First/assembly.c

#include "assembly.h"
#include <string.h>
#include <stdlib.h>
#include <stdio.h>


// Max instruction width is 25 characters without the null char
//
// INSTRUCTIONS:
//    BYTE 3       BYTE 2       BYTE 1       BYTE 0
// +===================================================+
// |            |            |            |            |
// +===================================================+
//
//
//
// INSTRUCTION FORMAT 0:
// +===================================================+
// | OPCODE     |      24 BIT IMMEDIATE ADDRESS        |
// +===================================================+
//
// INSTRUCTION FORMAT 1:
// +===================================================+
// |          OPCODE         | SOURCE REG | DEST REG   |
// +===================================================+
//
// INSTRUCTION FORMAT 2:
// +===================================================+
// |   OPCODE   | DEST REG   |    16 BIT IMMEDIATE     |
// +===================================================+
//
//
//
//  OPCODE FORMAT:
//  ______________________________________________________________________________________________________
//  |BIT | 0   | 1   | 2   | 3   | 4   | 5   | 6   | 7   | 8   | 9   | 10  | 11  | 12  | 13  | 14  | 15  |
//  +----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
//  |    | INSTR. FORMAT   |    8bit opcode num          :          16bit opcode num                     |
//  +----+-----------------+-----------------------------+-----------------------------------------------+
//
//
//  INSTRUCTION FORMAT 0 OPCODE NUM:
//  +-------+----------------------------------+--------------+
//  | NUM   | DESCRIPTION                      | AFFECT FLAGS |
//  +-------+----------------------------------+--------------+
//  | 5'd0  | NOP                              |      NO      |
//  +-------+----------------------------------+--------------+
//  | 5'd1  | Unconditional Jump               |      NO      |
//  +-------+----------------------------------+--------------+
//  | 5'd2  | Jump if zero flag is set         |      NO      |
//  +-------+----------------------------------+--------------+
//  | 5'd3  | Jump if zero flag is not set     |      NO      |
//  +-------+----------------------------------+--------------+
//  | 5'd4  | Jump if carry flag is set        |      NO      |
//  +-------+----------------------------------+--------------+
//  | 5'd5  | Jump if carry flag is not set    |      NO      |
//
//
//  INSTRUCTION FORMAT 1 OPCODE NUM:
//  +-------+----------------------------------+--------------+
//  | NUM   | DESCRIPTION                      | AFFECT FLAGS |
//  +-------+----------------------------------+--------------+
//  | 13'd0 | ADD                              |      YES     |
//  +-------+----------------------------------+--------------|
//  | 13'd1 | SUBTRACT                         |      YES     |
//  +-------+----------------------------------+--------------|
//  | 13'd2 | SHIFT LEFT                       |      YES     |
//  +-------+----------------------------------+--------------|
//  | 13'd3 | SHIFT RIGHT                      |      YES     |
//  +-------+----------------------------------+--------------|
//  | 13'd4 | COMPARE  (SUBTRACT WITHOUT SAVE) |      YES     |
//
//
//  INSTRUCTION FORMAT 2 OPCODE NUM:
//  +-------+----------------------------------------------+--------------+
//  | NUM   | DESCRIPTION                                  | AFFECT FLAGS |
//  +-------+----------------------------------------------+--------------+
//  | 5'd0 | MOV IMMEDIATE TO DEST LOW PART OF REGISTER    |      NO      |
//  +-------+----------------------------------------------+--------------+
//  | 5'd1 | MOV IMMEDIATE TO DEST HIGH PART OF REGISTER   |      NO      |

#define MAX_INSTRUCTION_LENGTH 26

char *disassemble(uint32_t opcode_be){
	uint32_t opcode=(opcode_be&0x000000FF)<<24|(opcode_be&0x0000FF00)<<8|(opcode_be&0x00FF0000)>>8|(opcode_be&0xFF000000)>>24;
	char *ret=malloc(MAX_INSTRUCTION_LENGTH);

	if (!ret)
		return NULL;

	//////// PARSE BITECODE //////////

	int instruction_format,opcode_num;
	uint32_t val;
	uint8_t val1;
	uint8_t val2;

	instruction_format=(opcode&0xE0000000)>>29;
	if(instruction_format==0){
		// 8bit opcode
		opcode_num=(opcode&0x1F000000)>>24;
		val=opcode&0x00FFFFFF;

		switch(opcode_num){
			case 0x00:
				snprintf(ret,MAX_INSTRUCTION_LENGTH,"NOP");
				break;
			case 0x01:
				snprintf(ret,MAX_INSTRUCTION_LENGTH,"JMP $%06X",val);
				break;
			case 0x02:
			case 0x03:
				snprintf(ret,MAX_INSTRUCTION_LENGTH,"JMP %s,$%06X",opcode_num&1?"Z":"NZ",val);
				break;
			case 0x04:
			case 0x05:
				snprintf(ret,MAX_INSTRUCTION_LENGTH,"JMP %s,$%06X",opcode_num&1?"C":"NC",val);
				break;
			default:
				snprintf(ret,MAX_INSTRUCTION_LENGTH,"UNRECOGNISED INSTR");
				break;
		}
	}else if(instruction_format==1){
		// 16bit opcode
		opcode_num=(opcode&0x1FFF0000)>>16;
		val1=(opcode&0x0000FF00)>>8;
		val2=opcode&0x000000FF;

		switch(opcode_num){
			case 0x00:
				snprintf(ret,MAX_INSTRUCTION_LENGTH,"ADD %%R%0d, %%R%0d",val1,val2);
				break;
			case 0x01:
				snprintf(ret,MAX_INSTRUCTION_LENGTH,"SUB %%R%0d, %%R%0d",val1,val2);
				break;
			case 0x02:
				snprintf(ret,MAX_INSTRUCTION_LENGTH,"SL %%R%0d",val1);
				break;
			case 0x03:
				snprintf(ret,MAX_INSTRUCTION_LENGTH,"SR %%R%0d",val1);
				break;
			case 0x04:
				snprintf(ret,MAX_INSTRUCTION_LENGTH,"CMP %%R%0d, %%R%0d",val1,val2);
				break;
			default:
				snprintf(ret,MAX_INSTRUCTION_LENGTH,"UNRECOGNISED INSTRUCTION");
				break;
		}
	}else if(instruction_format==2){
		// 16bit opcode
		opcode_num=(opcode&0x1FFF0000)>>16;
		val1=(opcode&0x00FF0000)>>16;
		val=opcode&0x0000FFFF;

		switch(opcode_num){
			case 0x00:
				snprintf(ret,MAX_INSTRUCTION_LENGTH,"MOV $%04X, %%R%0dl",val,val1);
				break;
			case 0x01:
				snprintf(ret,MAX_INSTRUCTION_LENGTH,"MOV $%04X, %%R%0dh",val,val1);
				break;
			default:
				snprintf(ret,MAX_INSTRUCTION_LENGTH,"UNRECOGNISED INSTRUCTION");
				break;
		}
	}else
		snprintf(ret,MAX_INSTRUCTION_LENGTH,"UNRECOGNISED INSTRUCTION");

	return ret;
}