drivers: led_strip: add WS2812 I2S-based driver

Add a driver implementation that uses the I2S peripheral.
Based off this blog post:
https://electronut.in/nrf52-i2s-ws2812/

Should help with zephyrproject-rtos#33505, zephyrproject-rtos#29877 and maybe zephyrproject-rtos#47780, as there is no garbage
data at the end of transmissions on nRF52832, and no gaps.

Signed-off-by: Jonathan Rico <[email protected]>

drivers/led_strip/CMakeLists.txt

@@ -6,4 +6,5 @@ zephyr_library_sources_ifdef(CONFIG_APA102_STRIP        apa102.c)
 zephyr_library_sources_ifdef(CONFIG_LPD880X_STRIP       lpd880x.c)
 zephyr_library_sources_ifdef(CONFIG_WS2812_STRIP_GPIO   ws2812_gpio.c)
 zephyr_library_sources_ifdef(CONFIG_WS2812_STRIP_SPI    ws2812_spi.c)
+zephyr_library_sources_ifdef(CONFIG_WS2812_STRIP_I2S    ws2812_i2s.c)
 zephyr_library_sources_ifdef(CONFIG_TLC5971_STRIP       tlc5971.c)

drivers/led_strip/Kconfig.ws2812

@@ -26,6 +26,14 @@ config WS2812_STRIP_SPI
 	  The SPI driver is portable, but requires significantly more
 	  memory (1 byte of overhead per bit of pixel data).
 
+config WS2812_STRIP_I2S
+	bool "I2S driver"
+	depends on I2S
+	help
+	  Uses the I2S peripheral, memory usage is 4 bytes per color,
+	  times the number of pixels. A few more for the start and end
+	  delay. The reset delay has a coarse resolution of ~20us.
+
 config WS2812_STRIP_GPIO
 	bool "GPIO driver"
 	# Only an Cortex-M0 inline assembly implementation for the nRF51

