Code: Select all

/**
 * =====================================================================
 * sets the WS2812 LED on a RP2040-Zero board using PWM and DMA
 * public domain code written by katak255 2025年10月30日
 * =====================================================================
 * - Thanks to Greg Chadwick's blog post and github code on PWM and DMA.
 * =====================================================================
 */
#include "pico/stdlib.h"
#include "hardware/dma.h"
#include "hardware/pwm.h"
/*
 * =====================================================================
 * WS2812 function
 * =====================================================================
 */
#define WS2812_PIN PICO_DEFAULT_WS2812_PIN
#define WS2812_DMA_SIZE 25 // 24 bits colour + idle
// PWM constants for 125MHz clk_sys (8ns clock)
//
#define WS2812_PWM_CLK 150 // 1200ns
#define WS2812_T1H_CLK 100 // 800ns
#define WS2812_T0H_CLK 50 // 400ns
// WS2812B version V5 specifies >280us, but who cares if 50us works
//
#define WS2812_RES_US 50
void ws2812_set(uint rgb)
{
 static uint ws_data[WS2812_DMA_SIZE];
 uint grb = ((rgb >> 8) & 0x00FF00)
 | ((rgb << 8) & 0xFF0000)
 | (rgb & 0x0000FF);
 // convert GRB colour value into PWM channel A CC data
 // - colour bits always have non-zero CC values
 // - the last data value of 0 idles the PWM output
 //
 for (int i = 0; i < (WS2812_DMA_SIZE - 1); i++) {
 ws_data[i] = (grb & 0x800000) ? WS2812_T1H_CLK : WS2812_T0H_CLK;
 grb <<= 1;
 }
 ws_data[WS2812_DMA_SIZE - 1] = 0;
 // set up and start PWM
 //
 gpio_set_function(WS2812_PIN, GPIO_FUNC_PWM);
 int ws_slice = pwm_gpio_to_slice_num(WS2812_PIN);
 pwm_set_wrap(ws_slice, WS2812_PWM_CLK - 1);
 pwm_set_gpio_level(WS2812_PIN, 0); // initially idle Low
 pwm_set_enabled(ws_slice, true); // start PWM
 // set up and start DMA
 // - 32-bit transfer, read increments, write fixed
 //
 int pdma = dma_claim_unused_channel(true);
 dma_channel_config pcfg = dma_channel_get_default_config(pdma);
 channel_config_set_transfer_data_size(&pcfg, DMA_SIZE_32);
 channel_config_set_read_increment(&pcfg, true);
 channel_config_set_write_increment(&pcfg, false);
 channel_config_set_dreq(&pcfg, DREQ_PWM_WRAP0 + ws_slice);
 dma_channel_configure(
 pdma,
 &pcfg,
 &pwm_hw->slice[ws_slice].cc, // write addr
 ws_data, // read addr
 WS2812_DMA_SIZE, // count
 true // start immediately
 );
 // wait for DMA to finish, then cleanup
 dma_channel_wait_for_finish_blocking(pdma);
 dma_channel_cleanup(pdma);
 dma_channel_unclaim(pdma);
 // a short pause for the WS2812 to reset
 // - no more High pulses after the last colour bit goes Low
 //
 busy_wait_us_32(WS2812_RES_US);
 pwm_set_enabled(ws_slice, false); // stop PWM
}
/*
 * =====================================================================
 * main
 * =====================================================================
 */
uint clr_dat[] = {
 0xFFFFFF, 0x808080, 0x404040, 0x202020,
 0xFF0000, 0x800000, 0x400000, 0x200000,
 0x00FF00, 0x008000, 0x004000, 0x002000,
 0x0000FF, 0x000080, 0x000040, 0x000020,
 0x000000
};
int main()
{
 // show some colours on the WS2812 LED
 //
 int pause = 1000;
forever:
 for (int i = 0; i < count_of(clr_dat); i++) {
 ws2812_set(clr_dat[i]);
 sleep_ms(pause);
 }
 if (pause == 125) pause = 1000; else pause /= 2;
 goto forever;
}

Code: Select all

 ...
 static uint16_t ws_data[WS2812_DMA_SIZE];
 ...
 channel_config_set_transfer_data_size(&pcfg, DMA_SIZE_16);
 ...

