void mySendFrame(unsigned char* databuff, int size) {//add crc and cooperate with physical layer. databuff should be ready to send. size shoule be without crc
if (databuff[0] != FRAME_NAK) {
//piggyback ack
short i = (receiverLeft - 1) % windowSize;//log the last ack arrived
if (i < 0)
i += windowSize;
for (short j = 0; j < bufferSize; j++) {
if (receiver[(receiverLeft + j) % bufferSize].frameArrived)
i = (receiverLeft + j) % windowSize;
else break;
}
databuff[0] == FRAME_DATA ? databuff[2] = i : databuff[1] = i;
}
//append crc
*(unsigned int*)(databuff + size) = crc32(databuff, size);
size += 4;//add length
if (databuff[0] == FRAME_DATA)
//add timer
start_timer(databuff[1], retimer);
//piggyback ack timer
if (databuff[0] != FRAME_NAK) {
stop_ack_timer();
start_ack_timer(acktimer);
}
send_frame(databuff, size);
}
static void send_ack_frame(void)
{
struct FRAME s;
s.kind = FRAME_ACK;
s.ack = (frame_expected + MAX_SEQ)%(MAX_SEQ + 1);
dbg_frame("Send ACK %d\n", s.ack);
put_frame((unsigned char *)&s, 3);
stop_ack_timer();
}
static void send_frame(frame_kind fk, seq_nr frame_nr, seq_nr frame_expected, packet buffer[])
{
/* Construct and send a data, ack, or nak frame. */
frame s; /* scratch variable */
s.kind = fk; /* kind == data, ack, or nak */
if (fk == data) s.info = buffer[frame_nr % NR_BUFS];
s.seq = frame_nr; /* only meaningful for data frames */
s.ack = (frame_expected + MAX_SEQ) % (MAX_SEQ + 1);
if (fk == nak) no_nak = false; /* one nak per frame, please */
to_physical_layer(&s); /* transmit the frame */
if (fk == data) start_timer(frame_nr % NR_BUFS);
stop_ack_timer(); /* no need for separate ack frame */
}
static void send_data_frame(void)
{
struct FRAME s;
s.kind = FRAME_DATA;
s.seq = next_frame_to_send;
s.ack = (frame_expected + MAX_SEQ) % (MAX_SEQ + 1);
memcpy(s.data, buffer[next_frame_to_send], PKT_LEN);
dbg_frame("Send DATA %d %d, ID %d\n", s.seq, s.ack, *(short *)s.data);
put_frame((unsigned char *)&s, 3 + PKT_LEN); // the extra 3 bytes are ack,kind,seq
start_timer(next_frame_to_send, DATA_TIMER);
stop_ack_timer();
}
