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Make sure sync header was fully received 

The sync header consists of 16 zero-bits followed by 1 one-bit. Before,
subchan_demux only tested for the 16 zero-bits. But if the previous
frame ended in one or more zero-bits these were then already counted as
belonging to the sync header, leading to a frame that was shifted by one
or more bits.
This commit is contained in:
Dieter Spaar 2012-10-08 21:36:03 +02:00 committed by Holger Hans Peter Freyther
parent d72c478b06
commit 08c103251c
1 changed files with 9 additions and 8 deletions
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17
src/subchan_demux.c
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@ -46,18 +46,18 @@ static inline void append_bit(struct demux_subch *sch, uint8_t bit)
#define SYNC_HDR_BITS 16
static const uint8_t nullbytes[SYNC_HDR_BITS];
/* check if we have just completed the 16 bit zero sync header,
* in accordance with GSM TS 08.60 Chapter 4.8.1 */
/* check if we have just completed the 16 bit zero + 1 bit one sync
* header, in accordance with GSM TS 08.60 Chapter 4.8.1 */
static int sync_hdr_complete(struct demux_subch *sch, uint8_t bit)
{
if (bit == 0)
sch->consecutive_zeros++;
else
else {
if (sch->consecutive_zeros >= SYNC_HDR_BITS) {
sch->consecutive_zeros = 0;
return 1;
}
sch->consecutive_zeros = 0;
if (sch->consecutive_zeros >= SYNC_HDR_BITS) {
sch->consecutive_zeros = 0;
return 1;
}
return 0;
@ -67,10 +67,11 @@ static int sync_hdr_complete(struct demux_subch *sch, uint8_t bit)
static void resync_to_here(struct demux_subch *sch)
{
memset(sch->out_bitbuf, 0, SYNC_HDR_BITS);
sch->out_bitbuf[SYNC_HDR_BITS] = 1;
/* set index in a way that we can continue receiving bits after
* the end of the SYNC header */
sch->out_idx = SYNC_HDR_BITS;
sch->out_idx = SYNC_HDR_BITS + 1;
sch->in_sync = 1;
}