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arduino_8080.ino.8080
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arduino_8080.ino.8080
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//
// Intel 8080 CPU emulation on an Arduino Nano
// derived from Z80PACK
// Copyright 2024, Udo Munk & Thomas Eberhardt
//
// History:
// 04-MAY-2024 Release 1.0 implements a very basic 8080 system
// 06-MAY-2024 Release 1.1 add support for a ROM in flash
// 07-MAY-2024 Release 1.2 move 8080 memory into a FRAM
// 13-MAY-2024 Release 1.2.1 can run MITS Altair BASIC
// 17-MAY-2024 Release 1.3 switch to code minimized CPU from Thomas Eberhardt
// 18-MAY-2024 Release 1.4 read 8080 code from a file on SD into FRAM
// 20-MAY-2024 Release 1.5.1 added interrupt key and register dump for debugging
// 22-MAY-2024 Release 1.6 boot from a disk image on SD
// 13-JUN-2024 Release 1.6.1 power on jump into boot ROM
//
//#define FRAM_DEBUG 1 // enables FRAM debug messages
//#define DEBUG // enables some application debug messages
#include <stdint.h>
#include <SPI.h>
#include "Adafruit_FRAM_SPI.h"
#include "SdFat.h"
// unused analog pin to seed random generator
#define UAP 7
// chip select pin for FRAM (default)
#define FRAM_CS 10
// chip select pin for SD card
#define SD_CS 9
// interrupt pin, interrupt 0 is already used by the SPI stuff
// so we use interrupt 1 at the D3 pin
#define USERINT 3
// data types for the 8080 CPU
typedef uint8_t BYTE;
typedef uint16_t WORD;
// project includes
#include "simcore.h"
#include "memsim.h"
#include "sd-fdc.h"
#include "iosim.h"
#include "config.h"
#if _BYTE_ORDER == _LITTLE_ENDIAN
struct cpu_reg {
union {
struct {
BYTE l;
BYTE h;
};
WORD w;
};
};
#elif _BYTE_ORDER == _BIG_ENDIAN
struct cpu_reg {
union {
struct {
BYTE h;
BYTE l;
};
WORD w;
};
};
#else
#error "Unsupported byte order"
#endif
// 8080 CPU state
struct cpu_state {
struct cpu_reg af; /* primary registers */
struct cpu_reg bc;
struct cpu_reg de;
struct cpu_reg hl;
struct cpu_reg sp; /* stack pointer */
struct cpu_reg pc; /* program counter */
BYTE iff; /* interupt flags */
} cpu_state;
// other global variables
CPUState State = Running; // CPU state
unsigned long tstates = 0; // executed T-states
// Insure FAT16/FAT32 only
SdFat32 SD;
// Precomputed table for fast sign, zero and parity flag calculation
#define _ 0
#define S S_FLAG
#define Z Z_FLAG
#define P P_FLAG
static const BYTE szp_flags[256] = {
/*00*/ Z|P, _, _, P, _, P, P, _,
/*08*/ _, P, P, _, P, _, _, P,
/*10*/ _, P, P, _, P, _, _, P,
/*18*/ P, _, _, P, _, P, P, _,
