Intel 8080 Emulator

Overview

This project implements an I8080A emulator in C. It handles all 256 opcodes, including illegal ones. It also counts cycles and has an interrupt system.

Usage

Setup

Include <i8080.h> and create a new instance of i8080_cpu_t. Then call i8080_init in order to initalize the processor.

#include <i8080.h>

i8080_cpu_t cpu;
i8080_init(&cpu, &cpu, rb, wb, inb, outb);

User Defined Functions

To allow for the most flexibility, the behaviour of memory and I/O are left up to the user. Define read byte, write byte, input byte, and output byte functions. Then give these functions to the emulator by passing them as pointers to i8080_init.

uint8_t rb(void *userptr, uint16_t addr) {
    // implement read byte
}

void wb(void *userptr, uint16_t addr, uint8_t val) {
    // implement write byte
}

uint8_t inb(void *userptr, uint8_t port) {
    // implement in byte
}

void outb(void *userptr, uint8_t port, uint8_t val) {
    // implement out byte
}

// pass the function pointers
i8080_init(&cpu, /*userdata*/, rb, wb, inb, outb);

The second arguement of i8080_init can be used to input user defined data that can be acessed by user functions.

Running

Call the i8080_step function to run the emulator. You can check if the processor has halted by acessing cpu.hlt.

while (!cpu.hlt) {
    i8080_step(&cpu);
}

Interrupts

The I8080A implements an interrupt system. To request an interrupt, call the i8080_interrupt function with the opcode of the instruction you would like to be called (usually this is a RST instruction).

#include <i8080.h>

i8080_interrupt(&cpu, RST_0);

Cycles

Cycles are useful for timing purposes. This emulator is cycle accurate. The amount of total cycles that have been executed are stored in cpu.cycles.

Debugging

You may want to see the values of the registers and memory for debugging purposes. This emulator provides the following functions:

• i8080_dump_registers
  • Prints the values of registers and register pairs
• i8080_dump_stack
  • Prints the first ten values on the stack
• i8080_dump_memory
  • Prints a page of memory (256 bytes)
  • The second arguement decides the page of memory to be printed

Accuracy

This emulator should be accurate enough for most applications. It is capable of executing all 8080 instructions, including illegal opcodes. It implements cycle counting for more precise timings.

Tests

Here are the tests use to verify the behavior of the emulator:

• Preliminary Z80 Tests by Frank D. Cringle (modified for Intel 8080 by Ian Bartholomew)
• 8080/8085 CPU Diagnostic by Microcosm Associates
• Supersoft Associates CPU Test
• 8080/8085 Exerciser "Modified"

Results

This is the listing of the results from running test.c, which goes through each test suite.

BEGINNING TEST roms/8080PRE.COM
8080 Preliminary tests complete
TEST roms/8080PRE.COM RESULTS
        Instructions Executed: 1061
        Cycles Executed: 7817
        Time Elapsed: 0.000012
        Speed (MIPS): 88.416667
        Speed (MHz): 651.416667
BEGINNING TEST roms/TST8080.COM
MICROCOSM ASSOCIATES 8080/8085 CPU DIAGNOSTIC
 VERSION 1.0  (C) 1980

 CPU IS OPERATIONAL
TEST roms/TST8080.COM RESULTS
        Instructions Executed: 651
        Cycles Executed: 4924
        Time Elapsed: 0.000042
        Speed (MIPS): 15.500000
        Speed (MHz): 117.238095
BEGINNING TEST roms/CPUTEST.COM

DIAGNOSTICS II V1.2 - CPU TEST
COPYRIGHT (C) 1981 - SUPERSOFT ASSOCIATES

ABCDEFGHIJKLMNOPQRSTUVWXYZ
CPU IS 8080/8085
BEGIN TIMING TEST
END TIMING TEST
CPU TESTS OK

TEST roms/CPUTEST.COM RESULTS
        Instructions Executed: 33971311
        Cycles Executed: 255653383
        Time Elapsed: 0.284545
        Speed (MIPS): 119.388185
        Speed (MHz): 898.463804
BEGINNING TEST roms/8080EXM.COM
8080 instruction exerciser
dad <b,d,h,sp>................  PASS! crc is:14474ba6
aluop nn......................  PASS! crc is:9e922f9e
aluop <b,c,d,e,h,l,m,a>.......  PASS! crc is:cf762c86
<daa,cma,stc,cmc>.............  PASS! crc is:bb3f030c
<inr,dcr> a...................  PASS! crc is:adb6460e
<inr,dcr> b...................  PASS! crc is:83ed1345
<inx,dcx> b...................  PASS! crc is:f79287cd
<inr,dcr> c...................  PASS! crc is:e5f6721b
<inr,dcr> d...................  PASS! crc is:15b5579a
<inx,dcx> d...................  PASS! crc is:7f4e2501
<inr,dcr> e...................  PASS! crc is:cf2ab396
<inr,dcr> h...................  PASS! crc is:12b2952c
<inx,dcx> h...................  PASS! crc is:9f2b23c0
<inr,dcr> l...................  PASS! crc is:ff57d356
<inr,dcr> m...................  PASS! crc is:92e963bd
<inx,dcx> sp..................  PASS! crc is:d5702fab
lhld nnnn.....................  PASS! crc is:a9c3d5cb
shld nnnn.....................  PASS! crc is:e8864f26
lxi <b,d,h,sp>,nnnn...........  PASS! crc is:fcf46e12
ldax <b,d>....................  PASS! crc is:2b821d5f
mvi <b,c,d,e,h,l,m,a>,nn......  PASS! crc is:eaa72044
mov <bcdehla>,<bcdehla>.......  PASS! crc is:10b58cee
sta nnnn / lda nnnn...........  PASS! crc is:ed57af72
<rlc,rrc,ral,rar>.............  PASS! crc is:e0d89235
stax <b,d>....................  PASS! crc is:2b0471e9
Tests complete
TEST roms/8080EXM.COM RESULTS
        Instructions Executed: 2919050698
        Cycles Executed: 23803381171
        Time Elapsed: 23.672660
        Speed (MIPS): 123.308944
        Speed (MHz): 1005.522031

Resources

Here is a list of resources used to make this emulator:

Datasheets

• The 8080 Central Processor Unit

• 8080 Assembly Language Programming Manual

Tables

• Tobias V. Langhoff's Intel 8080/8085 opcode table

• Intel 8080 instruction set

Emulators

• 8080 by superzazu
• m8080 by Pedro Minicz
• Intel 8080 Emulator by nav97

Other

• Intel 8080