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trxcon/scheduler: substitute lost TDMA frames on Downlink 

It may happen that one or more Downlink bursts are lost on their
way to the MS due to a variety of reasons. Modern transceivers
supporting TRXDv1 protocol would substitute lost bursts with
so-called NOPE indications. Hovewer, neither fake_trx.py nor
grgsm_trx do support this feature at the moment.

We can still detect and compensate TDMA frame loss per logical
channels in the same way as it's already done in osmo-bts-trx.
In short, we should keep TDMA frame number of the last received
burst in the logical channel state, and using the appropriate
multiframe layout, check if there were any gaps between TDMA
frame number of the current burst and the stored one.

Change-Id: I3551d79796a3730565c2c70577e9d134e636f275
This commit is contained in:
Vadim Yanitskiy 2020-03-04 21:22:11 +07:00 committed by laforge
parent 8c760f8f05
commit 431dcd00f0
2 changed files with 100 additions and 55 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

141
src/host/trxcon/sched_trx.c
View File

@ -321,9 +321,6 @@ int sched_trx_reset_ts(struct trx_instance *trx, int tn)
if (ts == NULL)
return -EINVAL;
/* Flush TS frame counter */
ts->mf_last_fn = 0;
/* Undefine multiframe layout */
ts->mf_layout = NULL;
@ -491,6 +488,9 @@ static void sched_trx_reset_lchan(struct trx_lchan_state *lchan)
/* Reset ciphering state */
memset(&lchan->a5, 0x00, sizeof(lchan->a5));
/* Reset TDMA frame statistics */
memset(&lchan->tdma, 0x00, sizeof(lchan->tdma));
}
int sched_trx_deactivate_lchan(struct trx_ts *ts, enum trx_lchan_type chan)
@ -610,8 +610,65 @@ static void sched_trx_a5_burst_enc(struct trx_lchan_state *lchan,
}
}
static int subst_frame_loss(struct trx_lchan_state *lchan,
trx_lchan_rx_func *handler,
uint32_t fn)
{
const struct trx_multiframe *mf;
const struct trx_frame *fp;
unsigned int elapsed, i;
/* Wait until at least one TDMA frame is processed */
if (lchan->tdma.num_proc == 0)
return -EAGAIN;
/* Short alias for the current multiframe */
mf = lchan->ts->mf_layout;
/* How many frames elapsed since the last one? */
elapsed = TDMA_FN_SUB(fn, lchan->tdma.last_proc);
if (elapsed > mf->period) {
LOGP(DSCHD, LOGL_NOTICE, "Too many (>%u) contiguous TDMA frames elapsed (%u) "
"since the last processed fn=%u\n", mf->period,
elapsed, lchan->tdma.last_proc);
} else if (elapsed == 0) {
LOGP(DSCHD, LOGL_ERROR, "No TDMA frames elapsed since the last processed "
"fn=%u, must be a bug?\n", lchan->tdma.last_proc);
return -EIO;
}
/* TODO: make bits constant */
static sbit_t bits[148] = { 0 };
struct trx_meas_set fake_meas = {
.fn = lchan->tdma.last_proc,
.rssi = -120,
.toa256 = 0,
};
/* Traverse from fp till the current frame */
for (i = 0; i < elapsed - 1; i++) {
fp = &mf->frames[TDMA_FN_INC(&fake_meas.fn) % mf->period];
if (fp->dl_chan != lchan->type)
continue;
LOGP(DSCHD, LOGL_NOTICE, "Substituting lost TDMA frame %u on %s\n",
fake_meas.fn, trx_lchan_desc[lchan->type].name);
handler(lchan->ts->trx, lchan->ts, lchan,
fake_meas.fn, fp->dl_bid,
bits, &fake_meas);
/* Update TDMA frame statistics */
lchan->tdma.last_proc = fake_meas.fn;
lchan->tdma.num_proc++;
lchan->tdma.num_lost++;
}
return 0;
}
int sched_trx_handle_rx_burst(struct trx_instance *trx, uint8_t tn,
uint32_t burst_fn, sbit_t *bits, uint16_t nbits,
uint32_t fn, sbit_t *bits, uint16_t nbits,
const struct trx_meas_set *meas)
{
struct trx_lchan_state *lchan;
@ -620,7 +677,6 @@ int sched_trx_handle_rx_burst(struct trx_instance *trx, uint8_t tn,
trx_lchan_rx_func *handler;
enum trx_lchan_type chan;
uint32_t fn, elapsed;
uint8_t offset, bid;
/* Check whether required timeslot is allocated and configured */
@ -631,61 +687,42 @@ int sched_trx_handle_rx_burst(struct trx_instance *trx, uint8_t tn,
return -EINVAL;
}
/* Calculate how many frames have been elapsed */
elapsed = TDMA_FN_SUB(burst_fn, ts->mf_last_fn);
/* Get frame from multiframe */
offset = fn % ts->mf_layout->period;
frame = ts->mf_layout->frames + offset;
/**
* If not too many frames have been elapsed,
* start counting from last fn + 1
*/
if (elapsed < 10)
fn = TDMA_FN_SUM(ts->mf_last_fn, 1);
else
fn = burst_fn;
/* Get required info from frame */
bid = frame->dl_bid;
chan = frame->dl_chan;
handler = trx_lchan_desc[chan].rx_fn;
while (1) {
/* Get frame from multiframe */
offset = fn % ts->mf_layout->period;
frame = ts->mf_layout->frames + offset;
/* Omit bursts which have no handler, like IDLE bursts.
* TODO: handle noise indications during IDLE frames. */
if (!handler)
return -ENODEV;
/* Get required info from frame */
bid = frame->dl_bid;
chan = frame->dl_chan;
handler = trx_lchan_desc[chan].rx_fn;
/* Find required channel state */
lchan = sched_trx_find_lchan(ts, chan);
if (lchan == NULL)
return -ENODEV;
/* Omit bursts which have no handler, like IDLE bursts */
if (!handler)
goto next_frame;
/* Ensure that channel is active */
if (!lchan->active)
return 0;
/* Find required channel state */
lchan = sched_trx_find_lchan(ts, chan);
if (lchan == NULL)
goto next_frame;
/* Compensate lost TDMA frames (if any) */
subst_frame_loss(lchan, handler, fn);
/* Ensure that channel is active */
if (!lchan->active)
goto next_frame;
/* Perform A5/X decryption if required */
if (lchan->a5.algo)
sched_trx_a5_burst_dec(lchan, fn, bits);
/* Reached current fn */
if (fn == burst_fn) {
/* Perform A5/X decryption if required */
if (lchan->a5.algo)
sched_trx_a5_burst_dec(lchan, fn, bits);
/* Put burst to handler */
handler(trx, ts, lchan, fn, bid, bits, meas);
/* Put burst to handler */
handler(trx, ts, lchan, fn, bid, bits, meas);
}
next_frame:
/* Reached current fn */
if (fn == burst_fn)
break;
TDMA_FN_INC(&fn);
}
/* Set last processed frame number */
ts->mf_last_fn = fn;
/* Update TDMA frame statistics */
lchan->tdma.last_proc = fn;
lchan->tdma.num_proc++;
return 0;
}