/*20*/ _, P, P, _, P, _, _, P,
/*28*/ P, _, _, P, _, P, P, _,
/*30*/ P, _, _, P, _, P, P, _,
/*38*/ _, P, P, _, P, _, _, P,
/*40*/ _, P, P, _, P, _, _, P,
/*48*/ P, _, _, P, _, P, P, _,
/*50*/ P, _, _, P, _, P, P, _,
/*58*/ _, P, P, _, P, _, _, P,
/*60*/ P, _, _, P, _, P, P, _,
/*68*/ _, P, P, _, P, _, _, P,
/*70*/ _, P, P, _, P, _, _, P,
/*78*/ P, _, _, P, _, P, P, _,
/*80*/ S, S|P, S|P, S, S|P, S, S, S|P,
/*88*/ S|P, S, S, S|P, S, S|P, S|P, S,
/*90*/ S|P, S, S, S|P, S, S|P, S|P, S,
/*98*/ S, S|P, S|P, S, S|P, S, S, S|P,
/*a0*/ S|P, S, S, S|P, S, S|P, S|P, S,
/*a8*/ S, S|P, S|P, S, S|P, S, S, S|P,
/*b0*/ S, S|P, S|P, S, S|P, S, S, S|P,
/*b8*/ S|P, S, S, S|P, S, S|P, S|P, S,
/*c0*/ S|P, S, S, S|P, S, S|P, S|P, S,
/*c8*/ S, S|P, S|P, S, S|P, S, S, S|P,
/*d0*/ S, S|P, S|P, S, S|P, S, S, S|P,
/*d8*/ S|P, S, S, S|P, S, S|P, S|P, S,
/*e0*/ S, S|P, S|P, S, S|P, S, S, S|P,
/*e8*/ S|P, S, S, S|P, S, S|P, S|P, S,
/*f0*/ S|P, S, S, S|P, S, S|P, S|P, S,
/*f8*/ S, S|P, S|P, S, S|P, S, S, S|P
};
#undef _
#undef S
#undef Z
#undef P
// This function initializes the CPU into the documented
// state. Prevents assumptions about register contents
// of a just powered CPU, like HL is always 0 in the
// beginning, which is not the case with the silicon.
static void init_cpu(struct cpu_state *cpu_state)
{
cpu_state->pc.w = 0xff00; // normally 0, power on jump to boot ROM
cpu_state->sp.w = random(65535);
cpu_state->af.w = random(65535);
cpu_state->bc.w = random(65535);
cpu_state->de.w = random(65535);
cpu_state->hl.w = random(65535);
}
// This function builds the 8080 central processing unit.
// The opcode where PC points to is fetched from the memory
// and PC incremented by one. The opcode is then dispatched
// to execute code, which emulates this 8080 opcode.
//
// For a description of how the arithmetic flags calculation works see:
// http://emulators.com/docs/lazyoverflowdetect_final.pdf
//
// The formula for subtraction carry outs was determined by staring
// intently at some truth tables.
//
// cout contains the carry outs for every bit
void cpu_8080(struct cpu_state *cpu_state)
{
struct cpu_state cpu_regs;
BYTE t, res, cout, P;
struct cpu_reg w; /* working register */
#pragma push_macro("F")
#undef F
#pragma push_macro("SP")
#undef SP
#pragma push_macro("SPH")
#undef SPH
#pragma push_macro("SPL")
#undef SPL
#pragma push_macro("PC")
#undef PC
#define AF cpu_regs.af.w
#define A cpu_regs.af.h
#define F cpu_regs.af.l
#define BC cpu_regs.bc.w
#define B cpu_regs.bc.h
#define C cpu_regs.bc.l
#define DE cpu_regs.de.w
#define D cpu_regs.de.h
