling unnecessarily.
• The essential characteristics of a good compiler, regardless of details, are that (1) no sequence of symbols leads to its crash, and (2) frequently encountered errors are correctly diagnosed and subsequently generate no, or few additional, spurious error messages.
• Context is represented by a data structure which contains an entry for every declared identifier. This entry associates the identifier with the denoted object and its properties. The data structure is known by the name symbol table.
• Every declaration results in a new symbol table entry.
• Every occurrence of an identifier in a statement requires a search of the symbol table in order to determine the attributes (properties) of the object denoted by the identifier.
• The simplest form of data structure for representing a set of items is the list. Its major disadvantage is a relatively slow search process, because it has to be traversed from its root to the desired element.
• In order to speed up the search process, the list is often replaced by a tree structure. Its advantage becomes noticeable only with a fairly large number of entries.
• In languages featuring data types, their consistency checking is one of the most important tasks of a compiler. The checks are based on the type attribute recorded in every symbol table entry.
• We must determine the format in which data are to be represented at run-time in the [memory] store. The choice inherently depends on the target architecture, although this fact is less apparent because of the similarity of virtually all computers in this respect.
• Every computer features certain elementary data types together with corresponding instructions, such as integer addition and floating-point addition. These types are invariably scalar types, and they occupy a small number of consecutive memory locations (bytes).
• The size of an array is its element size multiplied by the number of its elements. The address of an element is the sum of the array's address and the elment's index multiplied by the element size.
• Absolute addresses of variables are usually unknown at the time of compilation. All generated addresses must be considered as relative to a common base address which is given at run-time. The effective address is then the sum of this base address and the address determined by the compiler.
• Although bytes can be accessed individually, typically a small number of bytes are transferred from or to memory as a packet, a so-called word.
• If allocation occurs strictly in sequential order it is possible that a variable may occupy (parts of) several words. But this should be avoided, because otherwise a variable access would involve several memory accesses, resulting in an appreciable slowdown.
• A simple method of overcoming this problem is to round up (or down) each variable's address to the next multiple of its size. This process is called alignment.
• The price of alignment is the loss of some bytes in memory, which is quite negligible.
• Following a longstanding tradition, addresses of variables are assigned negative values, that is, negative offsets to the common base address determined during program execution.
• The acronym RISC stands for reduced instruction set computer, where "reduced" is to be understood as relative to architectures with large sets of complex instructions.
• From the viewpoints of the programmer and the compiler designer the computer consists of an arithmetic unit, a control unit and a store.
• Register instructions operate on registers only and feed data through a shifter and the arithmetic logic unit ALU.
• Memory instructions fetch and store data in memory.
• Branch instructions affect the program counter.
• Our ideal computer would be capable of directly interpreting post-fix notation. Such an ideal computer requires a stack for holding intermediate results. Such a computer architecture is called a stack architecture.
• Whenever arithmetic expression are evaluated, the inherent danger of overflow exists. The evaluating systems should therefore be suitably guarded.
• The essence of delayed code generation is that code is not emitted before it is clear that no better solution exists.
• Conditional and repeated statements are implemented with the aid of jump instructions, also called branch instructions.
• Procedures, which are also known as subroutines, are perhaps the most important tool for structuring programs. Because of their frequency of occurrence, it is mandatory that their implementation is efficient. Implementation is based on the branch instructions which saves the current PC value and thereby the point of return after termination of the procedure, when this value is reloaded into the PC register.
• Algol-60 introduced the very fundamental concept of local variables. It implied that every identifier declared had a limited range of visibility and validity.
• In concrete terms, variables may be declared local to a procedure such that they are visible and valid within this procedure only.
• Addresses of local variables generated by the compiler are always relative to the base address of the respective activation frame. Since in programs most variables are local, their addressing also must be highly efficient. This is achieved by reserving a register to hold the base address, and to make use of the fact that the effective address is the sum of a register value and the instruction's address field.
• Parameters constitute the interface between the calling and the called procedures. Parameters on the calling side are said to be actual parameters, and those on the called side formal parameters. The latter are in fact only place holders for which the actual parameters are substituted.