14
src/host/trxcon/sched_trx.h
View File

@ -209,6 +209,16 @@ struct trx_lchan_state {
/*! \brief AVG measurements of the last received block */
struct trx_meas_set meas_avg;
/*! \brief TDMA loss detection state */
struct {
/*! \brief Last processed TDMA frame number */
uint32_t last_proc;
/*! \brief Number of processed TDMA frames */
unsigned long num_proc;
/*! \brief Number of lost TDMA frames */
unsigned long num_lost;
} tdma;
/*! \brief SACCH state */
struct {
/*! \brief Cached measurement report (last received) */
@ -255,8 +265,6 @@ struct trx_lchan_state {
struct trx_ts {
/*! \brief Timeslot index within a frame (0..7) */
uint8_t index;
/*! \brief Last received frame number */
uint32_t mf_last_fn;
/*! \brief Pointer to multiframe layout */
const struct trx_multiframe *mf_layout;
@ -356,7 +364,7 @@ void sched_prim_drop(struct trx_lchan_state *lchan);
void sched_prim_flush_queue(struct llist_head *list);
int sched_trx_handle_rx_burst(struct trx_instance *trx, uint8_t tn,
uint32_t burst_fn, sbit_t *bits, uint16_t nbits,
uint32_t fn, sbit_t *bits, uint16_t nbits,
const struct trx_meas_set *meas);
int sched_trx_handle_tx_burst(struct trx_instance *trx,
struct trx_ts *ts, struct trx_lchan_state *lchan,