#define E cpu_regs.de.l
#define HL cpu_regs.hl.w
#define H cpu_regs.hl.h
#define L cpu_regs.hl.l
#define SP cpu_regs.sp.w
#define SPH cpu_regs.sp.h
#define SPL cpu_regs.sp.l
#define PC cpu_regs.pc.w
#define PCH cpu_regs.pc.h
#define PCL cpu_regs.pc.l
#define IFF cpu_regs.iff
#define W w.w
#define WH w.h
#define WL w.l
cpu_regs = *cpu_state;
do {
t = 4; /* minimum clock cycles for M1 */
switch (memrdr(PC++)) { /* execute next opcode */
case 0x00: /* NOP */
case 0x08: /* NOP* */
case 0x10: /* NOP* */
case 0x18: /* NOP* */
case 0x20: /* NOP* */
case 0x28: /* NOP* */
case 0x30: /* NOP* */
case 0x38: /* NOP* */
break;
case 0x40: /* MOV B,B */
case 0x49: /* MOV C,C */
case 0x52: /* MOV D,D */
case 0x5b: /* MOV E,E */
case 0x64: /* MOV H,H */
case 0x6d: /* MOV L,L */
case 0x7f: /* MOV A,A */
t++;
break;
case 0x01: /* LXI B,nn */
C = memrdr(PC++);
B = memrdr(PC++);
t += 6;
break;
case 0x02: /* STAX B */
memwrt(BC, A);
t += 3;
break;
case 0x03: /* INX B */
BC++;
t++;
break;
case 0x04: /* INR B */
P = B;
res = ++B;
finish_inr:
cout = (P & 1) | ((P | 1) & ~res);
F = ((F & C_FLAG) |
(((cout >> 3) & 1) << H_SHIFT) |
szp_flags[res]);
/* C_FLAG unchanged */
t++;
break;
case 0x05: /* DCR B */
P = B;
res = --B;
finish_dcr:
cout = (~P & 1) | ((~P | 1) & res);
F = ((F & C_FLAG) |
(((cout >> 3) & 1) << H_SHIFT) |
szp_flags[res]);
F ^= H_FLAG;
/* C_FLAG unchanged */
t++;
break;
case 0x06: /* MVI B,n */
B = memrdr(PC++);
t += 3;
break;
case 0x07: /* RLC */
res = ((A & 0x80) >> 7) & 1;
F = (F & ~C_FLAG) | (res << C_SHIFT);
/* S_FLAG, Z_FLAG, H_FLAG, and P_FLAG unchanged */
A = (A << 1) | res;
break;
case 0x09: /* DAD B */
W = HL + BC;
cout = (H & B) | ((H | B) & ~WH);
finish_dad:
F = (F & ~C_FLAG) | (((cout >> 7) & 1) << C_SHIFT);
/* S_FLAG, Z_FLAG, H_FLAG, and P_FLAG unchanged */
H = WH;
L = WL;
t += 6;
break;
case 0x0a: /* LDAX B */
A = memrdr(BC);
t += 3;
break;
case 0x0b: /* DCX B */
BC--;
t++;
break;
case 0x0c: /* INR C */
P = C;
res = ++C;
goto finish_inr;
case 0x0d: /* DCR C */
P = C;
res = --C;
goto finish_dcr;
case 0x0e: /* MVI C,n */
C = memrdr(PC++);
t += 3;
break;
case 0x0f: /* RRC */
res = A & 1;
F = (F & ~C_FLAG) | (res << C_SHIFT);
/* S_FLAG, Z_FLAG, H_FLAG, and P_FLAG unchanged */
A = (A >> 1) | (res << 7);
break;
case 0x11: /* LXI D,nn */
E = memrdr(PC++);
D = memrdr(PC++);
t += 6;
break;
case 0x12: /* STAX D */
memwrt(DE, A);
t += 3;
break;
case 0x13: /* INX D */
DE++;
t++;
break;
case 0x14: /* INR D */
P = D;
res = ++D;
goto finish_inr;
case 0x15: /* DCR D */
P = D;
res = --D;
goto finish_dcr;
case 0x16: /* MVI D,n */
