yan xu / PololuLedStrip

WS2812B

Dependents:   high speed light Bracelet

Fork of PololuLedStrip by David Grayson

PololuLedStrip.cpp@17:91fb934a2166, 2013-03-01 (annotated)

Committer:
DavidEGrayson
Date:
Fri Mar 01 05:13:23 2013 +0000
Revision:
17:91fb934a2166
Parent:
16:eaed541b08b0
Child:
19:46d7ab0ba3e7
Not sure.

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 15:d69eebdee025 5 // The three timed delays, in units of half-cycles.
DavidEGrayson 7:9a088f042ee0 6 uint8_t led_strip_write_delays[3];
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 14:672baf3cf941 14 // The delays below result in 800/1590 ns pulses and a 2500 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 15:d69eebdee025 17 led_strip_write_delays[2] = 5;
DavidEGrayson 14:672baf3cf941 18 }
DavidEGrayson 14:672baf3cf941 19 else
DavidEGrayson 14:672baf3cf941 20 {
DavidEGrayson 15:d69eebdee025 21 // Try to generally compute what the delays should be for a ide range of clock frequencies.
DavidEGrayson 14:672baf3cf941 22
DavidEGrayson 14:672baf3cf941 23 // The fudge factors below were experimentally chosen so that we would have
DavidEGrayson 17:91fb934a2166 24 // ~700/1300 ns pulses and a ~2500 ns period on the mbed NXP LPC1768 (96 MHz Cortex-M3).
DavidEGrayson 17:91fb934a2166 25 // There seem to be some ~100 ns inconsistencies in the timing depending on which example program is
DavidEGrayson 17:91fb934a2166 26 // running; the most likely explanation is some kind of flash caching that affects the timing.
DavidEGrayson 14:672baf3cf941 27 // If you ever change these numbers, it is important to check the the subtractions below
DavidEGrayson 15:d69eebdee025 28 // will not overflow in the worst case, which is f_mhz = 49.
DavidEGrayson 15:d69eebdee025 29 led_strip_write_delays[0] = 700*f_mhz/1000 - 23;
DavidEGrayson 16:eaed541b08b0 30 led_strip_write_delays[1] = 600*f_mhz/1000 - 18;
DavidEGrayson 16:eaed541b08b0 31 led_strip_write_delays[2] = 1200*f_mhz/1000 - 33;
DavidEGrayson 15:d69eebdee025 32 }
DavidEGrayson 15:d69eebdee025 33
DavidEGrayson 15:d69eebdee025 34 // Convert from units of cycles to units of half-cycles; it makes the assembly faster.
DavidEGrayson 15:d69eebdee025 35 for(int i = 0; i < 3; i++)
DavidEGrayson 15:d69eebdee025 36 {
DavidEGrayson 15:d69eebdee025 37 led_strip_write_delays[i] <<= 1;
DavidEGrayson 12:b6df8ac053c8 38 }
DavidEGrayson 7:9a088f042ee0 39 }
DavidEGrayson 6:9d0530b7dae2 40
DavidEGrayson 1:102307d9b701 41 PololuLedStrip::PololuLedStrip(PinName pinName)
DavidEGrayson 1:102307d9b701 42 {
DavidEGrayson 1:102307d9b701 43 gpio_init(&gpio, pinName, PIN_OUTPUT);
DavidEGrayson 1:102307d9b701 44 }
DavidEGrayson 1:102307d9b701 45
DavidEGrayson 1:102307d9b701 46 void PololuLedStrip::write(rgb_color * colors, unsigned int count)
DavidEGrayson 1:102307d9b701 47 {
DavidEGrayson 8:1578776ceac5 48 calculateDelays();
DavidEGrayson 8:1578776ceac5 49
DavidEGrayson 1:102307d9b701 50 __disable_irq(); // Disable interrupts temporarily because we don't want our pulse timing to be messed up.
DavidEGrayson 7:9a088f042ee0 51
DavidEGrayson 1:102307d9b701 52 while(count--)
DavidEGrayson 1:102307d9b701 53 {
DavidEGrayson 9:6ffb85d69eaf 54 led_strip_write_color(colors, gpio.reg_set, gpio.reg_clr, gpio.mask);
DavidEGrayson 9:6ffb85d69eaf 55 colors++;
DavidEGrayson 9:6ffb85d69eaf 56
DavidEGrayson 1:102307d9b701 57 if (interruptFriendly)
DavidEGrayson 1:102307d9b701 58 {
DavidEGrayson 1:102307d9b701 59 __enable_irq();
DavidEGrayson 1:102307d9b701 60 __nop();
DavidEGrayson 1:102307d9b701 61 __nop();
DavidEGrayson 1:102307d9b701 62 __nop();
DavidEGrayson 1:102307d9b701 63 __disable_irq();
DavidEGrayson 1:102307d9b701 64 }
DavidEGrayson 1:102307d9b701 65 }
DavidEGrayson 1:102307d9b701 66
DavidEGrayson 1:102307d9b701 67 __enable_irq(); // Re-enable interrupts now that we are done.
DavidEGrayson 1:102307d9b701 68 wait_us(24); // Hold the line low for 24 microseconds to send the reset signal.
DavidEGrayson 9:6ffb85d69eaf 69
DavidEGrayson 9:6ffb85d69eaf 70 //*(gpio.reg_set) = gpio.mask;
DavidEGrayson 9:6ffb85d69eaf 71 //*(gpio.reg_clr) = gpio.mask;
DavidEGrayson 9:6ffb85d69eaf 72
DavidEGrayson 1:102307d9b701 73 }