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--- mp_pwm_led [2021/10/13 21:52]
gongyusu [卓晴老师的例子]
+++ mp_pwm_led [2023/08/01 09:54] (当前版本)
group003
@@ 行 1: / 行 1: @@
 ## 用PWM控制LED亮度
+### 1. RP2040的PWM
+脉宽调制(PWM)是一种数字信号提供平滑变化的平均电压的方案。这是通过一定宽度的正脉冲以一定的间隔实现的。高消耗时间的比例称为占空比。这可以用来近似模拟输出，或控制开关模式电力电子。
+RP2040 PWM模块有8个相同的切片。每个薄片可以驱动两个PWM输出信号，或测量一个输入信号的频率或占空比。这提供了总共多达16个可控PWM输出。所有30个GPIO引脚都可以由PWM模块驱动。
+{{ :rp2040_pwm.png |}}
+单个PWM片。一个16位计数器从0计数到一些编程值，然后wrap到零，或计数回来，取决于PWM模式。A和B输出过渡高和低基于当前计数值和预编程的A和B阈值。计数器根据若干事件前进:它可以是自由运行的，或者由B引脚上输入信号的电平或边缘门控。分数分频器降低了整体计数率，以更好地控制输出频率。
+ A single PWM slice. A 16-bit counter counts from 0 up to some programmed value, and then wraps to zero, or counts back down again, depending on PWM mode. The A and B outputs transition high and low based on the current count value and the preprogrammed A and B thresholds. The counter advances based on a number of events: it may be free- running, or gated by level or edge of an input signal on the B pin. A fractional divider slows the overall count rate for finer control of output frequency.
+每个PWM片配置如下:
+  * 16位计数器
+  * 8.4分数时钟分频器
+  * 两个独立的输出通道，占空比从0%到100%包含
+  * 用于频率测量的边缘敏感输入模式
+  * 用于占空比测量的电平敏感输入模式
+  * 可配置计数器warp值
+    * Wrap和水平寄存器是双缓冲，而PWM运行时，可以改变中断请求和DMA请求计数器Wrap以便没有竞争
+  * 相位可以在运行时精确地提前或延迟(增加一个计数)
+可以通过单个全局控件寄存器同时启用或禁用片。然后这些薄片完美地同步运行，这样就可以通过多个薄片的输出来切换更复杂的电源电路。
+{{ :rp2040_pwm_mach.png |}}
+{{ :rp2040_pwm_reg.png |}}
+### 2. 参考示例
 使用电位器的直流电压来控制LED的亮度，LED的亮度由PWM进行控制，这个任务在MicroPython中非常简单。
@@ 行 6: / 行 30: @@
 # led-pwm.py
-# POT - Pico GPIO 26 ADC0
+# POT - Pico GPIO 28 ADC2
-# RED LED - Pico GPIO 19
+# RED LED - Pico GPIO 25
 # EETree Info&Tech 2021
@@ 行 17: / 行 41: @@
 import utime
-led_red = machine.PWM(machine.Pin(19))
+led_red = machine.PWM(machine.Pin(25))
-potentiometer = machine.ADC(26)
+potentiometer = machine.ADC(28)
 led_red.freq(1000)
@@ 行 65: / 行 89: @@
 </code>
 PWM是软件PWM，它可以设置在任意管脚上。初步测试过Pin0, 15, 16等等。都具有相类似波形。
+### 3. 呼吸灯的例子
+<code python>
+from machine import Pin, PWM,Timer
+LED = PWM(Pin(25))
+n = 0
+def breathing(t):
+    global n
+    LED.duty_u16(abs(32000- n*1000))
+    n = (n + 1) % 64
+T0 = Timer(-1)
+T0.init(period=20, mode=Timer.PERIODIC, callback=breathing)
+</code>
 ### 3. Maker.io上的文章
 [[https://www.digikey.com/en/maker/projects/raspberry-pi-pico-and-rp2040-micropython-part-1-blink/58b3c31ac93649849b58824caa00529c|使用MicroPython点灯]]
+### 4. 使用DMA来传递PWM控制字
+<code c>
+/**
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+// Fade an LED between low and high brightness. An interrupt handler updates
+// the PWM slice's output level each time the counter wraps.
+#include "pico/stdlib.h"
+#include <stdio.h>
+#include "pico/time.h"
+#include "hardware/irq.h"
+#include "hardware/pwm.h"
+#ifdef PICO_DEFAULT_LED_PIN
+void on_pwm_wrap() {
+    static int fade = 0;
+    static bool going_up = true;
+    // Clear the interrupt flag that brought us here
+    pwm_clear_irq(pwm_gpio_to_slice_num(PICO_DEFAULT_LED_PIN));
+    if (going_up) {
+        ++fade;
+        if (fade > 255) {
+            fade = 255;
+            going_up = false;
+        }
+    } else {
+        --fade;
+        if (fade < 0) {
+            fade = 0;
+            going_up = true;
+        }
+    }
+    // Square the fade value to make the LED's brightness appear more linear
+    // Note this range matches with the wrap value
+    pwm_set_gpio_level(PICO_DEFAULT_LED_PIN, fade * fade);
+}
+#endif
+int main() {
+#ifndef PICO_DEFAULT_LED_PIN
+#warning pwm/led_fade example requires a board with a regular LED
+#else
+    // Tell the LED pin that the PWM is in charge of its value.
+    gpio_set_function(PICO_DEFAULT_LED_PIN, GPIO_FUNC_PWM);
+    // Figure out which slice we just connected to the LED pin
+    uint slice_num = pwm_gpio_to_slice_num(PICO_DEFAULT_LED_PIN);
+    // Mask our slice's IRQ output into the PWM block's single interrupt line,
+    // and register our interrupt handler
+    pwm_clear_irq(slice_num);
+    pwm_set_irq_enabled(slice_num, true);
+    irq_set_exclusive_handler(PWM_IRQ_WRAP, on_pwm_wrap);
+    irq_set_enabled(PWM_IRQ_WRAP, true);
+    // Get some sensible defaults for the slice configuration. By default, the
+    // counter is allowed to wrap over its maximum range (0 to 2**16-1)
+    pwm_config config = pwm_get_default_config();
+    // Set divider, reduces counter clock to sysclock/this value
+    pwm_config_set_clkdiv(&config, 4.f);
+    // Load the configuration into our PWM slice, and set it running.
+    pwm_init(slice_num, &config, true);
+    // Everything after this point happens in the PWM interrupt handler, so we
+    // can twiddle our thumbs
+    while (1)
+        tight_loop_contents();
+#endif
+}
+</code>
+## 返回目录
+[[pico_micropython|MicroPython编程PICO训练板]]