Code: Select all

/**
 * =====================================================================
 * sets the WS2812 LED on a RP2040-Zero board using PWM only
 * public domain code written by katak255 2025年11月01日
 * =====================================================================
 */
#include "pico/stdlib.h"
#include "hardware/dma.h"
/*
 * =====================================================================
 * WS2812 function
 * =====================================================================
 */
#define WS2812_PIN PICO_DEFAULT_WS2812_PIN
#define WS2812_DMA_SIZE (24 * 3)
// Notes on DMA timing and format:
// - for 125MHz clk_sys (8ns clock), DMA pacing is 50 cycles or 400ns
// - a colour bit consists of 3 DMA transfers in 1200ns
// - T1 is 2-High 1-Low while T0 is 1-High 2-Low
//
#define WS2812_DMA_DIV 50 // 8*50 == 400ns
// GPIO CTRL bits used are OEOVER and OUTOVER:
//
#define GPIO_CTRL_OEOVER_ENABLE (0x3u << 12) // output enable
#define GPIO_CTRL_OUTOVER_LOW (0x2u << 8) // output drive low
#define GPIO_CTRL_OUTOVER_HIGH (0x3u << 8) // output drive high
// WS2812B version V5 specifies >280us, but who cares if 50us works
//
#define WS2812_RES_US 50
void ws2812_set(uint rgb)
{
 static uint ws_data[WS2812_DMA_SIZE];
 uint grb = ((rgb >> 8) & 0x00FF00)
 | ((rgb << 8) & 0xFF0000)
 | (rgb & 0x0000FF);
 // GPIOn_CTRL values needed
 //
 uint v0 = io_bank0_hw->io[WS2812_PIN].ctrl; // original reg value
 uint v1 = v0 | GPIO_CTRL_OEOVER_ENABLE; // output enabled
 uint vL = v1 | GPIO_CTRL_OUTOVER_LOW; // enabled & Low
 uint vH = v1 | GPIO_CTRL_OUTOVER_HIGH; // enabled & High
 // convert GRB colour value into PWM data
 //
 for (int i = 0; i < WS2812_DMA_SIZE; ) {
 ws_data[i++] = vH;
 ws_data[i++] = (grb & 0x800000) ? vH : vL;
 ws_data[i++] = vL;
 grb <<= 1;
 }
 // set up and start DMA
 // - 32-bit transfer, read increments, write fixed
 //
 int pdma = dma_claim_unused_channel(true);
 dma_channel_config pcfg = dma_channel_get_default_config(pdma);
 channel_config_set_transfer_data_size(&pcfg, DMA_SIZE_32);
 channel_config_set_read_increment(&pcfg, true);
 channel_config_set_write_increment(&pcfg, false);
 int ptimer = dma_claim_unused_timer(true);
 dma_timer_set_fraction(ptimer, 1, WS2812_DMA_DIV);
 channel_config_set_dreq(&pcfg, dma_get_timer_dreq(ptimer));
 dma_channel_configure(
 pdma,
 &pcfg,
 &io_bank0_hw->io[WS2812_PIN].ctrl, // write addr
 ws_data, // read addr
 WS2812_DMA_SIZE, // count
 true // start immediately
 );
 // wait for DMA to finish, then cleanup
 dma_channel_wait_for_finish_blocking(pdma);
 dma_channel_cleanup(pdma);
 dma_timer_unclaim(ptimer);
 dma_channel_unclaim(pdma);
 // a short pause for the WS2812 to reset
 // - no more High pulses after the last colour bit goes Low
 //
 busy_wait_us_32(WS2812_RES_US);
 io_bank0_hw->io[WS2812_PIN].ctrl = v0; // restore GPIOn_CTRL
}
/*
 * =====================================================================
 * main
 * =====================================================================
 */
uint clr_dat[] = {
 0xFFFFFF, 0x808080, 0x404040, 0x202020,
 0xFF0000, 0x800000, 0x400000, 0x200000,
 0x00FF00, 0x008000, 0x004000, 0x002000,
 0x0000FF, 0x000080, 0x000040, 0x000020,
 0x000000
};
int main()
{
 // show some colours on the WS2812 LED
 //
 int pause = 1000;
forever:
 for (int i = 0; i < count_of(clr_dat); i++) {
 ws2812_set(clr_dat[i]);
 sleep_ms(pause);
 }
 if (pause == 125) pause = 1000; else pause /= 2;
 goto forever;
}