yan xu / PololuLedStrip

WS2812B

Dependents:   high speed light Bracelet

Fork of PololuLedStrip by David Grayson

PololuLedStrip.cpp@19:46d7ab0ba3e7, 2013-10-09 (annotated)

Committer:
DavidEGrayson
Date:
Wed Oct 09 01:13:49 2013 +0000
Revision:
19:46d7ab0ba3e7
Parent:
17:91fb934a2166
Child:
22:2fcd4e3cd8ac
Changed the timing so that this library only supports the high-speed strips now.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
DavidEGrayson 1:102307d9b701 1 #include "PololuLedStrip.h"
DavidEGrayson 1:102307d9b701 2
DavidEGrayson 1:102307d9b701 3 bool PololuLedStrip::interruptFriendly = false;
DavidEGrayson 1:102307d9b701 4
DavidEGrayson 19:46d7ab0ba3e7 5 // The two timed delays, in units of half-cycles.
DavidEGrayson 19:46d7ab0ba3e7 6 uint8_t led_strip_write_delays[2];
DavidEGrayson 4:d3b60bd43811 7
DavidEGrayson 7:9a088f042ee0 8 void PololuLedStrip::calculateDelays()
DavidEGrayson 7:9a088f042ee0 9 {
DavidEGrayson 15:d69eebdee025 10 int f_mhz = SystemCoreClock / 1000000; // Clock frequency in MHz.
DavidEGrayson 14:672baf3cf941 11
DavidEGrayson 14:672baf3cf941 12 if (f_mhz <= 48)
DavidEGrayson 14:672baf3cf941 13 {
DavidEGrayson 19:46d7ab0ba3e7 14 // The delays below result in 360/1120 ns pulses and a 1880 ns period on the mbed NXP LPC11U24.
DavidEGrayson 14:672baf3cf941 15 led_strip_write_delays[0] = 0;
DavidEGrayson 14:672baf3cf941 16 led_strip_write_delays[1] = 0;
DavidEGrayson 14:672baf3cf941 17 }
DavidEGrayson 14:672baf3cf941 18 else
DavidEGrayson 14:672baf3cf941 19 {
DavidEGrayson 15:d69eebdee025 20 // Try to generally compute what the delays should be for a ide range of clock frequencies.
DavidEGrayson 14:672baf3cf941 21
DavidEGrayson 14:672baf3cf941 22 // The fudge factors below were experimentally chosen so that we would have
DavidEGrayson 19:46d7ab0ba3e7 23 // ~100/840 ns pulses and a ~1430 ns period on the mbed NXP LPC1768 (96 MHz Cortex-M3).
DavidEGrayson 17:91fb934a2166 24 // There seem to be some ~100 ns inconsistencies in the timing depending on which example program is
DavidEGrayson 17:91fb934a2166 25 // running; the most likely explanation is some kind of flash caching that affects the timing.
DavidEGrayson 14:672baf3cf941 26 // If you ever change these numbers, it is important to check the the subtractions below
DavidEGrayson 19:46d7ab0ba3e7 27 // will not overflow in the worst case (smallest possible f_mhz).
DavidEGrayson 19:46d7ab0ba3e7 28 led_strip_write_delays[0] = 750*f_mhz/1000 - 33;
DavidEGrayson 19:46d7ab0ba3e7 29 led_strip_write_delays[1] = 550*f_mhz/1000 - 20;
DavidEGrayson 15:d69eebdee025 30 }
DavidEGrayson 15:d69eebdee025 31
DavidEGrayson 15:d69eebdee025 32 // Convert from units of cycles to units of half-cycles; it makes the assembly faster.
DavidEGrayson 19:46d7ab0ba3e7 33 for(int i = 0; i < 2; i++)
DavidEGrayson 15:d69eebdee025 34 {
DavidEGrayson 15:d69eebdee025 35 led_strip_write_delays[i] <<= 1;
DavidEGrayson 12:b6df8ac053c8 36 }
DavidEGrayson 7:9a088f042ee0 37 }
DavidEGrayson 6:9d0530b7dae2 38
DavidEGrayson 1:102307d9b701 39 PololuLedStrip::PololuLedStrip(PinName pinName)
DavidEGrayson 1:102307d9b701 40 {
DavidEGrayson 1:102307d9b701 41 gpio_init(&gpio, pinName, PIN_OUTPUT);
DavidEGrayson 1:102307d9b701 42 }
DavidEGrayson 1:102307d9b701 43
DavidEGrayson 1:102307d9b701 44 void PololuLedStrip::write(rgb_color * colors, unsigned int count)
DavidEGrayson 1:102307d9b701 45 {
DavidEGrayson 8:1578776ceac5 46 calculateDelays();
DavidEGrayson 8:1578776ceac5 47
DavidEGrayson 1:102307d9b701 48 __disable_irq(); // Disable interrupts temporarily because we don't want our pulse timing to be messed up.
DavidEGrayson 7:9a088f042ee0 49
DavidEGrayson 1:102307d9b701 50 while(count--)
DavidEGrayson 1:102307d9b701 51 {
DavidEGrayson 9:6ffb85d69eaf 52 led_strip_write_color(colors, gpio.reg_set, gpio.reg_clr, gpio.mask);
DavidEGrayson 9:6ffb85d69eaf 53 colors++;
DavidEGrayson 9:6ffb85d69eaf 54
DavidEGrayson 1:102307d9b701 55 if (interruptFriendly)
DavidEGrayson 1:102307d9b701 56 {
DavidEGrayson 1:102307d9b701 57 __enable_irq();
DavidEGrayson 1:102307d9b701 58 __nop();
DavidEGrayson 1:102307d9b701 59 __nop();
DavidEGrayson 1:102307d9b701 60 __nop();
DavidEGrayson 1:102307d9b701 61 __disable_irq();
DavidEGrayson 1:102307d9b701 62 }
DavidEGrayson 1:102307d9b701 63 }
DavidEGrayson 1:102307d9b701 64
DavidEGrayson 1:102307d9b701 65 __enable_irq(); // Re-enable interrupts now that we are done.
DavidEGrayson 1:102307d9b701 66 wait_us(24); // Hold the line low for 24 microseconds to send the reset signal.
DavidEGrayson 9:6ffb85d69eaf 67
DavidEGrayson 9:6ffb85d69eaf 68 //*(gpio.reg_set) = gpio.mask;
DavidEGrayson 9:6ffb85d69eaf 69 //*(gpio.reg_clr) = gpio.mask;
DavidEGrayson 9:6ffb85d69eaf 70
DavidEGrayson 1:102307d9b701 71 }