D = memrdr(PC++);
t += 3;
break;
case 0x17: /* RAL */
res = (F >> C_SHIFT) & 1;
F = (F & ~C_FLAG) | ((((A & 0x80) >> 7) & 1) << C_SHIFT);
/* S_FLAG, Z_FLAG, H_FLAG, and P_FLAG unchanged */
A = (A << 1) | res;
break;
case 0x19: /* DAD D */
W = HL + DE;
cout = (H & D) | ((H | D) & ~WH);
goto finish_dad;
case 0x1a: /* LDAX D */
A = memrdr(DE);
t += 3;
break;
case 0x1b: /* DCX D */
DE--;
t++;
break;
case 0x1c: /* INR E */
P = E;
res = ++E;
goto finish_inr;
case 0x1d: /* DCR E */
P = E;
res = --E;
goto finish_dcr;
case 0x1e: /* MVI E,n */
E = memrdr(PC++);
t += 3;
break;
case 0x1f: /* RAR */
res = (F >> C_SHIFT) & 1;
F = (F & ~C_FLAG) | ((A & 1) << C_SHIFT);
/* S_FLAG, Z_FLAG, H_FLAG, and P_FLAG unchanged */
A = (A >> 1) | (res << 7);
break;
case 0x21: /* LXI H,nn */
L = memrdr(PC++);
H = memrdr(PC++);
t += 6;
break;
case 0x22: /* SHLD nn */
WL = memrdr(PC++);
WH = memrdr(PC++);
memwrt(W, L);
memwrt(W + 1, H);
t += 12;
break;
case 0x23: /* INX H */
HL++;
t++;
break;
case 0x24: /* INR H */
P = H;
res = ++H;
goto finish_inr;
case 0x25: /* DCR H */
P = H;
res = --H;
goto finish_dcr;
case 0x26: /* MVI H,n */
H = memrdr(PC++);
t += 3;
break;
case 0x27: /* DAA */
P = 0;
if (((A & 0xf) > 9) || (F & H_FLAG))
P |= 0x06;
if ((A > 0x99) || (F & C_FLAG)) {
F |= C_FLAG;
P |= 0x60;
}
res = A + P;
cout = (A & P) | ((A | P) & ~res);
F = ((F & C_FLAG) |
(((cout >> 3) & 1) << H_SHIFT) |
szp_flags[res]);
A = res;
break;
case 0x29: /* DAD H */
W = HL << 1;
cout = H | (H & ~WH);
goto finish_dad;
case 0x2a: /* LHLD nn */
WL = memrdr(PC++);
WH = memrdr(PC++);
L = memrdr(W);
H = memrdr(W + 1);
t += 12;
break;
case 0x2b: /* DCX H */
HL--;
t++;
break;
case 0x2c: /* INR L */
P = L;
res = ++L;
goto finish_inr;
case 0x2d: /* DCR L */
P = L;
res = --L;
goto finish_dcr;
case 0x2e: /* MVI L,n */
L = memrdr(PC++);
t += 3;
break;
case 0x2f: /* CMA */
A = ~A;
break;
case 0x31: /* LXI SP,nn */
SPL = memrdr(PC++);
SPH = memrdr(PC++);
t += 6;
break;
case 0x32: /* STA nn */
WL = memrdr(PC++);
WH = memrdr(PC++);
memwrt(W, A);
t += 9;
break;
case 0x33: /* INX SP */
SP++;
t++;
break;
case 0x34: /* INR M */
P = memrdr(HL);
res = P + 1;
memwrt(HL, res);
t += 5;
goto finish_inr;
case 0x35: /* DCR M */
P = memrdr(HL);
res = P - 1;
memwrt(HL, res);
t += 5;
goto finish_dcr;
case 0x36: /* MVI M,n */
memwrt(HL, memrdr(PC++));
t += 6;
break;
case 0x37: /* STC */
F |= C_FLAG;
/* S_FLAG, Z_FLAG, H_FLAG, and P_FLAG unchanged */
break;
case 0x39: /* DAD SP */
W = HL + SP;
cout = (H & SPH) | ((H | SPH) & ~WH);
goto finish_dad;
case 0x3a: /* LDA nn */
WL = memrdr(PC++);
