AP_HAL_ChibiOS: reset DMA after exiting soft serial

only configure DMA on groups that are actually being used for soft serial

Author: andyp1per

libraries/AP_HAL_ChibiOS/RCOutput.cpp

@@ -1788,6 +1788,7 @@ void RCOutput::send_pulses_DMAR(pwm_group &group, uint32_t buffer_length)
 #ifdef HAL_GPIO_LINE_GPIO54
     TOGGLE_PIN_DEBUG(54);
 #endif
+
 #if STM32_DMA_SUPPORTS_DMAMUX
     dmaSetRequestSource(group.dma, group.dma_up_channel);
 #endif
@@ -1914,6 +1915,11 @@ void RCOutput::dma_cancel(pwm_group& group)
 
   While serial output is active normal output to the channel group is
   suspended.
+
+  chanmask could refer to more than one group so it is assumed that
+  this function is always called before outputting to the group
+  implied by chan, but that DMA channels are setup only once
+  until serial_end() has been called
 */
 #if HAL_SERIAL_ESC_COMM_ENABLED
 bool RCOutput::serial_setup_output(uint8_t chan, uint32_t baudrate, uint32_t chanmask)
@@ -1923,7 +1929,7 @@ bool RCOutput::serial_setup_output(uint8_t chan, uint32_t baudrate, uint32_t cha
     chanmask >>= chan_offset;
     pwm_group *new_serial_group = nullptr;
 
-    // find the channel group
+    // find the channel group for the next output
     for (auto &group : pwm_group_list) {
         if (group.current_mode == MODE_PWM_BRUSHED) {
             // can't do serial output with brushed motors
@@ -1940,6 +1946,7 @@ bool RCOutput::serial_setup_output(uint8_t chan, uint32_t baudrate, uint32_t cha
         }
     }
 
+    // couldn't find a group, shutdown everything
     if (!new_serial_group) {
         if (in_soft_serial()) {
             // shutdown old group
@@ -1951,22 +1958,23 @@ bool RCOutput::serial_setup_output(uint8_t chan, uint32_t baudrate, uint32_t cha
     // stop further dshot output before we reconfigure the DMA
     serial_group = new_serial_group;
 
-    // setup the groups for serial output. We ask for a bit width of 1, which gets modified by the
+    // setup the unconfigured groups for serial output. We ask for a bit width of 1, which gets modified by the
     // we setup all groups so they all are setup with the right polarity, and to make switching between
     // channels in blheli pass-thru fast
     for (auto &group : pwm_group_list) {
-        if (group.ch_mask & chanmask) {
+        if ((group.ch_mask & chanmask) && !(group.ch_mask & serial_chanmask)) {
             if (!setup_group_DMA(group, baudrate, 10, false, DSHOT_BUFFER_LENGTH, 10, false)) {
                 serial_end();
                 return false;
             }
         }
     }
-
     // run the thread doing serial IO at highest priority. This is needed to ensure we don't
     // lose bytes when we switch between output and input
     serial_thread = chThdGetSelfX();
     serial_priority  = chThdGetSelfX()->realprio;
+    // mask of channels currently configured
+    serial_chanmask |= chanmask;
     chThdSetPriority(HIGHPRIO);
 
     // remember the bit period for serial_read_byte()
@@ -2002,7 +2010,6 @@ void RCOutput::fill_DMA_buffer_byte(dmar_uint_t *buffer, uint8_t stride, uint8_t
     }
 }
 
-
 /*
   send one serial byte, blocking call, should be called with the DMA lock held
 */
@@ -2229,11 +2236,15 @@ void RCOutput::serial_end(void)
         irq.waiter = nullptr;
         for (uint8_t i = 0; i < NUM_GROUPS; i++ ) {
             pwm_group &group = pwm_group_list[i];
-            set_group_mode(group);
-            set_freq_group(group);
+            // re-configure groups that were previous configured
+            if (group.ch_mask & serial_chanmask) {
+                dma_cancel(group);  // this ensures the DMA is in a sane state
+                set_group_mode(group);
+            }
         }
     }
     serial_group = nullptr;
+    serial_chanmask = 0;
 }
 #endif // HAL_SERIAL_ESC_COMM_ENABLED
 

libraries/AP_HAL_ChibiOS/RCOutput.h

@@ -512,6 +512,8 @@ class ChibiOS::RCOutput : public AP_HAL::RCOutput
     struct pwm_group *serial_group;
     thread_t *serial_thread;
     tprio_t serial_priority;
+    // mask of channels configured for serial output
+    uint32_t serial_chanmask;
 #endif // HAL_SERIAL_ESC_COMM_ENABLED
 
     static bool soft_serial_waiting() {