Increase RPi Pico PWM range and resolution to the max supported by HW

targets/TARGET_RASPBERRYPI/TARGET_RP2040/analogin_api.c

@@ -22,9 +22,8 @@
 #include "pinmap.h"
 #include "PeripheralPins.h"
 
-static float    const ADC_VREF_VOLTAGE     = 3.3f; /* 3.3V */
 static uint16_t const ADC_RESOLUTION_BITS   = 12;
-static float    const ADC_CONVERSION_FACTOR = ADC_VREF_VOLTAGE / (1 << 16);
+static float    const ADC_CONVERSION_FACTOR = 1.0f / (1 << 16);
 
 void analogin_init(analogin_t *obj, PinName pin)
 {

targets/TARGET_RASPBERRYPI/TARGET_RP2040/objects.h

@@ -114,12 +114,31 @@ struct spi_s {
     spi_inst_t * dev;
 };
 
-struct pwmout_s {
+struct pwmout_s
+{
+    /// Pin that the PWM is being sent out on
     PinName pin;
+
+    /// Slice number of this PWM (0-7).  Each slice contains two channels.
+    /// Each slice must have the same period but can have an independent duty cycle.
     uint8_t slice;
+
+    /// Channel of this PWM output on the slice (0 or 1)
     uint8_t channel;
-    uint16_t period;
+
+    /// Value after which this PWM channel will reset to 0.  This plus the clock divider controls the PWM period.
+    uint16_t top_count;
+
+    /// Current clock divider value that the channel is set to (hardware accepts 1-255.9375)
+    float clock_divider;
+
+    /// Current duty cycle percent
     float percent;
+
+    /// Current period setting in floating point seconds
+    float period;
+
+    /// Pico HAL config structure
     pwm_config cfg;
 };
 

targets/TARGET_RASPBERRYPI/TARGET_RP2040/pwmout_api.c

@@ -1,41 +1,21 @@
-/*
- * Copyright (c) 2018 Nordic Semiconductor ASA
- * All rights reserved.
+/* mbed Microcontroller Library
+ * Copyright (c) 2024, Arm Limited and affiliates.
+ * SPDX-License-Identifier: Apache-2.0
  *
- * Redistribution and use in source and binary forms, with or without modification,
- * are permitted provided that the following conditions are met:
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
  *
- *   1. Redistributions of source code must retain the above copyright notice, this list
- *      of conditions and the following disclaimer.
- *
- *   2. Redistributions in binary form, except as embedded into a Nordic Semiconductor ASA
- *      integrated circuit in a product or a software update for such product, must reproduce
- *      the above copyright notice, this list of conditions and the following disclaimer in
- *      the documentation and/or other materials provided with the distribution.
- *
- *   3. Neither the name of Nordic Semiconductor ASA nor the names of its contributors may be
- *      used to endorse or promote products derived from this software without specific prior
- *      written permission.
- *
- *   4. This software, with or without modification, must only be used with a
- *      Nordic Semiconductor ASA integrated circuit.
- *
- *   5. Any software provided in binary or object form under this license must not be reverse
- *      engineered, decompiled, modified and/or disassembled.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
- * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
- * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
- * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
- * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
- * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
- * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
- * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
- * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *     http://www.apache.org/licenses/LICENSE-2.0
  *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
  */
 
+
 #if DEVICE_PWMOUT
 
 #include "hal/pwmout_api.h"
@@ -45,7 +25,77 @@
 #include "hardware/clocks.h"
 #include "mbed_assert.h"
 
