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drivers/leds/ws2812: make frequency selection more flexible

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Previously only 4 MHz and 8 MHz were allowed. Given the tolerance
allowed in the WS2812 timing spec, frequency ranges around those
two can be used too which is useful for boards in which it is
difficult to generate those specific frequencies.
This commit is contained in:
Diego Herranz 2020-12-07 08:22:01 +00:00 committed by Brennan Ashton
parent 8a9f995d40
commit 441180b08c
1 changed files with 32 additions and 10 deletions
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42
drivers/leds/ws2812.c
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@ -39,21 +39,43 @@
* Pre-processor Definitions
****************************************************************************/
/* These are the tuning parameters to meet timing requirements */
/* In order to meet the signaling timing requirements, the waveforms required
* to represent a 0/1 symbol are created by specific SPI bytes defined here.
*
* Only two target frequencies: 4 MHz and 8 MHz. However, given the tolerance
* allowed in the WS2812 timing specs, two ranges around those target
* frequencies can be used for better flexibility. Extreme frequencies rounded
* to the nearest multiple of 100 kHz which meets the specs. Try to avoid
* using the extreme frequencies.
*
* If using an LED different to the WS2812 (e.g. WS2812B) check its timing
* specs, which may vary slightly, to decide which frequency is safe to use.
*
* WS2812 specs:
* T0H range: 200ns - 500ns
* T1H range: 550ns - 850ns
* Reset: low signal >50us
*/
#if CONFIG_WS2812_FREQUENCY == 4000000
# define WS2812_RST_CYCLES 30 /* 60us (>50us) */
# define WS2812_ZERO_BYTE 0b01000000 /* 250 ns (200ns - 500ns) */
# define WS2812_ONE_BYTE 0b01110000 /* 750 ns (550ns - 850ns) */
#elif CONFIG_WS2812_FREQUENCY == 8000000
# define WS2812_RST_CYCLES 60 /* 60us (>50us) */
# define WS2812_ZERO_BYTE 0b01100000 /* 250 ns (200ns - 500ns) */
# define WS2812_ONE_BYTE 0b01111100 /* 625 ns (550ns - 850ns) */
#if CONFIG_WS2812_FREQUENCY >= 3600000 && CONFIG_WS2812_FREQUENCY <= 5000000
# define WS2812_ZERO_BYTE 0b01000000 /* 200ns at 5 MHz, 278ns at 3.6 MHz */
# define WS2812_ONE_BYTE 0b01110000 /* 600ns at 5 MHz, 833ns at 3.6 MHz */
#elif CONFIG_WS2812_FREQUENCY >= 5900000 && CONFIG_WS2812_FREQUENCY <= 9000000
# define WS2812_ZERO_BYTE 0b01100000 /* 222ns at 9 MHz, 339ns at 5.9 MHz */
# define WS2812_ONE_BYTE 0b01111100 /* 556ns at 9 MHz, 847ns at 5.9 MHz */
#else
# error "Unsupported SPI Frequency"
#endif
#define WS2812_BYTES_PER_LED 8 * 3
/* Reset bytes
* Number of empty bytes to create the reset low pulse
* Aiming for 60 us, safely above the 50us required.
*/
#define WS2812_RST_CYCLES (CONFIG_WS2812_FREQUENCY * 60 / 1000000 / 8)
#define WS2812_BYTES_PER_LED (8 * 3)
#define WS2812_RW_PIXEL_SIZE 4
/* Transmit buffer looks like: