AP_HAL_ChibiOS: fix dshot timeout bug where the elapsed pulse is longer than the send time

dshot timeouts should be no longer than the pulse interval
use correct timestamp for dmar send time

libraries/AP_HAL_ChibiOS/RCOutput.cpp

@@ -255,17 +255,18 @@ void RCOutput::dshot_collect_dma_locks(uint32_t time_out_us)
             const uint32_t pulse_elapsed_us = now - group.last_dmar_send_us;
             uint32_t wait_us = 0;
             if (now < time_out_us) {
-                wait_us = MAX(time_out_us - now, group.dshot_pulse_send_time_us - pulse_elapsed_us);
-            } else if (pulse_elapsed_us < group.dshot_pulse_send_time_us) {
+                wait_us = time_out_us - now;
+            }
+            if (pulse_elapsed_us < group.dshot_pulse_send_time_us) {
                 // better to let the burst write in progress complete rather than cancelling mid way through
-                wait_us = group.dshot_pulse_send_time_us - pulse_elapsed_us;
+                wait_us = MAX(wait_us, group.dshot_pulse_send_time_us - pulse_elapsed_us);
             }
 
             // waiting for a very short period of time can cause a
             // timer wrap with ChibiOS timers. Use CH_CFG_ST_TIMEDELTA
-            // as minimum. Don't allow for a very long delay (over 1200us)
+            // as minimum. Don't allow for a very long delay (over _dshot_period_us)
             // to prevent bugs in handling timer wrap
-            const uint32_t max_delay_us = 1200;
+            const uint32_t max_delay_us = _dshot_period_us;
             const uint32_t min_delay_us = 10; // matches our CH_CFG_ST_TIMEDELTA
             wait_us = constrain_uint32(wait_us, min_delay_us, max_delay_us);
             mask = chEvtWaitOneTimeout(group.dshot_event_mask, chTimeUS2I(wait_us));
@@ -1566,7 +1567,7 @@ void RCOutput::send_pulses_DMAR(pwm_group &group, uint32_t buffer_length)
 
     dmaStreamEnable(group.dma);
     // record when the transaction was started
-    group.last_dmar_send_us = AP_HAL::micros64();
+    group.last_dmar_send_us = AP_HAL::micros();
 #endif //#ifndef DISABLE_DSHOT
 }