-const uint count_top = 1000;
+#include <math.h>
+
+// Change to 1 to enable debug prints of what's being calculated.
+// Must comment out the critical section calls in PwmOut to use.
+#define RP2040_PWMOUT_DEBUG 0
+
+#if RP2040_PWMOUT_DEBUG
+#include <stdio.h>
+#include <inttypes.h>
+#endif
+
+/// Largest top count value supported by hardware.  Using this value will provide the highest duty cycle resolution,
+/// but will limit the period to a maximum of (1 / (125 MHz / (65534 + 1)) =) 524 us
+const uint16_t MAX_TOP_COUNT = 65534;
+
+/// Value for PWM_CHn_DIV register that produces a division of 1
+const uint16_t PWM_CHn_DIV_1 = 0x010;
+
+/// Calculate the effective PWM period (in floating point seconds) based on a divider and top_count value
+static float calc_effective_pwm_period(float divider, uint16_t top_count)
+{
+    // Note: The hardware counts to top_count *inclusively*, so we have to add 1
+    // to get the number of clock cycles that a given top_count value will produce
+    return 1.0f / ((clock_get_hz(clk_sys) / divider) / (top_count + 1));
+}
+
+/// Calculate the best possible top_count value (rounding up) for a divider and a desired pwm period
+static uint16_t calc_top_count_for_period(float divider, float desired_pwm_period)
+{
+    // Derivation:
+    // desired_pwm_period = 1.0f / ((clock_get_hz(clk_sys) / divider) / (top_count + 1))
+    // desired_pwm_period = (top_count + 1) / (clock_get_hz(clk_sys) / divider)
+    // desired_pwm_period * (clock_get_hz(clk_sys) / divider) - 1 = top_count
+
+    long top_count_float = lroundf(desired_pwm_period * (clock_get_hz(clk_sys) / divider) - 1);
+    MBED_ASSERT(top_count_float <= MAX_TOP_COUNT);
+    return (uint16_t)top_count_float;
+}
+
+/// Calculate the best possible floating point divider value for a desired pwm period.
+/// This function assumes that top_count is set to MAX_TOP_COUNT.
+static float calc_divider_for_period(float desired_pwm_period)
+{
+    // Derivation:
+    // (desired_pwm_period * clock_get_hz(clk_sys)) / divider - 1 = top_count
+    // (desired_pwm_period * clock_get_hz(clk_sys)) / divider = top_count + 1
+    // divider = (desired_pwm_period * clock_get_hz(clk_sys)) / (top_count + 1)
+
+    return (desired_pwm_period * clock_get_hz(clk_sys)) / (MAX_TOP_COUNT + 1);
+}
+
+/// Convert PWM divider from floating point to a fixed point number (rounding up).
+/// The divider is returned as an 8.4 bit fixed point number, which is what the Pico registers use.
+static uint16_t pwm_divider_float_to_fixed(float divider_float)
+{
+    // To convert to a fixed point number, multiply by 16 and then round up
+    uint16_t divider_exact = ceil(divider_float * 16);
+
+    // Largest supported divider is 255 and 15/16
+    if(divider_exact > 0xFFF)
+    {
+        divider_exact = 0xFFF;
+    }
+    return divider_exact;
+}
+
+/// Convert PWM divider from the fixed point hardware value (8.4 bits) to a float.
+static float pwm_divider_fixed_to_float(uint16_t divider_fixed)
+{
+    return divider_fixed / 16.0f;
+}
 
 /** Initialize the pwm out peripheral and configure the pin
  *
@@ -60,11 +110,10 @@ void pwmout_init(pwmout_t *obj, PinName pin)
     obj->slice = pwm_gpio_to_slice_num(pin);
     obj->channel = pwm_gpio_to_channel(pin);
     obj->pin = pin;
-    obj->period = 0;
+    obj->top_count = MAX_TOP_COUNT;
     obj->percent = 0.5f;
-
     obj->cfg = pwm_get_default_config();
-    pwm_config_set_wrap(&(obj->cfg), count_top);
+    pwm_config_set_wrap(&(obj->cfg), obj->top_count);
 
     pwm_init(obj->slice, &(obj->cfg), false);
     gpio_set_function(pin, GPIO_FUNC_PWM);
@@ -89,7 +138,25 @@ void pwmout_free(pwmout_t *obj)
 void pwmout_write(pwmout_t *obj, float percent)
 {
     obj->percent = percent;
-    pwm_set_gpio_level(obj->pin, percent * (count_top + 1));
+
+    // Per datasheet section 4.5.2.2, a period value of top_count + 1 produces 100% duty cycle
+    int32_t new_reset_counts = lroundf((obj->top_count + 1) * percent);
+
+    // Clamp to valid values
+    if(new_reset_counts > obj->top_count + 1)
+    {
+        new_reset_counts = obj->top_count + 1;
+    }
+    else if(new_reset_counts < 0)
+    {
+        new_reset_counts = 0;
+    }
+
+#if RP2040_PWMOUT_DEBUG
+    printf("new_reset_counts: %" PRIu32 "\n", new_reset_counts);
+#endif
+
+    pwm_set_chan_level(obj->slice, obj->channel, new_reset_counts);
     pwm_set_enabled(obj->slice, true);
 }
 
