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Better error message for invalid channel which could 

be caused by use of SMACK rather than standard KISS.
This commit is contained in:
wb2osz 2019-04-21 19:17:06 -04:00
parent c559f0d443
commit aea1eb7b41
1 changed files with 13 additions and 18 deletions
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27
kiss_frame.c
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@ -539,8 +539,6 @@ void kiss_process_msg (unsigned char *kiss_msg, int kiss_len, int debug, int cli
kissnet_copy (kiss_msg, kiss_len, port, cmd, client);
}
/* Special hack - Discard apparently bad data from Linux AX25. */
/* Note July 2017: There is a variant of of KISS, called SMACK, that assumes */
/* a TNC can never have more than 8 ports. http://symek.de/g/smack.html */
/* It uses the MSB to indicate that a checksum is added. I wonder if this */
@ -580,27 +578,24 @@ void kiss_process_msg (unsigned char *kiss_msg, int kiss_len, int debug, int cli
// This workaround seems sound to me, though, so perhaps this is just a documentation issue.
if (kiss_len > 16 &&
(port == 2 || port == 8) &&
kiss_msg[1] == 'Q' << 1 &&
kiss_msg[2] == 'S' << 1 &&
kiss_msg[3] == 'T' << 1 &&
kiss_msg[4] == ' ' << 1 &&
kiss_msg[15] == 3 &&
kiss_msg[16] == 0xcd) {
// Would it make sense to implement SMACK? I don't think so.
// Adding a checksum to the KISS data offers no benefit because it is very reliable.
// It violates the original protocol specification which states that 16 ports (radio channels) are possible.
// SMACK imposes a limit of 8. That limit might have been OK back in 1991 but not now.
// There are people using more than 8 radio channels (using SDR not traditional radios) with direwolf.
if (debug) {
text_color_set(DW_COLOR_ERROR);
dw_printf ("Special case - Drop packets which appear to be in error.\n");
}
return;
}
/* Verify that the port (channel) number is valid. */
if (port < 0 || port >= MAX_CHANS || ! save_audio_config_p->achan[port].valid) {
text_color_set(DW_COLOR_ERROR);
dw_printf ("Invalid transmit channel %d from KISS client app.\n", port);
dw_printf ("\n");
dw_printf ("Are you using AX.25 for Linux? It might be trying to use a modified\n");
dw_printf ("version of KISS which uses the port field differently than the\n");
dw_printf ("original KISS protocol specification. The solution might be to use\n");
dw_printf ("a command like \"kissparms -c 1 -p radio\" to set CRC none mode.\n");
dw_printf ("\n");
text_color_set(DW_COLOR_DEBUG);
kiss_debug_print (FROM_CLIENT, NULL, kiss_msg, kiss_len);
return;