Skip to content

Latest commit

 

History

History
104 lines (81 loc) · 5.23 KB

README.md

File metadata and controls

104 lines (81 loc) · 5.23 KB
Raw

Scott CPU assembler

A machine code assembler for the CPU designed in the book But How Do It Know? by J. Clark Scott.

Build

The assembler consists of a single .c file that can be built using:

make

from the projects root directory.

The assembler was built and has been tested using clang on Mac OS X but should compile using gcc on Linux just fine.

Run

To invoke the assembler, use:

./sca <file>

where <file> is the name of the assembly file you want to compile. For example to compile the multiply.asm example, issue:

./sca examples/multiply.asm

This will output a file with .bin replacing .asm extension in the same directory i.e. examples/multiply.bin. This is the binary output file. Note: this file extension replace will replace the extension after the first . found in the file or append .bin if no file extension is found e.g:

my_assembly_file.txt -> my_assembly_file.bin

my_assembly_file2 -> my_assembly_file2.bin

Instruction Set

Arithmetic and Logic Instructions

Opcode (binary) Opcode (hex) Mnemonic Operands Description Operation Flags #Clocks
1000____ 8_ ADD RA, RB Add the contents of RA to RB and store result in RB RB ← RA + RB C, A, E, Z 3
1001____ 9_ SHR RA, RB Right shift the contents of RA and store result in RB RB ← RA >> 1 C, A, E, Z 3
1010____ A_ SHL RA, RB Left shift the contents of RA and store result in RB RB ← RA << 1 C, A, E, Z 3
1011____ B_ NOT RA, RB NOT RA and store the result in RB RB ← ~RA A, E, Z 3
1100____ C_ AND RA, RB AND RA and RB and store the result in RB RB ← RA & RB A, E, Z 3
1101____ D_ OR RA, RB OR RA and RB and store the result in RB RB ← RA | RB A, E, Z 3
1110____ E_ XOR RA, RB XOR RA and RB and store the result in RB RB ← RA ^ RB A, E, Z 3
1111____ F_ CMP RA, RB Compare RA and RB RA - RB A, E, Z 3

Load and Store Instructions

Opcode (binary) Opcode (hex) Mnemonic Operands Description Operation Flags #Clocks
0000____ 0_ LD RA, RB Load RB from RAM at RAM address in RA RB ← [RA] - (2) 3
0001____ 1_ ST RA, RB Store RB into RAM at RAM address in RA [RA] ← RB - (2) 3

Data Instruction

Opcode (binary) Opcode (hex) Mnemonic Operands Description Operation Flags #Clocks
001000__ 2_ DATA RB, K Load byte constant, K into RB RB ← K - 3

Branch Instructions

Opcode (binary) Opcode (hex) Mnemonic Operands Description Operation Flags #Clocks
001100__ 3_ JMPR RB Jump to the RAM address stored in RB IAR ← RB - (1) 3
01000000 40 JMP K Jump to the RAM address K IAR ← K - (2) 3
01011000 58 JC K Jump to RAM address K if the 'carry' flag is set If (C == 1) then IAR ← K - 3
01010100 54 JA K Jump to RAM address K if the 'a is larger' flag is set If (A == 1) then IAR ← K - 3
01010010 52 JE K Jump to RAM address K if the 'equal' flag is set If (E == 1) then IAR ← K - 3
01010001 51 JZ K Jump to RAM address K if the 'zero' flag is set If (Z == 1) then IAR ← K - 3
01011100 5C JCA K Jump to RAM address K if C or A are set If (C == 1 or A ==1) then IAR ← K - 3
01011010 5A JCE K Jump to RAM address K if C or E are set If (C == 1 or E ==1) then IAR ← K - 3
01011001 59 JCZ K Jump to RAM address K if C or Z are set If (C == 1 or Z ==1) then IAR ← K - 3
01010110 56 JAE K Jump to RAM address K if A or E are set If (A == 1 or E ==1) then IAR ← K - 3
01010101 55 JAZ K Jump to RAM address K if A or Z are set If (A == 1 or Z ==1) then IAR ← K - 3
01010011 53 JEZ K Jump to RAM address K if E or Z are set If (E == 1 or Z ==1) then IAR ← K - 3
01011110 5E JCAE K Jump to RAM address K if C or A or E are set If (C == 1 or A ==1 or E == 1) then IAR ← K - 3
01011101 5D JCAZ K Jump to RAM address K if C or A or Z are set If (C == 1 or A ==1 or Z == 1) then IAR ← K - 3
01011011 5B JCEZ K Jump to RAM address K if C or E or Z are set If (C == 1 or Z ==1 or Z == 1) then IAR ← K - 3
01010111 57 JAEZ K Jump to RAM address K if A or E or Z are set If (A == 1 or E ==1 or Z == 1) then IAR ← K - 3
01011111 5F JCAEZ K Jump to RAM address K if C or A or E or Z are set If (C == 1 or A ==1 or E == 1 or Z == 1) then IAR ← K - 3

Clear Flags Instruction

Opcode (binary) Opcode (hex) Mnemonic Operands Description Operation Flags #Clocks
01100000 60 CLF - Clear all flags C = A = E = Z = 0 C, A, E, Z (1) 3

IO Instructions

Opcode (binary) Opcode (hex) Mnemonic Operands Description Operation Flags #Clocks
011100__ 7_ IND RB Input IO data to RB IO (data) ← RB - (1) 3
011101__ 7_ INA RB Input IO address to RB IO (address) ← RB - (1) 3
011110__ 7_ OUTD RB Output RB to IO as data RB ← IO (data) - (1) 3
011111__ 7_ OUTA RB Output RB to IO as address RB ← IO (address) - (1) 3

TODO

  • -o output file cmd line option
  • label implementation for branching rather than specifying absolute addresses
  • org directive to add constants to label addresses