LC-3 Assembly Language definition for customasm

LC-3.asm

#once

; LC3 Instruction Set Assembly for customasm (https://github.com/hlorenzi/customasm)
;
; References: 
;   Patt, Yale N.; Patel, Sanjay (2003). Introduction to Computing Systems: 
;   From Bits and Gates to C and Beyond. New York, NY: McGraw-Hill Higher 
;   Education. ISBN 0-07-246750-9.

#bankdef lc3_bank
{
	#bits 16 ; (Addresable) Word-size
    #addr 0x3000 ; Starting logical address
    #addr_end 0x10000 ; Ending logical address (exclusive)
	#outp 0
}

#subruledef lc3_reg
{
    R{n: u3} => n`3
}

; (Only for 9-bit offsets)
#subruledef lc3_label
{
    {addr} =>
    {
        offset = addr - ($ + 1)
	assert(offset <= 255)
	assert(offset >= -256)
        offset
    }
}

#ruledef lc3
{
; Addition
    ADD {dr: lc3_reg}, {sr1: lc3_reg}, {sr2: lc3_reg} => 0b0001 @ dr @ sr1 @ 0b000 @ sr2
    ADD {dr: lc3_reg}, {sr1: lc3_reg}, {imm: s5} => 0b0001 @ dr @ sr1 @ 0b1 @ imm

; Bit-wise Logical And
    AND {dr: lc3_reg}, {sr1: lc3_reg}, {sr2: lc3_reg} => 0b0101 @ dr @ sr1 @ 0b000 @ sr2
    AND {dr: lc3_reg}, {sr1: lc3_reg}, {imm: s5} => 0b0101 @ dr @ sr1 @ 0b1 @ imm

; Conditional Branch instructions
    BR {offset: lc3_label}    => 0b0000 @ 0b000 @ offset`9
	BRn {offset: lc3_label}   => 0b0000 @ 0b100 @ offset`9
    BRz {offset: lc3_label}   => 0b0000 @ 0b010 @ offset`9 
    BRp {offset: lc3_label}   => 0b0000 @ 0b001 @ offset`9
    BRzp {offset: lc3_label}  => 0b0000 @ 0b011 @ offset`9
    BRnp {offset: lc3_label}  => 0b0000 @ 0b101 @ offset`9 
    BRnz {offset: lc3_label}  => 0b0000 @ 0b110 @ offset`9 
    BRnzp {offset: lc3_label} => 0b0000 @ 0b111 @ offset`9
	
; Jump / Return from Subroutine
    JMP {BaseR: lc3_reg} => 0b1100 @ 0b000 @ BaseR @ 0`6
    RET                  => asm { JMP R7 }
    
; Jump to Subroutine
    JSR {label} => 
	{
		offset = label - ($ + 1)
		assert(offset <= 1023)
		assert(offset >= -1024)
		0b0100 @ 0b1 @ offset`11
	}

    JSRR {BaseR: lc3_reg} => 0b0100 @ 0b0 @ 0b00 @ BaseR @ 0`6
	
; Load instrutions
    LD {dr: lc3_reg}, {offset: lc3_label} => 0b0010 @ dr @ offset`9
    LDI {dr: lc3_reg}, {offset: lc3_label} => 0b1010 @ dr @ offset`9
    LDR {dr: lc3_reg} , {BaseR: lc3_reg}, {offset: s6} => 0b0110 @ dr @ BaseR @ offset 

; Load Effective Address
	LEA {dr: lc3_reg}, {offset: lc3_label} => 0b1110 @ dr @ offset`9

; Bit-Wise Complement
	NOT {dr: lc3_reg}, {sr: lc3_reg} => 0b1001 @ dr @ sr @ 0b111111
	
; Return from Trap or Interrupt
    RTI => 0b1000 @ 0`12
	
; Store instructions
    ST {sr: lc3_reg}, {offset: lc3_label} => 0b0011 @ sr @ offset`9
    STI {sr: lc3_reg}, {offset: lc3_label} => 0b1011 @ sr @ offset`9
    STR {sr: lc3_reg}, {BaseR: lc3_reg}, {offset: s6} => 0b0111 @ sr @ BaseR @ offset

; System Call
	TRAP {trapvect: u8} => 0b1111 @ 0b0000 @ trapvect`8

; Trap Service Routines (specific aliases for TRAP)
	GETC  => asm { TRAP 0x20 }
	OUT   => asm { TRAP 0x21 }
	PUTS  => asm { TRAP 0x22 }
	IN    => asm { TRAP 0x23 }
	PUTSP => asm { TRAP 0x24 }
	HALT  => asm { TRAP 0x25 }
}

; STRINGZ - Null-terminated string as 16-bit big-endian words
;
; --- Example usage ---
;
; alias:
;   #d STRINGZ("my_string")
;
#fn STRINGZ(param) => utf16be(param) @ 0x0000

; FILL - Fill next word with value (truncating!)
;
; --- Example usage ---
;
; six:
;   #d FILL(6)
;	#d16 0x0006		; Alternative
;
#fn FILL(value) => value`16