void *ax25_frame(uint8_t *frame, int *length, char *scallsign, char sssid, char *dcallsign, char dssid, char ttl1, char ttl2, char *data, ...)
{
uint8_t *s, j;
uint16_t CRC;
va_list va;
va_start(va, data);
/* Write in the callsigns and paths */
s = _ax25_callsign(frame, dcallsign, dssid);
s = _ax25_callsign(s, scallsign, sssid);
if (ttl1) s = _ax25_callsign(s, "WIDE1", ttl1);
if (ttl2) s = _ax25_callsign(s, "WIDE2", ttl2);
/* Mark the end of the callsigns */
s[-1] |= 1;
*(s++) = 0x03; /* Control, 0x03 = APRS-UI frame */
*(s++) = 0xF0; /* Protocol ID: 0xF0 = no layer 3 data */
// printf ("Length A is %d\n", s - frame);
// printf ("Adding %d bytes\n",
vsnprintf((char *) s, 200 - (s - frame) - 2, data, va);
va_end(va);
// printf ("Length B is %d\n", strlen(frame));
// Calculate and append the checksum
for (CRC=0xffff, s=frame; *s; s++)
{
CRC ^= ((unsigned int)*s);
for (j=0; j<8; j++)
{
if (CRC & 1)
{
CRC = (CRC >> 1) ^ 0x8408;
}
else
{
CRC >>= 1;
}
}
void ax25_frame(char *scallsign, char sssid, char *dcallsign, char dssid,
char *path1, char ttl1, char *path2, char ttl2, char *data, ...)
{
static uint8_t frame[100];
uint8_t *s;
uint16_t x;
va_list va;
va_start(va, data);
/* Pause while there is still data transmitting */
while(_txlen);
/* Write in the callsigns and paths */
s = _ax25_callsign(frame, dcallsign, dssid);
s = _ax25_callsign(s, scallsign, sssid);
if(path1) s = _ax25_callsign(s, path1, ttl1);
if(path2) s = _ax25_callsign(s, path2, ttl2);
/* Mark the end of the callsigns */
s[-1] |= 1;
*(s++) = 0x03; /* Control, 0x03 = APRS-UI frame */
*(s++) = 0xF0; /* Protocol ID: 0xF0 = no layer 3 data */
vsnprintf((char *) s, 100 - (s - frame) - 2, data, va);
va_end(va);
/* Calculate and append the checksum */
for(x = 0xFFFF, s = frame; *s; s++)
x = _crc_ccitt_update(x, *s);
*(s++) = ~(x & 0xFF);
*(s++) = ~((x >> 8) & 0xFF);
/* Point the interrupt at the data to be transmit */
_txbuf = frame;
_txlen = s - frame;
/* Enable the timer and key the radio */
TIMSK2 |= _BV(TOIE2);
PORTA |= TXENABLE;
}
