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Don't accept all-zeros messages (e.g. off the network - the demodulator

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doesn't accept them already)
This commit is contained in:
Oliver Jowett 2016-09-14 16:11:31 +01:00
parent b827806ce8
commit 9e179d46bf
1 changed files with 5 additions and 1 deletions
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6
mode_s.c
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@ -307,12 +307,12 @@ static inline __attribute__((always_inline)) unsigned getbits(unsigned char *da
// -1: message might be valid, but we couldn't validate the CRC against a known ICAO // -1: message might be valid, but we couldn't validate the CRC against a known ICAO
// -2: bad message or unrepairable CRC error // -2: bad message or unrepairable CRC error
static unsigned char all_zeros[14] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
int scoreModesMessage(unsigned char *msg, int validbits) int scoreModesMessage(unsigned char *msg, int validbits)
{ {
int msgtype, msgbits, crc, iid; int msgtype, msgbits, crc, iid;
uint32_t addr; uint32_t addr;
struct errorinfo *ei; struct errorinfo *ei;
static unsigned char all_zeros[14] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
if (validbits < 56) if (validbits < 56)
return -2; return -2;
@ -434,6 +434,10 @@ int decodeModesMessage(struct modesMessage *mm, unsigned char *msg)
} }
msg = mm->msg; msg = mm->msg;
// don't accept all-zeros messages
if (!memcmp(all_zeros, msg, 7))
return -2;
// Get the message type ASAP as other operations depend on this // Get the message type ASAP as other operations depend on this
mm->msgtype = getbits(msg, 1, 5); // Downlink Format mm->msgtype = getbits(msg, 1, 5); // Downlink Format
mm->msgbits = modesMessageLenByType(mm->msgtype); mm->msgbits = modesMessageLenByType(mm->msgtype);