Diff: mbed/PololuLedStrip/PololuLedStrip.cpp

Revision:

0:e0dbd261724a

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed/PololuLedStrip/PololuLedStrip.cpp	Thu Dec 05 20:34:10 2019 -0500
@@ -0,0 +1,76 @@
+#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)
+{
+    calculateDelays();
+
+    __disable_irq();   // Disable interrupts temporarily because we don't want our pulse timing to be messed up.
+
+    while(count--)
+    {
+        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.
+}
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