• Most programming languages distinguish between at least two kinds of parameters. The first is the value parameter where, as its name  suggests, the value of the actual parameter is assigned to the formal variable. The second kind of parameter is the reference parameters, where, also as suggested by its name, a reference to the actual parameter is assigned to the formal variable.
• The fact that with real numbers only approximate results can be obtained, may be understood by considering that real numbers are represented by scaled integers with a fixed, finite number of digits.
• In many computers, instructions for floating-point operands use a special set of registers. The reason behind this is that often separate co-processors, so-called floating-point units (FPUs) are used which implement all floating-point instructions and contain this set of floating-point registers.
• In order to be complete, a computer's set of instructions must also contain conversion instructions which convert integers into floating-point numbers and vice-versa. The same holds at the level of the programming language.
• Conversions between integer types are simple and efficient, because they consist of a sign extension only.
• An open array is an array parameter whose length is unknown (open) at the time of compilation.
• The two forms of data structures provided in Oberon are the array (all elements of the same type, homogeneous structure) and the record (heterogeneous structure).
• If every pointer variable is initialized to NIL, it suffices to precede every access via a pointer with a test for the pointer value NIL.
• A variable is no longer relevant when there are no references to it.
• The principle advantage of separate compilation is that changes in a module M do not invalidate clients of M, if the interface of M remains unaffected.
• A primary goal of good code optimization is the most effective use of registers in order to reduce the number of accesses to the relatively slow main memory. A good strategy of register usage yields more advantages than any other branch of optimization.

xv6: a simple, Unix-like teaching operating system

• The job of an operating system is to share a computer among multiple programs and to provide a more useful set of services than the hardware alone supports.
• An operating system provides services to user programs through an interface.
• Each running program, called a process, has memory containing instructions, data, and a stack. The instructions implement the program's computation. The data are the variables on which the computation acts. The stack organizes the program's procedure calls.
• When a process needs to invoke a kernel service, it invokes a procedure call in the operating system interface. Such a procedure call is called a system call. The system call enters the kernel; the kernel performs the service and returns.
• The kernel uses the CPU's hardware protection mechanisms to ensure that each process executing in user space can access only its own memory.
• The shell is an ordinary program that reads commands from the user and executes them, and is the primary user interface to traditional Unix-like systems.
• An xv6 process consists of user-space memory (instructions, data, and stack) and per-process state private to the kernel.
• The exec system call replaces the calling process's memory with a new memory image loaded from a file stored in the file system.
• A process that needs more memory at run-time (perhaps for malloc) can call sbrk(n) to grow its data memory by n bytes; sbrk returns the location of the new memory.
• A file descriptor is a small integer representing a kernel-managed object that a process may read from or write to.
• Internally, the xv6 kernel uses the file descriptor as an index into a per-process table, so that every process has a private space of file descriptors starting at zero.
• By convention, a process read from file descriptor 0 (standard input), writes to file descriptor 1 (standard output), and writes error messages to file descriptor 2 (standard error).
• The read and write system calls read bytes from and write bytes to open files named by file descriptors.
• Each file descriptor that refers to a file has an offset associated with it. Read reads data from the current file offset and then advances that offset by the number of bytes read: a subsequent read will return the bytes following the ones returned by the first read.
• Like read, write writes data at the current file offset and then advances that offset by the number of bytes written: each write picks up where the previous one left off.
• A newly allocated file descriptor is always the lowest-numbered unused descriptor of the current process.
• Fork copies the parent's file descriptor table along with its memory, so that the child starts with exactly the same open files as the parent.
• The dup system call duplicates an existing file descriptor, returning a new one that refers to the same underlying I/O object.
• File descriptors are a powerful abstraction, because they hide the details of what they are connected to: a process writing to file descriptor 1 may be writing to a file, to a device like the console, or to a pipe.
• A pipe is a small kernel buffer exposed to processes as a pair of file descriptors, one for reading and one for writing. Writing data to one end of the pipe makes that data available for reading from the other end of the pipe.
• Pipes provide a way for processes to communicate.
