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#include "framing.h"
static inline bool is_cmd(uint8_t byte) {
return (byte == FRAME_START || byte == FRAME_STOP || byte == FRAME_ESCAPE);
}
static inline void reset(framer* f) {
f->position = -1;
f->checksum = 0x00;
}
static inline void accept(framer* f, uint8_t byte) {
//if a new byte would cause an overflow, restart frame
//note that this should not happen if both communicating parties have defined the same maximum frame length
if (f->position >= MAX_FRAME_SIZE) {
reset(f);
return;
}
if (f->position != -1) { // i.e. a previous byte exists
f->buffer[f->position] = f->staged;
f->checksum = f->checksum ^ f->staged;
}
f->position += 1;
f->staged = byte;
}
void receive_byte(framer* f, uint8_t byte) {
switch(f->state) {
case ESCAPING:
accept(f, byte);
f->state = RECEIVING;
break;
case WAITING:
if (byte == FRAME_START) {
reset(f);
f->state = RECEIVING;
}
break;
case RECEIVING:
switch(byte) {
case FRAME_ESCAPE:
f->state = ESCAPING;
break;
case FRAME_START:
reset(f);
break;
case FRAME_STOP:
f->state = WAITING;
if (f->staged == f->checksum) { //at this point, staged byte is the checksum sent in the frame (last byte of frame)
f->receiver(f->position, f->buffer);
}
break;
default:
accept(f, byte);
break;
}
}
}
void send_frame(framer* f, int16_t size, const uint8_t * const data_out) {
uint8_t checksum = 0x00;
uint8_t byte;
send_byte_function sender = f->sender;
sender(FRAME_START);
int i;
for (i = 0; i < size; ++i) {
byte = data_out[i];
if (is_cmd(byte)) sender(FRAME_ESCAPE);
sender(byte);
checksum = checksum ^ byte;
}
if (is_cmd(checksum)) sender(FRAME_ESCAPE);
sender(checksum);
sender(FRAME_STOP);
}
void init_framer(framer* f) {
f->state = WAITING;
reset(f);
}
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