Improved servocluster teardown

drivers/pwm/pwm_cluster.cpp

@@ -150,9 +150,22 @@ PWMCluster::~PWMCluster() {
   if(initialised) {
     pio_sm_set_enabled(pio, sm, false);
 
-    dma_channel_abort(dma_channel);
-    dma_channel_set_irq0_enabled(dma_channel, false);
-    //dma_channel_unclaim(dma_channel); // This does not seem to work
+    // Tear down the DMA channel.
+    // This is copied from: https://github.com/raspberrypi/pico-sdk/pull/744/commits/5e0e8004dd790f0155426e6689a66e08a83cd9fc
+    uint32_t irq0_save = dma_hw->inte0 & (1u << dma_channel);
+    hw_clear_bits(&dma_hw->inte0, irq0_save);
+
+    dma_hw->abort = 1u << dma_channel;
+
+    // To fence off on in-flight transfers, the BUSY bit should be polled
+    // rather than the ABORT bit, because the ABORT bit can clear prematurely.
+    while (dma_hw->ch[dma_channel].ctrl_trig & DMA_CH0_CTRL_TRIG_BUSY_BITS) tight_loop_contents();
+
+    // Clear the interrupt (if any) and restore the interrupt masks.
+    dma_hw->ints0 = 1u << dma_channel;
+    hw_set_bits(&dma_hw->inte0, irq0_save);
+
+    dma_channel_unclaim(dma_channel); // This works now the teardown behaves correctly
     clusters[dma_channel] = nullptr;
 
     pio_sm_unclaim(pio, sm);

micropython/examples/servo2040/current_meter.py

@@ -1,3 +1,4 @@
+import gc
 import time
 from machine import Pin
 from pimoroni import Analog, AnalogMux, Button
@@ -21,6 +22,9 @@ MAX_CURRENT = 3.0     # The maximum current, in amps, to show on the meter
 SAMPLES = 50          # The number of current measurements to take per reading
 TIME_BETWEEN = 0.001  # The time between each current measurement
 
+# Free up hardware resources ahead of creating a new ServoCluster
+gc.collect()
+
 # Create the user button
 user_sw = Button(servo2040.USER_SW)
 

micropython/examples/servo2040/servo_cluster.py

@@ -1,3 +1,4 @@
+import gc
 import time
 import math
 from servo import ServoCluster, servo2040
@@ -10,6 +11,9 @@ such may have problems when running code multiple times.
 If you encounter issues, try resetting your board.
 """
 
+# Free up hardware resources ahead of creating a new ServoCluster
+gc.collect()
+
 # Create a servo cluster for pins 0 to 3, using PIO 0 and State Machine 0
 START_PIN = servo2040.SERVO_1
 END_PIN = servo2040.SERVO_4

micropython/examples/servo2040/servo_wave.py

@@ -1,3 +1,4 @@
+import gc
 import time
 import math
 from pimoroni import Button
@@ -19,6 +20,9 @@ BRIGHTNESS = 0.4      # The brightness of the LEDs
 UPDATES = 50          # How many times to update LEDs and Servos per second
 SERVO_EXTENT = 80.0   # How far from zero to move the servos
 
+# Free up hardware resources ahead of creating a new ServoCluster
+gc.collect()
+
 # Create a servo cluster for pins 0 to 7, using PIO 0 and State Machine 0
 START_PIN = servo2040.SERVO_1
 END_PIN = servo2040.SERVO_8

micropython/modules/servo/servo.cpp

@@ -1365,7 +1365,7 @@ mp_obj_t ServoCluster_make_new(const mp_obj_type_t *type, size_t n_args, size_t
         delete cluster;
         m_del(PWMCluster::Sequence, seq_buffer, PWMCluster::NUM_BUFFERS * 2);
         m_del(PWMCluster::TransitionData, dat_buffer, PWMCluster::BUFFER_SIZE * 2);
-        mp_raise_msg(&mp_type_RuntimeError, "unable to allocate the hardware resources needed to initialise this ServoCluster");//. Try running `import gc` followed by `gc.collect()`, then create this ServoCluster");
+        mp_raise_msg(&mp_type_RuntimeError, "unable to allocate the hardware resources needed to initialise this ServoCluster. Try running `import gc` followed by `gc.collect()` before creating it");
     }
 
     self = m_new_obj_with_finaliser(_ServoCluster_obj_t);