File content as of revision 27:9a62663f3de2:

#include "PololuLedStrip.h"

// Our assembly code currently does not work with chip families like the STM32F4
// that use the same register and a different mask for setting and clearing
// outputs.
#ifdef GPIO_IP_WITHOUT_BRR
#error This chip is not supported: does not have separate registers for setting and clearing GPIO outputs.
#endif

bool PololuLedStrip::interruptFriendly = false;

// The two timed delays, in units of half-cycles.
uint8_t led_strip_write_delays[2];

void PololuLedStrip::calculateDelays()
{
    int f_mhz = SystemCoreClock / 1000000;   // Clock frequency in MHz.

    if (f_mhz <= 48)
    {
        // The delays below result in 360/1120 ns pulses and a 1880 ns period on the mbed NXP LPC11U24.        
        led_strip_write_delays[0] = 0;
        led_strip_write_delays[1] = 0;
    }
    else
    {
        // Try to generally compute what the delays should be for a wide range of clock frequencies.
        
        // The fudge factors below were experimentally chosen so that we would have
        // ~100 ns and ~840 ns pulses and a ~1430 ns period on the mbed NXP LPC1768 (96 MHz Cortex-M3).
        // There seem to be some ~100 ns inconsistencies in the timing depending on which example program is
        // running; the most likely explanation is some kind of flash caching that affects the timing.
        // If you ever change these numbers, it is important to check the the subtractions below
        // will not overflow in the worst case (smallest possible f_mhz).
        //
        // On an STM32F303K8 (72 MHz Cortex-M4), these delays give us ~170 ns and ~840 ns pulses
        // and a ~1595 ns period, and there were no timing differences between the two
        // example programs.
        led_strip_write_delays[0] = 750*f_mhz/1000 - 33;
        led_strip_write_delays[1] = 550*f_mhz/1000 - 20;    
    }
 
    // Convert from units of cycles to units of half-cycles; it makes the assembly faster.   
    led_strip_write_delays[0] <<= 1;
    led_strip_write_delays[1] <<= 1;
}

PololuLedStrip::PololuLedStrip(PinName pinName)
{
    gpio_init_out(&gpio, pinName);
}

void PololuLedStrip::write(rgb_color * colors, unsigned int count)
{
    uint8_t t;
    calculateDelays();
    
    __disable_irq();   // Disable interrupts temporarily because we don't want our pulse timing to be messed up.

    while(count--)
    {

#ifdef _POLOLU_ORDER_GRB
        //swap red and green for WS2812b strips
        t = colors->red;
        colors->red = colors->green;
        colors->green = t;
#endif

        led_strip_write_color(colors, gpio.reg_set, gpio.reg_clr, gpio.mask);
        colors++;
         
        if (interruptFriendly)
        {
            __enable_irq();
            __nop();
            __nop();
            __nop();
            __disable_irq();
        }
    }
        
    __enable_irq();   // Re-enable interrupts now that we are done.
    wait_us(80);      // Send the reset signal.
}