drivers/led_strip/ws2812_i2s.c

@@ -0,0 +1,265 @@
+/*
+ * Copyright (c) 2022 Jonathan Rico
+ *
+ * Adapted from the SPI driver, using the procedure in this blog post:
+ * https://electronut.in/nrf52-i2s-ws2812/
+ *
+ * Note: the word "word" refers to a 32-bit integer unless otherwise stated.
+ *
+ * WS/LRCK frequency:
+ * This refers to the "I2S word or channel select" clock.
+ * The I2C peripheral sends two 16-bit channel values for each clock period.
+ * A single LED color (8 data bits) will take up one 32-bit word or one LRCK
+ * period. This means a standard RGB led will take 3 LRCK periods to transmit.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#define DT_DRV_COMPAT worldsemi_ws2812_i2s
+
+#include <string.h>
+
+#include <zephyr/drivers/led_strip.h>
+
+#define LOG_LEVEL CONFIG_LED_STRIP_LOG_LEVEL
+#include <zephyr/logging/log.h>
+LOG_MODULE_REGISTER(ws2812_i2s);
+
+#include <zephyr/device.h>
+#include <zephyr/drivers/i2s.h>
+#include <zephyr/dt-bindings/led/led.h>
+#include <zephyr/kernel.h>
+#include <zephyr/sys/util.h>
+
+#define WS2812_I2S_PRE_DELAY_WORDS 1
+
+struct ws2812_i2s_cfg {
+	struct device const *dev;
+	size_t tx_buf_bytes;
+	struct k_mem_slab *mem_slab;
+	uint8_t num_colors;
+	const uint8_t *color_mapping;
+	uint16_t reset_words;
+	uint32_t lrck_period;
+	uint32_t extra_wait_time_us;
+	bool active_low;
+	uint8_t nibble_one;
+	uint8_t nibble_zero;
+};
+
+/* Serialize an 8-bit color channel value into two 16-bit I2S values (or 1 32-bit
+ * word).
+ */
+static inline void ws2812_i2s_ser(uint32_t *word, uint8_t color, const uint8_t sym_one,
+				  const uint8_t sym_zero)
+{
+	*word = 0;
+	for (uint16_t i = 0; i < 8; i++) {
+		if ((1 << i) & color) {
+			*word |= sym_one << (i * 4);
+		} else {
+			*word |= sym_zero << (i * 4);
+		}
+	}
+
+	/* Swap the two I2S values due to the (audio) channel TX order. */
+	*word = (*word >> 16) | (*word << 16);
+}
+
+static int ws2812_strip_update_rgb(const struct device *dev, struct led_rgb *pixels,
+				   size_t num_pixels)
+{
+	const struct ws2812_i2s_cfg *cfg = dev->config;
+	uint8_t sym_one, sym_zero;
+	uint32_t reset_word;
+	uint32_t *tx_buf;
+	uint32_t flush_time_us;
+	void *mem_block;
+	int ret;
+
+	if (cfg->active_low) {
+		sym_one = (~cfg->nibble_one) & 0x0F;
+		sym_zero = (~cfg->nibble_zero) & 0x0F;
+		reset_word = 0xFFFFFFFF;
+	} else {
+		sym_one = cfg->nibble_one & 0x0F;
+		sym_zero = cfg->nibble_zero & 0x0F;
+		reset_word = 0;
+	}
+
+	/* Acquire memory for the I2S payload. */
+	ret = k_mem_slab_alloc(cfg->mem_slab, &mem_block, K_SECONDS(10));
+	if (ret < 0) {
+		LOG_ERR("Unable to allocate mem slab for TX (err %d)", ret);
+		return -ENOMEM;
+	}
+	tx_buf = (uint32_t *)mem_block;
+
+	/* Add a pre-data reset, so the first pixel isn't skipped by the strip. */
+	for (uint16_t i = 0; i < WS2812_I2S_PRE_DELAY_WORDS; i++) {
+		*tx_buf = reset_word;
+		tx_buf++;
+	}
+
+	/*
+	 * Convert pixel data into I2S frames. Each frame has pixel data
+	 * in color mapping on-wire format (e.g. GRB, GRBW, RGB, etc).
+	 */
+	for (uint16_t i = 0; i < num_pixels; i++) {
+		for (uint16_t j = 0; j < cfg->num_colors; j++) {
+			uint8_t pixel;
+
+			switch (cfg->color_mapping[j]) {
+			/* White channel is not supported by LED strip API. */
+			case LED_COLOR_ID_WHITE:
+				pixel = 0;
+				break;
+			case LED_COLOR_ID_RED:
+				pixel = pixels[i].r;
+				break;
+			case LED_COLOR_ID_GREEN:
+				pixel = pixels[i].g;
+				break;
+			case LED_COLOR_ID_BLUE:
+				pixel = pixels[i].b;
+				break;
+			default:
+				return -EINVAL;
+			}
+			ws2812_i2s_ser(tx_buf, pixel, sym_one, sym_zero);
+			tx_buf++;
+		}
+	}
+
+	for (uint16_t i = 0; i < cfg->reset_words; i++) {
+		*tx_buf = reset_word;
+		tx_buf++;
+	}
+
+	/* Flush the buffer on the wire. */
+	ret = i2s_write(cfg->dev, mem_block, cfg->tx_buf_bytes);
+	if (ret < 0) {
+		k_mem_slab_free(cfg->mem_slab, &mem_block);
+		LOG_ERR("Failed to write data: %d", ret);
+		return ret;
+	}
+
+	ret = i2s_trigger(cfg->dev, I2S_DIR_TX, I2S_TRIGGER_START);
+	if (ret < 0) {
+		LOG_ERR("Failed to trigger command %d on TX: %d", I2S_TRIGGER_START, ret);
+		return ret;
+	}
+
+	ret = i2s_trigger(cfg->dev, I2S_DIR_TX, I2S_TRIGGER_DRAIN);
+	if (ret < 0) {
+		LOG_ERR("Failed to trigger command %d on TX: %d", I2S_TRIGGER_DRAIN, ret);
+		return ret;
+	}
+
+	/* Wait until transaction is over */
+	flush_time_us = cfg->lrck_period * cfg->tx_buf_bytes / sizeof(uint32_t);
+	k_usleep(flush_time_us + cfg->extra_wait_time_us);
+
+	return ret;
+}
+
+static int ws2812_strip_update_channels(const struct device *dev, uint8_t *channels,
+					size_t num_channels)
+{
+	LOG_ERR("update_channels not implemented");
+	return -ENOTSUP;
+}
+
+static int ws2812_i2s_init(const struct device *dev)
+{
+	const struct ws2812_i2s_cfg *cfg = dev->config;
+	struct i2s_config config;
+	uint32_t lrck_hz;
+	int ret;
+
+	lrck_hz = USEC_PER_SEC / (cfg->lrck_period);
+	LOG_DBG("Word clock: freq %u Hz period %u us",
+		lrck_hz, cfg->lrck_period);
+
+	/* 16-bit stereo, 100kHz LCLK */
+	config.word_size = 16;
+	config.channels = 2;
