segatools/board/sg-frame.c
2018-11-23 14:37:42 -05:00

166 lines
3.4 KiB
C

#include <windows.h>
#include <assert.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include "board/sg-frame.h"
#include "hook/iobuf.h"
#include "util/dprintf.h"
static HRESULT sg_frame_accept(struct iobuf *dest);
static HRESULT sg_frame_encode_byte(struct iobuf *dest, uint8_t byte);
/* Frame structure:
[0] Sync byte (0xE0)
[1] Frame size (including self)
[2] Address
[3] Sequence no
... Body
[n] Checksum: Sum of all non-framing bytes
Byte stuffing:
0xD0 is an escape byte. Un-escape the subsequent byte by adding 1. */
static HRESULT sg_frame_accept(struct iobuf *dest)
{
uint8_t checksum;
size_t i;
if (dest->pos < 1 || dest->pos != dest->bytes[0] + 1) {
dprintf("SG Frame: Size mismatch\n");
return S_FALSE;
}
checksum = 0;
for (i = 0 ; i < dest->pos - 1 ; i++) {
checksum += dest->bytes[i];
}
if (checksum != dest->bytes[dest->pos - 1]) {
dprintf("SG Frame: Checksum mismatch\n");
return HRESULT_FROM_WIN32(ERROR_CRC);
}
/* Discard checksum */
dest->pos--;
return S_OK;
}
HRESULT sg_frame_decode(struct iobuf *dest, const uint8_t *bytes, size_t nbytes)
{
uint8_t byte;
size_t i;
assert(dest != NULL);
assert(dest->bytes != NULL || dest->nbytes == 0);
assert(dest->pos <= dest->nbytes);
assert(bytes != NULL);
if (nbytes < 1 || bytes[0] != 0xE0) {
dprintf("SG Frame: Bad sync\n");
return E_FAIL;
}
dest->pos = 0;
i = 1;
while (i < nbytes) {
if (dest->pos >= dest->nbytes) {
return HRESULT_FROM_WIN32(ERROR_INSUFFICIENT_BUFFER);
}
byte = bytes[i++];
if (byte == 0xE0) {
dprintf("SG Frame: Unescaped sync\n");
return E_FAIL;
} else if (byte == 0xD0) {
if (i >= nbytes) {
dprintf("SG Frame: Trailing escape\n");
return E_FAIL;
}
byte = bytes[i++];
dest->bytes[dest->pos++] = byte + 1;
} else {
dest->bytes[dest->pos++] = byte;
}
}
return sg_frame_accept(dest);
}
HRESULT sg_frame_encode(
struct iobuf *dest,
const void *ptr,
size_t nbytes)
{
const uint8_t *src;
uint8_t checksum;
uint8_t byte;
size_t i;
HRESULT hr;
assert(dest != NULL);
assert(dest->bytes != NULL || dest->nbytes == 0);
assert(dest->pos <= dest->nbytes);
assert(ptr != NULL);
src = ptr;
assert(nbytes != 0 && src[0] == nbytes);
if (dest->pos >= dest->nbytes) {
return HRESULT_FROM_WIN32(ERROR_INSUFFICIENT_BUFFER);
}
dest->bytes[dest->pos++] = 0xE0;
checksum = 0;
for (i = 0 ; i < nbytes ; i++) {
byte = src[i];
checksum += byte;
hr = sg_frame_encode_byte(dest, byte);
if (FAILED(hr)) {
return hr;
}
}
return sg_frame_encode_byte(dest, checksum);
}
static HRESULT sg_frame_encode_byte(struct iobuf *dest, uint8_t byte)
{
if (byte == 0xD0 || byte == 0xE0) {
if (dest->pos + 2 > dest->nbytes) {
return HRESULT_FROM_WIN32(ERROR_INSUFFICIENT_BUFFER);
}
dest->bytes[dest->pos++] = 0xD0;
dest->bytes[dest->pos++] = byte - 1;
} else {
if (dest->pos + 1 > dest->nbytes) {
return HRESULT_FROM_WIN32(ERROR_INSUFFICIENT_BUFFER);
}
dest->bytes[dest->pos++] = byte;
}
return S_OK;
}