WH = memrdr(PC++);
A = memrdr(W);
t += 9;
break;
case 0x3b: /* DCX SP */
SP--;
t++;
break;
case 0x3c: /* INR A */
P = A;
res = ++A;
goto finish_inr;
case 0x3d: /* DCR A */
P = A;
res = --A;
goto finish_dcr;
case 0x3e: /* MVI A,n */
A = memrdr(PC++);
t += 3;
break;
case 0x3f: /* CMC */
F ^= C_FLAG;
/* S_FLAG, Z_FLAG, H_FLAG, and P_FLAG unchanged */
break;
case 0x41: /* MOV B,C */
B = C;
t++;
break;
case 0x42: /* MOV B,D */
B = D;
t++;
break;
case 0x43: /* MOV B,E */
B = E;
t++;
break;
case 0x44: /* MOV B,H */
B = H;
t++;
break;
case 0x45: /* MOV B,L */
B = L;
t++;
break;
case 0x46: /* MOV B,M */
B = memrdr(HL);
t += 3;
break;
case 0x47: /* MOV B,A */
B = A;
t++;
break;
case 0x48: /* MOV C,B */
C = B;
t++;
break;
case 0x4a: /* MOV C,D */
C = D;
t++;
break;
case 0x4b: /* MOV C,E */
C = E;
t++;
break;
case 0x4c: /* MOV C,H */
C = H;
t++;
break;
case 0x4d: /* MOV C,L */
C = L;
t++;
break;
case 0x4e: /* MOV C,M */
C = memrdr(HL);
t += 3;
break;
case 0x4f: /* MOV C,A */
C = A;
t++;
break;
case 0x50: /* MOV D,B */
D = B;
t++;
break;
case 0x51: /* MOV D,C */
D = C;
t++;
break;
case 0x53: /* MOV D,E */
D = E;
t++;
break;
case 0x54: /* MOV D,H */
D = H;
t++;
break;
case 0x55: /* MOV D,L */
D = L;
t++;
break;
case 0x56: /* MOV D,M */
D = memrdr(HL);
t += 3;
break;
case 0x57: /* MOV D,A */
D = A;
t++;
break;
case 0x58: /* MOV E,B */
E = B;
t++;
break;
case 0x59: /* MOV E,C */
E = C;
t++;
break;
case 0x5a: /* MOV E,D */
E = D;
t++;
break;
case 0x5c: /* MOV E,H */
E = H;
t++;
break;
case 0x5d: /* MOV E,L */
E = L;
t++;
break;
case 0x5e: /* MOV E,M */
E = memrdr(HL);
t += 3;
break;
case 0x5f: /* MOV E,A */
E = A;
t++;
break;
case 0x60: /* MOV H,B */
H = B;
t++;
break;
case 0x61: /* MOV H,C */
H = C;
t++;
break;
case 0x62: /* MOV H,D */
H = D;
t++;
break;
case 0x63: /* MOV H,E */
H = E;
t++;
break;
case 0x65: /* MOV H,L */
H = L;
t++;
break;
case 0x66: /* MOV H,M */
H = memrdr(HL);
t += 3;
break;
case 0x67: /* MOV H,A */
H = A;
t++;
break;
case 0x68: /* MOV L,B */
L = B;
t++;
break;
case 0x69: /* MOV L,C */
L = C;
t++;
break;
case 0x6a: /* MOV L,D */
L = D;
t++;
break;
case 0x6b: /* MOV L,E */
L = E;
t++;
break;
case 0x6c: /* MOV L,H */
L = H;
t++;
break;
case 0x6e: /* MOV L,M */
L = memrdr(HL);
t += 3;
break;
case 0x6f: /* MOV L,A */
L = A;
t++;
break;
case 0x70: /* MOV M,B */
memwrt(HL, B);
t += 3;
break;
case 0x71: /* MOV M,C */
memwrt(HL, C);
t += 3;
break;
case 0x72: /* MOV M,D */
memwrt(HL, D);
t += 3;
break;
case 0x73: /* MOV M,E */
memwrt(HL, E);
t += 3;
break;
case 0x74: /* MOV M,H */
memwrt(HL, H);
t += 3;
break;
