Comments (6)
from 6502.
Yes. It's very easy. The m6502_power()
sets the registers to the values they would be after a real CPU is powered ON (or OFF).
Passing state
as TRUE
initializes the registers with the values after power ON. Passing FALSE
clears the registers (that's good to show them as 0
in a debugger, for example).
The following example emulates a fictional machine. A linear video framebuffer is assumed to be located at address F000h
, with indexed colors, palette of 16 colors, 1 byte per index. The machine produces an IRQ during the VBLANK interval:
#define MACHINE_SCREEN_WIDTH 352
#define MACHINE_SCREEN_HEIGHT 296
#define MACHINE_VISIBLE_SCANLINES MACHINE_SCREEN_HEIGHT
#define MACHINE_VBLANK_SCANLINES 16
#define MACHINE_VRAM_ADDRESS 0xF000
#define MACHINE_CYCLES_PER_FRAME 69888
#define MACHINE_CYCLES_PER_IRQ 32
#define MACHINE_CYCLES_PER_SCANLINE \
(MACHINE_CYCLES_PER_FRAME / (MACHINE_VISIBLE_SCANLINES + MACHINE_VBLANK_SCANLINES))
#define MACHINE_CYCLES_PER_VBLANK \
(MACHINE_CYCLES_PER_SCANLINE * MACHINE_VBLANK_SCANLINES)
#define MACHINE_CYCLES_AT_IRQ 24
#define MACHINE_CYCLES_AT_IRQ_END (MACHINE_CYCLES_AT_IRQ + MACHINE_CYCLES_PER_IRQ)
#define MACHINE_CYCLES_AT_VISIBLE_SCANLINES MACHINE_CYCLES_PER_VBLANK
#define RGBA(r, g, b) 0x##FF##b##g##r
zuint32 const color_palette[16] = {
RGBA(00, 00, 00), RGBA(00, 00, D7), RGBA(D7, 00, 00), RGBA(D7, 00, D7),
RGBA(00, D7, 00), RGBA(00, D7, D7), RGBA(D7, D7, 00), RGBA(D7, D7, D7),
RGBA(00, 00, 00), RGBA(00, 00, FF), RGBA(FF, 00, 00), RGBA(FF, 00, FF),
RGBA(00, FF, 00), RGBA(00, FF, FF), RGBA(FF, FF, 00), RGBA(FF, FF, FF)
};
typedef struct {
M6502 cpu;
zuint8 memory[65535];
zusize frame_cycles;
zuint32 *video_output_buffer;
} Machine;
zuint8 cpu_read(Machine *self, zuint16 address)
{return self->memory[address];}
void cpu_write(Machine *self, zuint16 address, zuint8 value)
{self->memory[address] = value;}
void machine_initialize(Machine *self, zuint32 *video_output_buffer)
{
self->cpu.context = self;
self->cpu.read = cpu_read;
self->cpu.write = cpu_write;
m6502_power(&self->cpu, TRUE);
memset(self->memory, 0, 65535);
self->video_output_buffer = video_output_buffer;
self->cycles = 0;
}
void machine_run_frame(Machine *self)
{
zuint y, x;
zuint8* vram_input = &self->memory[MACHINE_VRAM_ADDRESS];
zuint32* video_output = self->video_output_buffer;
/* VBLANK before IRQ */
self->cycles += m6502_run(&self->cpu, MACHINE_CYCLES_AT_IRQ - self->cycles);
/* IRQ */
m6502_irq(&self->cpu, TRUE);
self->cycles += m6502_irq(&self->cpu, MACHINE_CYCLES_AT_IRQ_END - self->cycles);
m6502_irq(&self->cpu, FALSE);
/* VBLANK after IRQ */
self->cycles += m6502_run(&self->cpu, MACHINE_CYCLES_AT_VISIBLE_SCANLINES - self->cycles);
/* Visible scanlines */
for (y = 0; y < MACHINE_VISIBLE_SCANLINES; y++)
{
self->cycles = m6502_run(
&self->cpu,
MACHINE_CYCLES_AT_VISIBLE_SCANLINES +
((y + 1) * MACHINE_CYCLES_PER_SCANLINE) -
self->cycles);
/* Draw scanline pixels in the output buffer */
for (x = 0; x < MACHINE_SCREEN_WIDTH; x++)
*video_output++ = color_palette[*vram_input++];
}
self->cycles -= MACHINE_CYCLES_PER_FRAME;
}
int main(int argc, char *argv)
{
zuint32 video_buffer[MACHINE_SCREEN_WIDTH * MACHINE_SCREEN_HEIGHT];
Machine machine;
machine_initialize(&machine, video_buffer);
while (1)
{
machine_run_frame(&machine);
/* Draw frame */
...
}
return 0;
}
from 6502.
If you have more doubts, feel free to join my Discord server:
https://discord.gg/NeTytxBh
The link will be valid for 7 days.
from 6502.
main.c:35:15: error: invalid operands to binary expression ('size_t' (aka 'unsigned long') and 'void')
self->cycles += m6502_irq(&self->cpu, MACHINE_CYCLES_AT_IRQ_END - self->cycles);
~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
from 6502.
This code could indeed use a "simple emulator" framework that can be used with the CPU backend. Possibly this could also be used for the Z80 backend, as they function similarly.
from 6502.
I have another example for the Z80 documentation: https://zxe.io/software/Z80/documentation/latest/Usage.html
The documentation is not finished yet, but it will be soon.
from 6502.
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from 6502.