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nimble/ll: Add fast path for aux chain scheduling

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For short aux offsets we can to usecs to ticks conversion using only
32-bit arithmetics without integer division. This is much faster than
generic routine, especially on M0 (e.g. CMAC) which does not have hw
support for integer division. The faster calculation is even more
accurate than generic one since it's never off by 1 tick.

This is a temporary solution until we have more generic timer routines
that do the same kind of optimizations.
This commit is contained in:
Andrzej Kaczmarek
2021-11-04 11:35:49 +01:00
parent 7f63bd094e
commit ed4563741c
1 changed files with 20 additions and 4 deletions
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nimble/controller/src/ble_ll_sched.c
+20 -4
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@@ -786,6 +786,22 @@ ble_ll_sched_slave_new(struct ble_ll_conn_sm *connsm)
return rc;
}
#if MYNEWT_VAL(BLE_LL_CFG_FEAT_LL_EXT_ADV)
static inline uint32_t
usecs_to_ticks_fast(uint32_t usecs)
{
uint32_t ticks;
if (usecs <= 31249) {
ticks = (usecs * 137439) / 4194304;
} else {
ticks = os_cputime_usecs_to_ticks(usecs);
}
return ticks;
}
#endif
#if MYNEWT_VAL(BLE_LL_CFG_FEAT_LL_PERIODIC_ADV)
/*
* Determines if the schedule item overlaps the currently running schedule
@@ -887,7 +903,7 @@ ble_ll_sched_sync(struct ble_ll_sched_item *sch,
os_sr_t sr;
int rc = 0;
off_ticks = os_cputime_usecs_to_ticks(offset);
off_ticks = usecs_to_ticks_fast(offset);
off_rem_usecs = offset - os_cputime_ticks_to_usecs(off_ticks);
start_time = beg_cputime + off_ticks;
@@ -899,7 +915,7 @@ ble_ll_sched_sync(struct ble_ll_sched_item *sch,
dur = ble_ll_pdu_tx_time_get(MYNEWT_VAL(BLE_LL_SCHED_SCAN_SYNC_PDU_LEN),
phy_mode);
end_time = start_time + os_cputime_usecs_to_ticks(dur);
end_time = start_time + usecs_to_ticks_fast(dur);
start_time -= g_ble_ll_sched_offset_ticks;
@@ -1257,12 +1273,12 @@ ble_ll_sched_scan_aux(struct ble_ll_sched_item *sch, uint32_t pdu_time,
int rc;
offset_us += pdu_time_rem;
offset_ticks = os_cputime_usecs_to_ticks(offset_us);
offset_ticks = usecs_to_ticks_fast(offset_us);
sch->start_time = pdu_time + offset_ticks - g_ble_ll_sched_offset_ticks;
sch->remainder = offset_us - os_cputime_ticks_to_usecs(offset_ticks);
/* TODO: make some sane slot reservation */
sch->end_time = sch->start_time + os_cputime_usecs_to_ticks(5000);
sch->end_time = sch->start_time + usecs_to_ticks_fast(5000);
OS_ENTER_CRITICAL(sr);