pico: add "neopixel" led support (WS2812)

.gitignore

@@ -23,7 +23,7 @@ bld/
 build/
 build.stm32/
 build.mingw/
-cmake-build-debug/
+cmake-build-*/
 [Bb]in/
 [Oo]bj/
 [Ll]og/

32blit-pico/CMakeLists.txt

@@ -148,6 +148,7 @@ pico_sdk_init()
 # generate PIO headers (has to be after SDK init)
 pico_generate_pio_header(BlitHalPico ${CMAKE_CURRENT_LIST_DIR}/st7789.pio)
 pico_generate_pio_header(BlitHalPico ${CMAKE_CURRENT_LIST_DIR}/spi.pio)
+pico_generate_pio_header(BlitHalPico ${CMAKE_CURRENT_LIST_DIR}/ws2812.pio)
 
 # include picovision drivers
 if(BLIT_DISPLAY_DRIVER STREQUAL "picovision")

32blit-pico/led.cpp

@@ -13,6 +13,24 @@
 #if defined(LED_R_PIN) && defined(LED_G_PIN) && defined(LED_B_PIN)
 static const int led_pins[]{LED_R_PIN, LED_G_PIN, LED_B_PIN};
 #define HAVE_LED
+#elif defined(LED_WS2812_PIN)
+#include "hardware/pio.h"
+#include "ws2812.pio.h"
+
+static uint32_t last_color = 0;
+static int pio_sm = -1;
+
+static void put_pixel(uint8_t r, uint8_t g, uint8_t b, uint8_t a) {
+  if(pio_sm < 0) return;
+  uint32_t color =
+          (((uint32_t)((r * a) >> 8) << 8)
+          | ((uint32_t)((g * a) >> 8) << 16)
+          | (uint32_t)((b * a) >> 8)) << 8u;
+  if(color != last_color) {
+    pio_sm_put_blocking(pio0, 0, color);
+    last_color = color;
+  }
+}
 #endif
 
 void init_led() {
@@ -31,6 +49,18 @@ void init_led() {
   bi_decl(bi_1pin_with_name(led_pins[0], "Red LED"));
   bi_decl(bi_1pin_with_name(led_pins[1], "Green LED"));
   bi_decl(bi_1pin_with_name(led_pins[2], "Blue LED"));
+#elif defined(LED_WS2812_PIN)
+  PIO pio = pio0;
+  uint pio_offset = pio_add_program(pio, &ws2812_program);
+  pio_sm = pio_claim_unused_sm(pio, false);
+  if(pio_sm > -1) {
+    ws2812_program_init(pio, pio_sm, pio_offset, LED_WS2812_PIN, 800000, true);
+    pio_sm_put_blocking(pio, 0, 0);
+  } else {
+    printf("LED_WS2812: could not find a free pio sm\r\n");
+  }
+
+  bi_decl(bi_1pin_with_name(LED_WS2812_PIN, "NeoPixel RGB LED (WS2812)"));
 #endif
 }
 
@@ -45,5 +75,7 @@ void update_led() {
   pwm_set_gpio_level(led_pins[1], value);
   value = (uint16_t)(std::pow((float)(api.LED.b) / 255.0f, gamma) * 65535.0f + 0.5f);
   pwm_set_gpio_level(led_pins[2], value);
+#elif defined(LED_WS2812_PIN)
+  put_pixel(api.LED.r, api.LED.g, api.LED.b, api.LED.a);
 #endif
 }

32blit-pico/ws2812.pio

@@ -0,0 +1,48 @@
+;
+; Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+;
+; SPDX-License-Identifier: BSD-3-Clause
+;
+
+.program ws2812
+.side_set 1
+
+.define public T1 2
+.define public T2 5
+.define public T3 3
+
+.lang_opt python sideset_init = pico.PIO.OUT_HIGH
+.lang_opt python out_init     = pico.PIO.OUT_HIGH
+.lang_opt python out_shiftdir = 1
+
+.wrap_target
+bitloop:
+    out x, 1       side 0 [T3 - 1] ; Side-set still takes place when instruction stalls
+    jmp !x do_zero side 1 [T1 - 1] ; Branch on the bit we shifted out. Positive pulse
+do_one:
+    jmp  bitloop   side 1 [T2 - 1] ; Continue driving high, for a long pulse
+do_zero:
+    nop            side 0 [T2 - 1] ; Or drive low, for a short pulse
+.wrap
+
+% c-sdk {
+#include "hardware/clocks.h"
+
+static inline void ws2812_program_init(PIO pio, uint sm, uint offset, uint pin, float freq, bool rgbw) {
+
+    pio_gpio_init(pio, pin);
+    pio_sm_set_consecutive_pindirs(pio, sm, pin, 1, true);
+
+    pio_sm_config c = ws2812_program_get_default_config(offset);
+    sm_config_set_sideset_pins(&c, pin);
+    sm_config_set_out_shift(&c, false, true, rgbw ? 32 : 24);
+    sm_config_set_fifo_join(&c, PIO_FIFO_JOIN_TX);
+
+    int cycles_per_bit = ws2812_T1 + ws2812_T2 + ws2812_T3;
+    float div = clock_get_hz(clk_sys) / (freq * cycles_per_bit);
+    sm_config_set_clkdiv(&c, div);
+
+    pio_sm_init(pio, sm, offset, &c);
+    pio_sm_set_enabled(pio, sm, true);
+}
+%}