@@ -114,8 +181,61 @@ float pwmout_read(pwmout_t *obj)
  */
 void pwmout_period(pwmout_t *obj, float period)
 {
-    /* Set new period. */
-    pwmout_period_us(obj, period * 1000000);
+    // Two possibilities here:
+    // - If the period is relatively short (< about 524 us), we want to keep the clock divider at 1
+    //    and reduce top_count to match the period
+    // - If the period is larger than what we can achieve with a clock divider of 1, we need to
+    //    use a higher clock divider, then recalculate the top_count to match
+
+    // Note: For math this complex, I wasn't able to avoid using floating point values.
+    // This function won't be too efficient, but for now I just want something that works and
+    // can access the full PWM range.
+
+    if(period <= calc_effective_pwm_period(1, MAX_TOP_COUNT))
+    {
+        // Short period.  Leave divider at 1 and reduce top_count to match the expected period
+        obj->clock_divider = 1.0f;
+        obj->cfg.div = PWM_CHn_DIV_1;
+        obj->top_count = calc_top_count_for_period(obj->clock_divider, period);
+    }
+    else
+    {
+        // Long period, need to use divider.
+
+        // Step 1: Calculate exact desired divider such that top_count would equal MAX_TOP_COUNT
+        float desired_divider = calc_divider_for_period(period);
+
+        // Step 2: Round desired divider upwards to the next value the hardware can do.
+        // We go upwards so that the top_count value can be trimmed downwards for the best period accuracy.
+        uint16_t divider_fixed_point = pwm_divider_float_to_fixed(desired_divider);
+        obj->cfg.div = divider_fixed_point;
+
+        // Step 3: Get the divider we'll actually be using as a float
+        obj->clock_divider = pwm_divider_fixed_to_float(divider_fixed_point);
+
+        // Step 4: For best accuracy, recalculate the top_count value using the divider.
+        obj->top_count = calc_top_count_for_period(obj->clock_divider, period);
+
+#if RP2040_PWMOUT_DEBUG
+        printf("period = %f, desired_divider = %f\n",
+               period,
+               desired_divider);
+#endif
+    }
+
+    // Save period for later
+    obj->period = period;
+
+#if RP2040_PWMOUT_DEBUG
+    printf("obj->clock_divider = %f, obj->cfg.div = %" PRIu32 ", obj->top_count = %" PRIu16 "\n",
+           obj->clock_divider,
+           obj->cfg.div,
+           obj->top_count);
+#endif
+
+    // Set the new divider and top_count values.
+    pwm_config_set_wrap(&(obj->cfg), obj->top_count);
+    pwm_init(obj->slice, &(obj->cfg), false);
 }
 
 /** Set the PWM period specified in miliseconds, keeping the duty cycle the same
@@ -126,7 +246,7 @@ void pwmout_period(pwmout_t *obj, float period)
 void pwmout_period_ms(pwmout_t *obj, int period)
 {
     /* Set new period. */
-    pwmout_period_us(obj, period * 1000);
+    pwmout_period(obj, period / 1000.0f);
 }
 
 /** Set the PWM period specified in microseconds, keeping the duty cycle the same
@@ -136,18 +256,18 @@ void pwmout_period_ms(pwmout_t *obj, int period)
  */
 void pwmout_period_us(pwmout_t *obj, int period)
 {
-    obj->period = period;
-
-    // min_period should be 8us
-    uint32_t min_period = 1000000 * count_top / clock_get_hz(clk_sys);
-
-    pwm_config_set_clkdiv(&(obj->cfg), (float)period / (float)min_period);
-    pwm_init(obj->slice, &(obj->cfg), false);
+    /* Set new period. */
+    pwmout_period(obj, period / 1000000.0f);
 }
 
+/** Read the PWM period specified in microseconds
+ *
+ * @param obj The pwmout object
+ * @return A int output period
+ */
 int pwmout_read_period_us(pwmout_t *obj)
 {
-    return obj->period;
+    return lroundf(1000000 * calc_effective_pwm_period(obj->clock_divider, obj->top_count));
 }
 
 /** Set the PWM pulsewidth specified in seconds, keeping the period the same.
@@ -157,7 +277,7 @@ int pwmout_read_period_us(pwmout_t *obj)
  */
 void pwmout_pulsewidth(pwmout_t *obj, float pulse)
 {
-    pwmout_pulsewidth_us(obj, pulse * 1000000);
+    pwmout_write(obj, pulse / obj->period);
 }
 
 /** Set the PWM pulsewidth specified in miliseconds, keeping the period the same.
@@ -167,7 +287,7 @@ void pwmout_pulsewidth(pwmout_t *obj, float pulse)
  */
 void pwmout_pulsewidth_ms(pwmout_t *obj, int pulse)
 {
-    pwmout_pulsewidth_us(obj, pulse * 1000);
+    pwmout_write(obj, (pulse * .001f) / obj->period);
 }
 
 /** Set the PWM pulsewidth specified in microseconds, keeping the period the same.
@@ -177,19 +297,11 @@ void pwmout_pulsewidth_ms(pwmout_t *obj, int pulse)
  */
 void pwmout_pulsewidth_us(pwmout_t *obj, int pulse)
 {
-    /* Cap pulsewidth to period. */
-    if (pulse > obj->period) {
-        pulse = obj->period;
-    }
-
-    obj->percent = (float) pulse / (float) obj->period;
-
-    /* Restart instance with new values. */
-    pwmout_write(obj, obj->percent);
+    pwmout_write(obj, (pulse * .000001f) / obj->period);
 }
 
 int pwmout_read_pulsewidth_us(pwmout_t *obj) {
-    return (obj->period) * (obj->percent);
+    return lroundf(obj->period * obj->percent * 1000000);
 }
 
 const PinMap *pwmout_pinmap()