case 0x75: /* MOV M,L */
memwrt(HL, L);
t += 3;
break;
case 0x76: /* HLT */
// cry and die, no interrupts yet
State = Halted;
t += 3;
break;
case 0x77: /* MOV M,A */
memwrt(HL, A);
t += 3;
break;
case 0x78: /* MOV A,B */
A = B;
t++;
break;
case 0x79: /* MOV A,C */
A = C;
t++;
break;
case 0x7a: /* MOV A,D */
A = D;
t++;
break;
case 0x7b: /* MOV A,E */
A = E;
t++;
break;
case 0x7c: /* MOV A,H */
A = H;
t++;
break;
case 0x7d: /* MOV A,L */
A = L;
t++;
break;
case 0x7e: /* MOV A,M */
A = memrdr(HL);
t += 3;
break;
case 0x80: /* ADD B */
P = B;
res = 0;
finish_add:
res = A + P + res;
cout = (A & P) | ((A | P) & ~res);
F = ((((cout >> 7) & 1) << C_SHIFT) |
(((cout >> 3) & 1) << H_SHIFT) |
szp_flags[res]);
A = res;
break;
case 0x81: /* ADD C */
P = C;
res = 0;
goto finish_add;
case 0x82: /* ADD D */
P = D;
res = 0;
goto finish_add;
case 0x83: /* ADD E */
P = E;
res = 0;
goto finish_add;
case 0x84: /* ADD H */
P = H;
res = 0;
goto finish_add;
case 0x85: /* ADD L */
P = L;
res = 0;
goto finish_add;
case 0x86: /* ADD M */
P = memrdr(HL);
res = 0;
t += 3;
goto finish_add;
case 0x87: /* ADD A */
P = A;
res = 0;
goto finish_add;
case 0x88: /* ADC B */
P = B;
res = (F >> C_SHIFT) & 1;
goto finish_add;
case 0x89: /* ADC C */
P = C;
res = (F >> C_SHIFT) & 1;
goto finish_add;
case 0x8a: /* ADC D */
P = D;
res = (F >> C_SHIFT) & 1;
goto finish_add;
case 0x8b: /* ADC E */
P = E;
res = (F >> C_SHIFT) & 1;
goto finish_add;
case 0x8c: /* ADC H */
P = H;
res = (F >> C_SHIFT) & 1;
goto finish_add;
case 0x8d: /* ADC L */
P = L;
res = (F >> C_SHIFT) & 1;
goto finish_add;
case 0x8e: /* ADC M */
P = memrdr(HL);
res = (F >> C_SHIFT) & 1;
t += 3;
goto finish_add;
case 0x8f: /* ADC A */
P = A;
res = (F >> C_SHIFT) & 1;
goto finish_add;
case 0x90: /* SUB B */
P = B;
res = 0;
finish_sub:
res = A - P - res;
cout = (~A & P) | ((~A | P) & res);
F = ((((cout >> 7) & 1) << C_SHIFT) |
(((cout >> 3) & 1) << H_SHIFT) |
szp_flags[res]);
F ^= H_FLAG;
A = res;
break;
case 0x91: /* SUB C */
P = C;
res = 0;
goto finish_sub;
case 0x92: /* SUB D */
P = D;
res = 0;
goto finish_sub;
case 0x93: /* SUB E */
P = E;
res = 0;
goto finish_sub;
case 0x94: /* SUB H */
P = H;
res = 0;
goto finish_sub;
case 0x95: /* SUB L */
P = L;
res = 0;
goto finish_sub;
case 0x96: /* SUB M */
P = memrdr(HL);
res = 0;
t += 3;
goto finish_sub;
case 0x97: /* SUB A */
F = Z_FLAG | H_FLAG | P_FLAG;
/* S_FLAG and C_FLAG cleared */
A = 0;
break;
case 0x98: /* SBB B */
P = B;
res = (F >> C_SHIFT) & 1;
goto finish_sub;
case 0x99: /* SBB C */
P = C;
res = (F >> C_SHIFT) & 1;
goto finish_sub;