drivers/ws281x: Add ESP32 support

drivers/Makefile.dep

@@ -788,6 +788,9 @@ ifneq (,$(filter ws281x,$(USEMODULE)))
     ifneq (,$(filter arch_native,$(FEATURES_USED)))
       USEMODULE += ws281x_vt100
     endif
+    ifneq (,$(filter arch_esp32,$(FEATURES_USED)))
+      USEMODULE += ws281x_esp32
+    endif
   endif
   ifneq (,$(filter ws281x_atmega,$(USEMODULE)))
     FEATURES_REQUIRED += arch_avr8

drivers/include/ws281x.h

@@ -15,7 +15,8 @@
  *
  * The WS2812 or SK6812 RGB LEDs, or more commonly known as NeoPixels, can be
  * chained so that a single data pin of the MCU can control an arbitrary number
- * of RGB LEDs.
+ * of RGB LEDs. This driver supports both the WS2812/SK6812 and the WS2812b
+ * LEDs.
  *
  * # Support
  *
@@ -36,6 +37,15 @@
  * @warning On 8MHz ATmegas, only pins at GPIO ports B, C, and D are supported.
  *          (On 16MHz ATmegas, any pin is fine.)
  *
+ * ## ESP32
+ *
+ * The ESP32 implementation is frequency independent, as frequencies above 80MHz
+ * are high enough to support big banging without assembly.
+ *
+ * ## Native/VT100
+ *
+ * The native (VT100) implementation writes the LED state to the console.
+ *
  * ### Usage
  *
  * Add the following to your `Makefile` to use the ATmega backend:

drivers/ws281x/esp32.c

@@ -0,0 +1,106 @@
+/*
+ * Copyright 2020 Christian Friedrich Coors
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     drivers_ws281x
+ *
+ * @{
+ *
+ * @file
+ * @brief       Implementation of `ws281x_write_buffer()` for the ESP32 CPU
+ *
+ * @author      Christian Friedrich Coors <me@ccoors.de>
+ *
+ * @}
+ */
+#include <assert.h>
+#include <errno.h>
+#include <stdint.h>
+#include <string.h>
+
+#include "ws281x.h"
+#include "ws281x_params.h"
+#include "ws281x_constants.h"
+#include "periph_cpu.h"
+#include "xtimer.h"
+#include "xtensa/core-macros.h"
+#include "soc/rtc.h"
+
+#define ENABLE_DEBUG (0)
+#include "debug.h"
+
+
+static inline __attribute__((always_inline)) uint32_t get_cycle_count(void) {
+    uint32_t ccount;
+    __asm__ __volatile__("rsr %0,ccount":"=a" (ccount));
+    return ccount;
+}
+
+void ws281x_write_buffer(ws281x_t *dev, const void *buf, size_t size)
+{
+    assert(dev);
+    const uint8_t *pos = buf;
+    const uint8_t *end = pos + size;
+
+    // Cycles
+    uint32_t total_cycles, one_on, one_off, zero_on, zero_off, on_wait, off_wait;
+
+    // Current frequency
+    rtc_cpu_freq_t freq = rtc_clk_cpu_freq_value(rtc_clk_cpu_freq_get());
+
+    total_cycles = freq / (NS_PER_SEC / WS281X_T_DATA_NS);
+    one_on = freq / (NS_PER_SEC / WS281X_T_DATA_ONE_NS);
+    one_off = total_cycles - one_on;
+    zero_on = freq / (NS_PER_SEC / WS281X_T_DATA_ZERO_NS);
+    zero_off = total_cycles - zero_on;
+
+    DEBUG("[ws281x] esp32 freq=%d total=%d\n", freq, total_cycles);
+    DEBUG("[ws281x] esp32 cycles %d/%d/%d/%d\n", one_on, one_off, zero_on, zero_off);
+
+    uint32_t current_wait = 0, start = 0;
+
+    while (pos < end) {
+        uint8_t data = *pos;
+        for (uint8_t cnt = 8; cnt > 0; cnt--) {
+            if (data & 0b10000000) {
+                on_wait = one_on;
+                off_wait = one_off;
+            }
+            else {
+                on_wait = zero_on;
+                off_wait = zero_off;
+            }
+            start = get_cycle_count();
+            gpio_set(dev->params.pin);
+            current_wait = start + on_wait;
+            while (get_cycle_count() < current_wait) { }
+            gpio_clear(dev->params.pin);
+            start = get_cycle_count();
+            current_wait = start + off_wait;
+            while (get_cycle_count() < current_wait) { }
+            data <<= 1;
+        }
+        pos++;
+    }
+}
+
+int ws281x_init(ws281x_t *dev, const ws281x_params_t *params)
+{
+    if (!dev || !params || !params->buf) {
+        return -EINVAL;
+    }
+
+    memset(dev, 0, sizeof(ws281x_t));
+    dev->params = *params;
+
+    if (gpio_init(dev->params.pin, GPIO_OUT)) {
+        return -EIO;
+    }
+
+    return 0;
+}

drivers/ws281x/include/ws281x_backend.h

@@ -32,6 +32,15 @@ extern "C" {
 #endif
 /** @} */
 
+/**
+ * @name    Properties of the ESP32 backend.
+ * @{
+ */
+#ifdef MODULE_WS281X_ESP32
+#define WS281X_HAVE_INIT                    (1)
+#endif
+/** @} */
+
 /**
  * @name    Properties of the VT100 terminal backend.
  * @{

drivers/ws281x/include/ws281x_constants.h

@@ -27,6 +27,23 @@ extern "C" {
  * @name    Timing parameters for WS2812/SK6812 RGB LEDs
  * @{
  */
+
+/**
+ * @brief   Data transmission time in nanoseconds
+ *
+ * For the SK6812, WS2812 and WS2812b this is 1.25 µs. This is the total time
+ * required to transmit one bit.
+ */
+#define WS281X_T_DATA_NS                (1250U)
+
+/**
+ * @brief The high-times in nanoseconds.
+ * @{
+ */
+#define WS281X_T_DATA_ONE_NS            (650U)
+#define WS281X_T_DATA_ZERO_NS           (325U)
+/**@}*/
+
 /**
  * @brief   Time in microseconds to pull the data line low to signal end of data
  *

tests/driver_ws281x/Makefile

@@ -7,11 +7,10 @@ N ?= 8
 
 USEMODULE += ws281x
 
-# Currently the ws281x only supports AVR-based platforms and native
-# (via VT100 terminals).
+# Currently the ws281x only supports AVR-based platforms, the ESP32
+# and native (via VT100 terminals).
 # See https://doc.riot-os.org/group__drivers__ws281x.html
 FEATURES_BLACKLIST += arch_arm
-FEATURES_BLACKLIST += arch_esp32
 FEATURES_BLACKLIST += arch_esp8266
 FEATURES_BLACKLIST += arch_mips32r2
 FEATURES_BLACKLIST += arch_msp430