int
l_ping (GPPort *p, GPContext *c)
{
return (l_ping_rec (p, 0));
}
static int
l_ping_rec (GPPort *p, unsigned int level)
{
unsigned char c;
/* Write ENQ and read the response. */
c = ENQ;
CHECK (gp_port_write (p, &c, 1));
CHECK (gp_port_read (p, &c, 1));
switch (c) {
case ACK:
return (GP_OK);
case NACK:
/*
* Uh, lets try again a couple of times, but
* make sure we don't recurse forever.
*/
if (level < 30)
return (l_ping_rec (p, level + 1));
else
return (GP_ERROR_CORRUPTED_DATA);
case ENQ:
/*
* ENQ received. It seems that the camera would like
* to send us data, but we do not want it and
* therefore simply reject it. The camera will try
* two more times with ENQ to get us to receive data
* before finally giving up and sending us ACK.
*/
/* Write NACK. */
c = NACK;
CHECK (gp_port_write (p, &c, 1));
for (;;) {
CHECK (gp_port_read (p, &c, 1));
switch (c) {
case ENQ:
/* The camera has not yet given up. */
continue;
case ACK:
/* ACK received. We can proceed. */
return (GP_OK);
default:
/* This should not happen. */
return (GP_ERROR_CORRUPTED_DATA);
}
break;
}
break;
default:
/*
* The camera seems to send us data. We'll
* simply ignore it and try again (but make
* sure that we don't loop forever).
*/
CHECK (gp_port_flush (p, 0));
CHECK (gp_port_flush (p, 1));
if (level > 50)
return (GP_ERROR_CORRUPTED_DATA);
else
return (l_ping_rec (p, level + 1));
}
return (GP_OK);
}
int
l_ping (GPPort *p, GPFsErr *c)
{
return (l_ping_rec (p, 0));
}
