1. Assembler Program

The Elements of Computing Systems evolves around the construction of a complete computer system, done in the framework of a 1- or 2-semester course. In the first part of the book/course, we build the hardware platform of a simple yet powerful computer, called Hack.

In the second part, we build the computer’s software hierarchy, consisting of an assembler, a virtual machine, a simple Java-like language called Jack, a compiler for it, and a mini operating system, written in Jack. The book/course is completely self-contained, requiring only programming as a pre-requisite.

The book’s web site includes some 200 test programs, test scripts, and all the software tools necessary for doing all the projects. The machine code generated by the assembler can be tested either in the hardware simulator or in the CPU emulator. (All the supplied tools are dual-platform:Xxx.bat startsXxx in Windows, and Xxx.sh starts it in Unix) Simulators(HardwareSimulator, CPUEmulator, VMEmulator):. Used to build hardware platforms andexecute programs;. Supplied by us. Translators (Assembler, JackCompiler):. Used to translate from high-level to low-level;.

System software: all software designed either to control the computer system or to assist users in running applications or prog4rammers in developing software. It includes operating Chapter 2 Assemblers.

Developed by the students, using the book’s specs; Executable solutions supplied by us. Other. Bin: simulators and translators software;. builtIn: executable versions of all the logic gates and chips mentioned in the book;. OS: executable version of the Jack OS;. TextComparer: a text comparison utility. 00000000000110000000000000000000011 Assembler Sum.asm // Computes sum=1+.+100.

@i // i=1 M=1 @sum // sum=0 M=0 (LOOP) @i // if (i-100)=0 goto END D=M @100 D=D-A @END D;JGT @i // sum+=i D=M @sum M=D+M @i // i M=M+1 @LOOP // goto LOOP 0;JMP (END) // infinite loop @END 0;JMP. Sum.asm // Computes sum=1+.+100. @i // i=1 M=1 @sum // sum=0 M=0 (LOOP) @i // if (i-100)=0 goto END D=M @100 D=D-A @END D;JGT @i // sum+=i D=M @sum M=D+M @i // i M=M+1 @LOOP // goto LOOP 0;JMP (END) // infinite loop @END 0;JMP The assembly program:. Stored in a text file named Prog.asm. Written and edited in a text editor The assembly process:.

Translates Prog.asm into Prog.hack. Eliminates comments and white space. Allocates variables (e.g. Iand sum) to memory. Translates each assembly command into a single 16-bit instruction written in the Hack machine language. Treats label declarations like (LOOP)and (END) as pseudo commands that generate no code.

To their meaning On weekends, my father would take me for walks in the woods and he’d tell me about interesting things that were going on. “See that bird?” he says. “It’s a Spencer Warbler.” (I knew he didn’t know the real name.) “Well, in Italian, it’s Chutto Lapittida. In Portuguese, it’s a Bom da Peida.

In Chinese, it’s a Chung-long-tah, and in Japanese, it’s Katano Tekeda. You can know the name of that bird in all the languages of the world, but when you’re finished, you’ll know absolutely nothing whatever about the bird. You’ll only know something about people in different places, and what they call the bird.

So let’s look at the bird and see what it is doing – that’s what counts.” This is how I learned very early the difference between knowing the name of something and knowing something. Feynman, The Making of a Scientist, 1988.

Assembler Program

Title: A Simple Two-Pass Assembler 1 A Simple Two-Pass Assembler 2 Main Functions. Translate mnemonic operation codes to their machine language equivalents. Assign machine addresses to symbolic labels used by the programmers Depend heavily on the source language it translates and the machine language it produces. E.g., the instruction format and addressing modes 3 Basic Functions 4 Example 2.1 Line numbers are not part of the program. They are for reference only.

Forward reference Call subroutine code 5 Comment line Indexing mode Hexadecimal number 6 Subroutine entry point Subroutine return point 7 Purpose of Example 2.1 (COPY). It is a copy function that reads some records from a specified input device and then copies them to a specified output device. Reads a record from the input device (code F1). Copies the record to the output device (code 05). Repeats the above steps until encountering EOF. Then writes EOF to the output device. Then call RSUB to return to the caller 8 RDREC and WRREC.

Data transfer. A record is a stream of bytes with a null character (0016) at the end. If a record is longer than 4096 bytes, only the first 4096 bytes are copied. EOF is indicated by a zero-length record. (I.e., a byte stream with only a null character. Because the speed of the input and output devices may be different, a buffer is used to temporarily store the record.

Subroutine call and return. On line 10, STL RETADDR is called to save the return address that is already stored in register L. Otherwise, after calling RD or WR, this COPY cannot return back to its caller.

9 Assembler Directives. Assembler directives are pseudo instructions. They will not be translated into machine instructions. They only provide instruction/direction/informatio n to the assembler. Basic assembler directives. START.

Specify name and starting address for the program. END. Indicate the end of the source program, and (optionally) the first executable instruction in the program. 10 Assembler Directives (contd). BYTE.

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