• Pipes allow for synchronization: two processes can use a pair of pipes to send messages back and forth to each other, with each read blocking its calling process until the other process has sent data with write.
• A file's name is distinct from the file itself; the same underlying file, called an inode, can have multiple names, called links.
• The link system call creates another file system name referring to the same inode as an existing file.
• Each inode is identified by a unique inode number.
• Unix's combination of the "standard" file descriptors, pipes, and convenient shell syntax for operations on them was a major advance in writing general-purpose reusable programs.
• The authors of Unix went on to build Plan 9, which applied the "resources are files" concept to modern facilities, representing networks, graphics, and other resources as files or file trees.
• Any operating system must multiplex processes onto the underlying hardware, isolate processes from each other, and provide mechanisms for controlled inter-process communication.
• The implementation of an operating system must achieve three requirements: multiplexing, isolation, and interaction.
• To achieve strong isolation a helpful approach is to disallow applications to have direct access to the hardware resources, but instead to abstract the resources into services.
• In kernel mode, the processor is allowed to execute privileged instructions.
• The software running in kernel space (or in kernel mode) is called the kernel.
• A key design question for an operating system is what part of the operating system should run in kernel mode.
• The unit of isolation in xv6 is a process.
• A process is an abstraction that provides the illusion to a program that it has its own abstract machine.
• The x86 page table translates (or "maps) a virtual address (the address that an x86 instruction manipulates) to a physical address (an address that the processor chip sends to main memory).
• The xv6 kernel maintains many pieces of state for each process, which it gathers into a struct proc. A process's most important pieces of kernel state are its page table, its kernel stack, and its run state.
• Each process has two stacks: a user stack and a kernel stack.
• When a process makes a system call, the processor switches  to the kernel stack, raises the hardware privilege level, and starts executing the kernel instructions that implement the system call. When the system call completes, the kernel returns to user space: the hardware lowers its privilege level, switches back to the user stack, and resumes executing user instructions just after the system call instruction.
• Page tables are the mechanism through which the operating system controls what memory addresses mean.
• An x86 page table is logically an array of 2^20 page table entries (PTEs). Each PTE contains a 20-bit physical page number (PPN) and some flags. The paging hardware translates a virtual address by using its top 20 bits with the PPN in the PTE. The paging hardware copies the low 12 bits unchanged from the virtual to the translated physical address.
• A page table is stored in physical memory as a two-level tree. [...] This two-level structure allows a page table to omit entire page table pages in the common case in which large ranges of virtual addresses have no mappings.
• Physical memory refers to storage cells in DRAM. A byte of physical memory has an address, called a physical address. Instructions use only virtual addresses, which the paging hardware translates to physical addresses, and then sends to the DRAM hardware to read or write storage.
• Each process has a separate page table, and xv6 tells the page table hardware to switch page tables when xv6 switches between processes.
• Different processes' page tables translate user addresses to different pages of physical memory, so that each process has private user memory.
• To guard a stack growing off the stack page, xv6 places a guard page right below the stack. The guard page is not mapped and so if the stack runs off the stack page, the hardware will generate an exception because it cannot translate the faulting address.
• Exec is the system call that creates the user part of an address space. It initializes the user part of an address space from a file stored in the file system.
• If the ELF header has the right magic number, exec assumes that the binary is well-formed.
• Small pages make sens when physical memory is small, to allow allocation and page-out to disk with fine granularity.
• Larger pages make sense on machines with lots of RAM, and may reduce overhead for page-table manipulation.
• Today people care more about speed than space-efficiency.
• When running a process, a CPU executes the normal processor loop: read an instruction, advance the program counter, execute the instruction, repeat.
• The term exception refers to an illegal program action that generates an interrupt.
• The term interrupt refers to a signal generated by a hardware device, indicating that it needs attention of the operating system.
• The kernel handles all interrupts, rather than processes handling them, because in most cases only the kernel has the required privilege and state.
• An interrupt stops the normal processor loop and starts executing a new sequence called an interrupt handler.
• It is important to remember that traps are caused by the current process running on a processor, and interrupts are caused by devices and may not be related to the currently running process.
