disallow duty cycle rounding to 0

Author: timchinowsky

ports/raspberrypi/common-hal/pwmio/PWMOut.c

@@ -176,6 +176,10 @@ extern void common_hal_pwmio_pwmout_set_duty_cycle(pwmio_pwmout_obj_t *self, uin
     } else {
         compare_count = ((uint32_t)duty * self->top + MAX_TOP / 2) / MAX_TOP;
     }
+    // do not allow count to be 0 (due to rounding) unless duty 0 was requested
+    if (compare_count == 0 && duty != 0) {
+        compare_count = 1;
+    }
     // compare_count is the CC register value, which should be TOP+1 for 100% duty cycle.
     pwm_set_chan_level(self->slice, self->ab_channel, compare_count);
 }

tests/circuitpython-manual/pwmio/code_extremes.py

@@ -0,0 +1,87 @@
+import board
+import pwmio
+import random
+import time
+import microcontroller
+import os
+import sys
+import random
+
+exponents = [
+    2,
+    3,
+    4,
+    5,
+    6,
+    7,
+]
+
+freqs = [int(10**f) for f in exponents]
+
+top = 65536
+den = 10
+duties = [32767, 65535, 1, 65534, 0, 0]
+freq_duration = 1.2
+duty_duration = 0.2
+
+print("\n\n")
+board_name = sys.implementation[2]
+
+pins = {
+    "Feather RP2040": (("D4", ""),),
+    "RP2040-Zero": (("GP15", ""),),
+    "Grand Central": (("D51", "TCC"), ("A15", "TC")),
+    "Metro M0": (("A2", "TC"), ("A3", "TCC")),
+    "ESP32-S3-DevKit": (("IO6", ""),),  # marked D5 on board for XIAO-ESP32-s3
+    "Feather ESP32-S2": (("D9", ""),),
+    "XIAO nRF52840": (("D9", ""),),
+}
+
+for board_key in pins:
+    if board_key in board_name:
+        pins_to_use = pins[board_key]
+        break
+
+while True:
+    for pin_name, pin_type in pins_to_use:
+        pin = getattr(board, pin_name)
+        print('title="', end="")
+        print(f"{board_name} at {microcontroller.cpu.frequency} Hz, pin {pin_name}", end="")
+        if len(pin_type) > 0:
+            print(f" ({pin_type})", end="")
+        print('",')
+        print(f'subtitle="{freq_duration:0.1f}s per frequency",')
+        print(f'version="{sys.version}",')
+        print("freq_calls=", end="")
+        pwm = pwmio.PWMOut(pin, variable_frequency=True)
+        t0 = time.monotonic()
+        duty_time = t0 + duty_duration
+        print("(", end="")
+        offset = 0
+        increment = 1
+        for freq in freqs:
+            i = 0
+            try:
+                pwm.frequency = freq
+            except ValueError:
+                break
+            freq_time = t0 + freq_duration
+            duty_time = t0 + duty_duration
+            j = 0
+            while time.monotonic() < freq_time:
+                duty = duties[j]
+                pwm.duty_cycle = duty
+                while time.monotonic() < duty_time and time.monotonic() < freq_time:
+                    pass
+                j += 1
+                j = min(j, len(duties) - 1)
+                duty_time += duty_duration
+                i += 1
+                if time.monotonic() > freq_time:
+                    break
+            t0 = freq_time
+            print(f"({freq}, {i/freq_duration:.0f}), ", end="")
+        print(")")
+        print("done.")
+        pwm.deinit()
+        time.sleep(5)