How to control neopixel (ws2812b)

maxlapshin · March 8, 2023, 10:34am

I want to add matek 2812 led strip to pixracer r15 and it seems that it is neopixel.

I cannot find implementation of neopixel_write in source code. Where is it?
I cannot find, where is configured output pin? Where does neopixel_write sends its data and how can I configure it?
How can I publish data to neopixel instance? I see that it takes something from led_controller, but I cannot understand where does the data comes from?

JulianOes · March 9, 2023, 9:28pm

This one? PX4-Autopilot/src/drivers/lights/neopixel/neopixel.cpp at 55563eba49f87624d7b73356ea3d421fee7ec081 · PX4/PX4-Autopilot · GitHub

Ah, it’s a bit hidden, and here:

github.com

PX4/PX4-Autopilot/blob/bd5838faf0730b40d5d971b798563c82eeecdb5f/platforms/nuttx/src/px4/stm/stm32_common/srgbled_dma/srgbled_dma.cpp

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Good question. Have a look through these files. I’m not sure. Maybe @david_s5 can give you a hint.

It looks like LedController is consuming the uORB led_control topic.

github.com

PX4/PX4-Autopilot/blob/e6eed4364860345de1dcab81ecfa2530e87aa00a/src/lib/led/led.h#L184


      
          
          			if (priority[next_priority].blink_times_left == 0) {
          				// handle infinite case
          				priority[next_priority].blink_times_left = 254;
          			}
          		}
          	};
          
          	PerLedData _states[BOARD_MAX_LEDS]; ///< keep current LED states
          
          	uORB::Subscription _led_control_sub{ORB_ID(led_control)}; ///< uorb subscription
          	uORB::SubscriptionInterval _parameter_update_sub{ORB_ID(parameter_update), 1_s};
          
          	hrt_abstime _last_update_call{0};
          
          	perf_counter_t _led_control_sub_lost_perf{perf_alloc(PC_COUNT, MODULE_NAME": led_control message missed")};
          
          	uint8_t _max_brightness{UINT8_MAX};
          
          	bool _force_update{true}; ///< force an orb_copy in the beginning
          	bool _breathe_enabled{false}; ///< true if at least one of the led's is currently in breathe mode

maxlapshin · March 10, 2023, 6:54am

great response! Thanks a lot!! Will try to dig deeper

david_s5 · March 10, 2023, 7:36am

The driver uses DMA operations on a Timer.

This is how it is chosen:

github.com

PX4/PX4-Autopilot/blob/55563eba49f87624d7b73356ea3d421fee7ec081/boards/cuav/can-gps-v1/src/board_config.h#L82-L94


      
          /* USE_S_RGB_LED_DMAis passed in from the *.cmake file
           * Bootloader is not timming sensitive and can use the SW version as a
           * size savings
           * The Application can not as it needs DMA to maintain reall time.
           */
          
          
#if defined(USE_S_RGB_LED_DMA)
          #  define S_RGB_LED_DMA              DMAMAP_TIM1_CH2
          #  define S_RGB_LED_TIMER                1   /* timer 1    */
          #  define S_RGB_LED_CHANNEL              2   /* channel 2  */
          #  define S_RGB_LED_CHANNELN             1   /* channel 2N */
          #  define S_RGB_LED_TIM_GPIO             GPIO_TIM1_CH2N_1
          #endif

Timer and channel choices is configured here:

github.com

PX4/PX4-Autopilot/blob/55563eba49f87624d7b73356ea3d421fee7ec081/platforms/nuttx/src/px4/stm/stm32_common/srgbled_dma/srgbled_dma.cpp#L241-L314


      
          #if S_RGB_LED_CHANNEL == 1
          # define SLED_CCER      (CCER_CCnxE << 0) |
          # define SLED_CCMR1     GTIM_CCMR1_OC1PE | (GTIM_CCMR_MODE_PWM1 << GTIM_CCMR1_OC1M_SHIFT)
          # define SLED_CCMR2     0
          # define SLED_rCCR      rCCR1
          #elif S_RGB_LED_CHANNEL == 2
          # define SLED_CCER      (CCER_CCnxE << 4)
          # define SLED_CCMR1     GTIM_CCMR1_OC2PE | (GTIM_CCMR_MODE_PWM1 << GTIM_CCMR1_OC2M_SHIFT)
          # define SLED_CCMR2     0
          # define SLED_rCCR      rCCR2
          #elif S_RGB_LED_CHANNEL == 3
          # define SLED_CCER      (CCER_CCnxE << 8)
          # define SLED_CCMR1     0
          # define SLED_CCMR2     GTIM_CCMR1_OC1PE | (GTIM_CCMR_MODE_PWM1 << GTIM_CCMR1_OC1M_SHIFT)
          # define SLED_rCCR      rCCR3
          #elif S_RGB_LED_CHANNEL == 4
          # define SLED_CCER      (CCER_CCnxE << 12)
          # define SLED_CCMR1     0
          # define SLED_CCMR2     GTIM_CCMR1_OC2PE | (GTIM_CCMR_MODE_PWM1 << GTIM_CCMR1_OC2M_SHIFT)
          # define SLED_rCCR      rCCR4

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Here is the init

github.com

PX4/PX4-Autopilot/blob/55563eba49f87624d7b73356ea3d421fee7ec081/platforms/nuttx/src/px4/stm/stm32_common/srgbled_dma/srgbled_dma.cpp#L455


      
          	rDIER |= ATIM_DIER_CC1DE << (S_RGB_LED_CHANNEL - 1);
          
          
	SLED_rCCR = 0;
          
          
	// Down count, edge aligned PWN 1 wiht auto reload
          
          
	rCR1 = GTIM_CR1_ARPE | GTIM_CR1_EDGE | GTIM_CR1_DIR;
          
          
	// Set up the GPIO
          
          
	stm32_configgpio(S_RGB_LED_TIM_GPIO);
          
          
	// Get a DMA channel.
          
          
	dma_handle = stm32_dmachannel(S_RGB_LED_DMA);
          
          
	return (dma_handle == nullptr) ? -1 : 0;
          }
          
          
int neopixel_deinit()
          {

maxlapshin · March 12, 2023, 5:09pm

In all sources I’ve found S_RGB_LED_TIM_GPIO only on cuav/can-gps-v1
Does it mean that pixracer r15 doesn’t have proper hardware for plugging this led or it means that it is just not configured?

I’m not using any regular frsky telemetry or radio input, only mavlink via TELEM1, so maybe it is possible to reuse some free pin in these connectors for this task? Sorry if this question looks dumb, I’m not aware of details of DMA in STM32.

If there are no proper free pins in pixracer, then my way is to have a separate arduino working as UART peer or i2c slave doing this controlling?