• The x86 has 4 protection levels, numbered 0 (most privileged) to 3 (least privilege). In practice, most operating systems use only 2 levels: 0 and 3, which are then called kernel mode and user mode, respectively.
• The current privilege level with which the x86 executes instructions is stored in the %cs register, in the field CPL.
• On the x86, interrupt handlers are defined in the interrupt descriptor table (IDT). The IDT has 256 entries, each giving the %cs and %eip to be used when handling the corresponding interrupt.
• To make a system cal on the x86, a program invokes the int n instruction, where n specifies the index into the IDT.
• An operating system can use the iret instruction to return from an int instruction. It pops the saved values during the int instruction from the stack, and resumes execution at the saved %eip.
• System calls conventionally return negative numbers to indicate errors, positive numbers for success.
• Interrupts are similar to system calls, except devices generate them at any time.
• A processor can control if it wants to receive interrupts through the IF flag in the eflags register. The instruction cli disables interrupts on the process by clearing IF, and sti enables interrupts on a processor.
• xv6 disables interrupts during booting of the main cpu and the other processors.
• A driver is the piece of code in an operating system that manages a particular device: it provides interrupt handlers for a device, causes a device to perform operations, cases a device to generate interrupts, etc.
• Driver code can be tricky to write because a driver executes concurrently with the device that it manages.
• In many operating systems, the drivers together account for more code in the operating system than the core kernel.
• Typically devices are slower than CPU, so the hardware uses interrupts to notify the operating system of status changes.
• Using DMA means that the CPU is not involved at all in the [data] transfer, which can be more efficient and is less taxing for the CPU's memory caches.
• All modern devices are programmed using memory-mapped I/O.
• A lock provides mutual exclusion, ensuring that only one CPU at a time can hold the lock.
• In one atomic operation, xchg swaps a word in memory with the contents of a register.
• Interrupts can cause concurrency even on a single processor: if interrupts are enabled, kernel code can be stopped at any moment to run an interrupt handler instead.
• It is possible to implement locks without atomic instructions, but it is expensive, and most operating systems use atomic instructions.
• Any operating system is likely to run with more processes than the computer has processors, and so a plan is needed to time-share the processors among the processes.
• Switching from one thread to another involves saving the old thread's CPU registers, and restoring previously-saved registers of the new thread; the fact that %esp and %eip are saved and restored means that the CPU will switch stacks and switch what code it is executing.
• Each pipe is represented by a struct pipe, which contains a lock and a data buffer.
• The xv6 scheduler implements a simple scheduling policy, which runs each process in turn. This policy is called round robin.
• A semaphore is an integer value with two operations, increment and decrement (or up and down). It is always possible to increment a semaphore, but the semaphore value is not allowed to drop below zero.
• The purpose of a file system is to organize and store data.
• One of the most interesting problems in file system design is crash recovery. The problem arises because many file system operations involve multiple writes to the disk, and a  crash after a subset of the writes may leave the on-disk file system in an inconsistent state.
• One of the cool aspects of the Unix interface is that most  resources in Unix are represented as a file, including devices such as the console, pipes, and of course, real files. The file descriptor layer is the layer that achieves this uniformity.
• All the open files in the system are kept in a global file table, the ftable.
• From our point of view, we can abstract the PC into three components: CPU, memory, and input/output (I/O) devices. The CPU performs computation, the memory contains instructions and data for that computation, and devices allow the CPU to interact with hardware for storage, communication, and other functions.
• A computer's CPU runs a conceptually simple loop: it consults an address in a register called the program counter, reads a machine instruction from that address in memory, advances the program counter past the instruction, and executes the instruction. Repeat.
• A register is a storage cell inside the processor itself, capable of holding a machine word-sized value.
• The modern x86 provides eight general purpose 32-bit registers: eax, ebx, ecx, edx, edi, esi, ebp, and esp--and a program counter eip.
• Registers are fast but expensive.
• Main memory is 10-100x slower than a register, but it is much cheaper, so there can be more of it. One reason main memory is relatively slow is that it is physically separate from the processor chip.
• The x86 processor provides special in and out instructions that read and write values from device address called I/O ports.