+	config.format = I2S_FMT_DATA_FORMAT_I2S;
+	config.options = I2S_OPT_BIT_CLK_MASTER | I2S_OPT_FRAME_CLK_MASTER;
+	config.frame_clk_freq = lrck_hz; /* WS (or LRCK) */
+	config.mem_slab = cfg->mem_slab;
+	config.block_size = cfg->tx_buf_bytes;
+	config.timeout = 1000;
+
+	ret = i2s_configure(cfg->dev, I2S_DIR_TX, &config);
+	if (ret < 0) {
+		LOG_ERR("Failed to configure I2S device: %d\n", ret);
+		return ret;
+	}
+
+	for (uint16_t i = 0; i < cfg->num_colors; i++) {
+		switch (cfg->color_mapping[i]) {
+		case LED_COLOR_ID_WHITE:
+		case LED_COLOR_ID_RED:
+		case LED_COLOR_ID_GREEN:
+		case LED_COLOR_ID_BLUE:
+			break;
+		default:
+			LOG_ERR("%s: invalid channel to color mapping."
+				"Check the color-mapping DT property",
+				dev->name);
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
+static const struct led_strip_driver_api ws2812_i2s_api = {
+	.update_rgb = ws2812_strip_update_rgb,
+	.update_channels = ws2812_strip_update_channels,
+};
+
+/* Integer division, but always rounds up: e.g. 10/3 = 4 */
+#define WS2812_ROUNDED_DIVISION(x, y) ((x + (y - 1)) / y)
+
+#define WS2812_I2S_LRCK_PERIOD_US(idx) DT_INST_PROP(idx, lrck_period)
+
+#define WS2812_RESET_DELAY_US(idx)    DT_INST_PROP(idx, reset_delay)
+/* Rounds up to the next 20us. */
+#define WS2812_RESET_DELAY_WORDS(idx) WS2812_ROUNDED_DIVISION(WS2812_RESET_DELAY_US(idx), \
+							      WS2812_I2S_LRCK_PERIOD_US(idx))
+
+#define WS2812_NUM_COLORS(idx) (DT_INST_PROP_LEN(idx, color_mapping))
+
+#define WS2812_I2S_NUM_PIXELS(idx) (DT_INST_PROP(idx, chain_length))
+
+#define WS2812_I2S_BUFSIZE(idx)                                                                    \
+	(((WS2812_NUM_COLORS(idx) * WS2812_I2S_NUM_PIXELS(idx)) +	                           \
+	  WS2812_I2S_PRE_DELAY_WORDS + WS2812_RESET_DELAY_WORDS(idx)) * 4)
+
+#define WS2812_I2S_DEVICE(idx)                                                                     \
+                                                                                                   \
+	K_MEM_SLAB_DEFINE_STATIC(ws2812_i2s_##idx##_slab, WS2812_I2S_BUFSIZE(idx), 2, 4);          \
+                                                                                                   \
+	static const uint8_t ws2812_i2s_##idx##_color_mapping[] =                                  \
+		DT_INST_PROP(idx, color_mapping);                                                  \
+                                                                                                   \
+	static const struct ws2812_i2s_cfg ws2812_i2s_##idx##_cfg = {                              \
+		.dev = DEVICE_DT_GET(DT_INST_PROP(idx, i2s_dev)),                                  \
+		.tx_buf_bytes = WS2812_I2S_BUFSIZE(idx),                                           \
+		.mem_slab = &ws2812_i2s_##idx##_slab,                                              \
+		.num_colors = WS2812_NUM_COLORS(idx),                                              \
+		.color_mapping = ws2812_i2s_##idx##_color_mapping,                                 \
+		.lrck_period = WS2812_I2S_LRCK_PERIOD_US(idx),                                     \
+		.extra_wait_time_us = DT_INST_PROP(idx, extra_wait_time),                          \
+		.reset_words = WS2812_RESET_DELAY_WORDS(idx),                                      \
+		.active_low = DT_INST_PROP(idx, out_active_low),                                   \
+		.nibble_one = DT_INST_PROP(idx, nibble_one),                                       \
+		.nibble_zero = DT_INST_PROP(idx, nibble_zero),                                     \
+	};                                                                                         \
+                                                                                                   \
+	DEVICE_DT_INST_DEFINE(idx, ws2812_i2s_init, NULL, NULL, &ws2812_i2s_##idx##_cfg,           \
+			      POST_KERNEL, CONFIG_LED_STRIP_INIT_PRIORITY, &ws2812_i2s_api);
+
+DT_INST_FOREACH_STATUS_OKAY(WS2812_I2S_DEVICE)

dts/bindings/led_strip/worldsemi,ws2812-i2s.yaml

@@ -0,0 +1,43 @@
+# Copyright (c) 2022 Jonathan Rico
+# SPDX-License-Identifier: Apache-2.0
+
+description: |
+  Worldsemi WS2812 LED strip, I2S binding
+
+  Driver bindings for controlling a WS2812 or compatible LED
+  strip with an I2S master.
+
+compatible: "worldsemi,ws2812-i2s"
+
+include: [base.yaml, ws2812.yaml]
+
+properties:
+
+  i2s-dev:
+    type: phandle
+    required: true
+    description: Pointer to the I2S instance.
+
+  out-active-low:
+    type: boolean
+    description: True if the output pin is active low.
+
+  nibble-one:
+    type: int
+    default: 0x0E
+    description: 4-bit value to shift out for a 1 pulse.
+
+  nibble-zero:
+    type: int
+    default: 0x08
+    description: 4-bit value to shift out for a 0 pulse.
+
+  lrck-period:
+    type: int
+    default: 10
+    description: LRCK (left/right clock) period in microseconds.
+
+  extra-wait-time:
+    type: int
+    default: 300
+    description: Extra microseconds to wait for the driver to flush its I2S queue.