jb302@36: /* mem.c
jb302@36:  * functions for accessing emulator memory */
jb302@36: #include "mem.h"
jb302@36: 
jb302@36: /* get flag value
jb302@36:  * if invalid flag is requested value is 0 */
jb302@36: BYTE
jb302@36: get_flag(BYTE flag) {
jb302@36:     if (flag > 7) {
jb302@36:         return 0;
jb302@36:     }
jb302@36:     else {
jb302@36:         return GBIT(flags, flag);
jb302@36:     }
jb302@36: }
jb302@36: 
jb302@36: /*  set flag to 0 if on == 0
jb302@36:  *  otherwise set flag to 1 */
jb302@36: void
jb302@36: set_flag(BYTE flag, BYTE on) {
jb302@36:     if (flag <= 7) {
jb302@36:         if (on == 0x00) {
jb302@36:             flags = CBIT(flags, flag);
jb302@36:         }
jb302@36:         else {
jb302@36:             flags = SBIT(flags, flag);
jb302@36:         }
jb302@36:     }
jb302@36: }
jb302@36: 
jb302@36: /* sets zero and parity flags based on content of byte */
jb302@36: void
jb302@36: set_zp(BYTE val){
jb302@36:     if (val == 0) {
jb302@36:         set_flag(Z, 1);
jb302@36:         set_flag(P, 0);
jb302@36:     }
jb302@36:     else {
jb302@36:         /* check parity
jb302@36:          * think of this as folding */
jb302@36:         val ^= val >> 4;
jb302@36:         val ^= val >> 2;
jb302@36:         val ^= val >> 1;
jb302@36:         val &= 1;
jb302@36:         if (val == 0) {
jb302@36:             set_flag(P, 1);
jb302@36:         }
jb302@36:         else {
jb302@36:             set_flag(P, 0);
jb302@36:         }
jb302@36:     }
jb302@36: }
jb302@36: 
jb302@36: WIDE
jb302@36: get_wide(BYTE reg) {
jb302@36:     /* high, low */
jb302@36:     return MWIDE(regs[reg + 4], regs[reg + 12]);
jb302@36: }
jb302@36: 
jb302@36: void
jb302@36: set_wide(BYTE reg, WIDE val) {
jb302@36:     regs[reg + 4] = GHIGH(val); /* high */
jb302@36:     regs[reg + 12] = GLOW(val); /* low */
jb302@36: }
jb302@36: 
jb302@36: void 
jb302@36: inc_pc(BYTE n) {
jb302@36:     if ((regs[PCL] + n) > 0xFF) {
jb302@36:         regs[PCH]++;
jb302@36:     }
jb302@36:     regs[PCL] += n;
jb302@36: }
jb302@36: 
jb302@36: BYTE 
jb302@36: fetch(void) {
jb302@36:     BYTE val = mem[get_wide(PC)];
jb302@36:     inc_pc(1);
jb302@36:     return val;
jb302@36: }
jb302@36: 
jb302@36: WIDE
jb302@36: fetch_wide(void) {
jb302@36:     WIDE val = MWIDE(mem[get_wide(PC)], mem[get_wide(PC) + 1]);
jb302@36:     inc_pc(2);
jb302@36:     return val;
jb302@36: }
jb302@36: 
jb302@36: /* 0b000 = R0
jb302@36:  * 0b001 = R1
jb302@36:  * 0b010 = R2
jb302@36:  * 0b011 = R3
jb302@36:  * 0b100 = DPH
jb302@36:  * 0b101 = DPL
jb302@36:  * 0b110 = SPH
jb302@36:  * 0b111 = SPL */
jb302@36: BYTE 
jb302@36: get_reg(BYTE reg) {
jb302@36:     if (reg < 4) {
jb302@36:         return regs[reg | (get_flag(BS) << 3)];
jb302@36:     }
jb302@36:     else {
jb302@36:         switch (reg) {
jb302@36:             
jb302@36:             case 4:
jb302@36:                 return regs[DPH];
jb302@36:             case 5:
jb302@36:                 return regs[DPL];
jb302@36:             case 6:
jb302@36:                 return regs[SPH];
jb302@36:             case 7:
jb302@36:                 return regs[SPL];
jb302@36:             default:
jb302@36:                 return 0;
jb302@36:         }
jb302@36:     }
jb302@36: }
jb302@36: 
jb302@36: void
jb302@36: set_reg(BYTE reg, BYTE val) {
jb302@36:     if (reg < 4) {
jb302@36:         regs[reg | (get_flag(BS) << 3)] = val;
jb302@36:     }
jb302@36:     else {
jb302@36:         switch (reg) {
jb302@36:             
jb302@36:             case 4:
jb302@36:                 regs[DPH] = val;
jb302@36:                 break;
jb302@36:             case 5:
jb302@36:                 regs[DPL] = val;
jb302@36:                 break;
jb302@36:             case 6:
jb302@36:                 regs[SPH] = val;
jb302@36:                 break;
jb302@36:             case 7:
jb302@36:                 regs[SPL] = val;
jb302@36:                 break;
jb302@36:             default:
jb302@36:                 break;
jb302@36:         }
jb302@36:     }
jb302@36: }