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64BIT STM32 DRIVER HOW TO
64BIT STM32 DRIVER CODE

HT event received, first LED data were transferred, prepare third LED data to first 24 section, wait for TC event.

Prepare first LED data in first 24 section, prepare second LED data in second 24 section, start DMA transfer in circular mode and wait for HT event.

Send reset pulse, wait for TC event, DMA is in normal mode.

When we transfer all leds, we can simply stop the DMA transfer and configure reset pulse again to send 40 elements of all zeros for 50us low pulse. At this point, data for third led started to transfer from memory to PWM and we can use second part of our 2-LED array to configure forth LED data. Later, we will receive TC event, which means that second LED was successfully transferred to PWM and we no longer need second part of memory for second LED. When we receive HT event (half transfer of 48 elements transfered), we know that first LED was completely transferred to PWM and we no longer need this memory for it, thus we can start prepare memory for third LED. Next step is to start the DMA transfer in circular mode and wait for HT event. When we are configuring the first LED, we also need to prepare the same for second LED and fill second part of main buffer. To send 24bits we need 24 words only and according to bit values, we set duty-cycle to either 33% or 67%. Once we have the TC event, we can start preparing a data for first LED. This is transfered with DMA to PWM channel and we have to wait for TC event. On the beginning, memory is configured with all zeros for reset pulse. Single 48 words long array is used for data transfer, acting as double-buffer DMA. DMA is used to transfer data from memory to peripheral compare register for PWM output. Implementation is done using single timer + PWM output on one of its channels.

After PWM transfer, send 50us pulse again ( 40 periods at 800kHz).There is no dead-time between end of first led and beginning of second led!.Transfer 24 bits for each led of 33% (logical 0) or 67% (logical 1) duty-cycle on PWM.Before you start PWM sequence for all leds, 50us reset pulse (pulse low) is required ( 40 periods at 800kHz).To transfer data for 1 LED, you need 30us PWM signal must be 800kHz, or 1.25us per bit.I will not go deep into control sequence, to set color you basically need to respect rules below: To have information for all leds, we need 3 * leds_count big array with R0,G0,B0, R1,G1,B1, R2,G2,B2,… color structure.

LED memory footprintĮach LED has RGB format for color, which represents 24 bits of data (or 3 bytes). We will use this feature for our raw data for PWM for each LED. DMA in STM32 also supports circular mode, which basically means that once we are at the end of block transfer, DMA will start from the beginning of memory and will transfer more data (this is visible on picture below with left arrow). Since we are receiving 2 events in the middle/end of block, we can use single buffer DMA mode but interact with it as double buffer data. receive Transfer Complete event ( TC event) after all elements were transferred.receive Half-Transfer Complete event ( HT event) after 24 elements were transferred,.If we configure DMA to transfer 48 elements we will: They are called at the end of block transfer and in the middle of block transfer, respectively. Second option we have is to use single buffer mode and rely on DMA Transfer-Complete and Half-Transfer Complete events.

64BIT STM32 DRIVER CODE

Handling this may add some additional code in our project. In this mode, you have 2 memory addresses and DMA will switch between memories at the end of block transaction. Double buffering DMAĭMA hardware in all STM32 families allows you double buffering mode. All together we need 3 * LEDS_Count + 24 * sizeof(uint32) bytes.

STM32 hardware allows you good way to scale down this ram usage to 3 bytes per LED, which is 300 bytes at 100 leds = 32x more efficient! In addition to this memory, we also need temporary buffer to store 2 LED raw PWM data, used for DMA hardware. If you have 100 leds, that’s almost 10k of RAM. It uses 24 words of RAM for each LED, which is 96 bytes per LED. It is very well written, but it has one major issue. If you have no experience with WS2812B leds, I strongly recommend you to read the blog post. There is a good explanation, already available on the web.

64BIT STM32 DRIVER HOW TO

In this tutorial I will explain how to drive WS2812B with STM32 using TIM PWM and DMA peripherals in the most efficient way by using minimum amount of RAM, required to process all leds.