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Clockless updates using SysTick
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@PaulZC
PaulZC committed Apr 9, 2020
1 parent dcd774f commit 1baa14e
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Showing 2 changed files with 98 additions and 39 deletions.
18 changes: 16 additions & 2 deletions platforms.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@
#ifdef __cplusplus
extern "C" {
#endif
// NOTE: Update platforms.cpp in root of FastLED library if this changes
// NOTE: Update platforms.cpp in root of FastLED library if this changes
#if defined(FASTLED_NRF52_ENABLE_PWM_INSTANCE0)
void PWM0_IRQHandler(void) { isrCount++; PWM_Arbiter<0>::isr_handler(); }
#endif
Expand All @@ -34,7 +34,21 @@

#endif // defined(NRF52_SERIES)


// ISR for the APOLLO3 SysTick
#if defined(FASTLED_APOLLO3)

// SysTick Interrupt Service Routine
#ifdef __cplusplus
extern "C" {
#endif
void SysTick_Handler(void) {
// We don't actually need to do anything in the ISR. There just needs to be one!
}
#ifdef __cplusplus
}
#endif

#endif // defined(FASTLED_APOLLO3)

// FASTLED_NAMESPACE_BEGIN
// FASTLED_NAMESPACE_END
119 changes: 82 additions & 37 deletions platforms/apollo3/clockless_apollo3.h
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Original file line number Diff line number Diff line change
Expand Up @@ -5,14 +5,14 @@ FASTLED_NAMESPACE_BEGIN

#if defined(FASTLED_APOLLO3)

//#include "ap3_analog.h"
#include "am_hal_systick.h"
#define FASTLED_HAS_CLOCKLESS 1

#ifndef SYSTICK_MAX_TICKS
#define SYSTICK_MAX_TICKS ((1 << 24)-1)
#endif
#define DO_RGBW // Uncomment this line to enable support for (e.g.) SK6812RGBW that need extra white bits

#define FASTLED_HAS_CLOCKLESS 1
#ifdef DO_RGBW
// Set all the white LEDs to this level. (What were you expecting for free!? ;-)
#define WHITE_LEVEL 1
#endif

template <int DATA_PIN, int T1, int T2, int T3, EOrder RGB_ORDER = RGB, int XTRA0 = 0, bool FLIP = false, int WAIT_TIME = 50>
class ClocklessController : public CPixelLEDController<RGB_ORDER> {
Expand All @@ -23,81 +23,120 @@ class ClocklessController : public CPixelLEDController<RGB_ORDER> {

public:
virtual void init() {
// Initialize everything
// This is _very_ SparkFun Artemis / Ambiq Micro Apollo3 Blue specific!

// Configure DATA_PIN for FastGPIO (settings are in fastpin_apollo3.h)
FastPin<DATA_PIN>::setOutput();
FastPin<DATA_PIN>::lo();
am_hal_clkgen_control(AM_HAL_CLKGEN_CONTROL_SYSCLK_MAX, 0);
am_hal_systick_load(0x00FFFFFF);
am_hal_systick_int_enable();
am_hal_interrupt_master_enable();
am_hal_systick_start();

// Make sure the system clock is running at the full 48MHz
am_hal_clkgen_control(AM_HAL_CLKGEN_CONTROL_SYSCLK_MAX, 0);

// Make sure interrupts are enabled
am_hal_interrupt_master_enable();

// Enable SysTick Interrupts in the NVIC
NVIC_EnableIRQ(SysTick_IRQn);

// SysTick is 24-bit and counts down (not up)

// Stop the SysTick (just in case it is already running).
// This clears the ENABLE bit in the SysTick Control and Status Register (SYST_CSR).
// In Ambiq naming convention: the control register is SysTick->CTRL
am_hal_systick_stop();

// Call SysTick_Config
// This is defined in core_cm4.h
// It loads the specified LOAD value into the SysTick Reload Value Register (SYST_RVR)
// In Ambiq naming convention: the reload register is SysTick->LOAD
// It sets the SysTick interrupt priority
// It clears the SysTick Current Value Register (SYST_CVR)
// In Ambiq naming convention: the current value register is SysTick->VAL
// Finally it sets these bits in the SysTick Control and Status Register (SYST_CSR):
// CLKSOURCE: SysTick uses the processor clock
// TICKINT: When the count reaches zero, the SysTick exception (interrupt) is changed to pending
// ENABLE: Enables the counter
// SysTick_Config returns 0 if successful. 1 indicates a failure (the LOAD value was invalid).
SysTick_Config(0xFFFFFFUL); // The LOAD value needs to be 24-bit
}

// extern "C" void am_systick_isr(void)
// {
// am_hal_systick_reset();
// }
virtual uint16_t getMaxRefreshRate() const { return 400; } // This can probably be increased?

virtual uint16_t getMaxRefreshRate() const { return 400; }
static void SysTick_Handler(void) {
// We don't actually need to do anything in the ISR. There just needs to be one!
}

protected:

virtual void showPixels(PixelController<RGB_ORDER> & pixels) {
//mWait.wait();
mWait.wait();
if(!showRGBInternal(pixels)) {
//sei(); delayMicroseconds(WAIT_TIME); cli();
//showRGBInternal(pixels);
sei(); delayMicroseconds(WAIT_TIME); cli();
showRGBInternal(pixels);
}
//mWait.mark();
mWait.mark();
}

// SysTick counts down not up and is 24-bit, so let's ex-or it so it appears to count up
#define am_hal_systick_count_inverted() (am_hal_systick_count() ^ 0xFFFFFF)

template<int BITS> __attribute__ ((always_inline)) inline static void writeBits(register uint32_t & next_mark, register uint8_t & b) {
for(register uint32_t i = BITS-1; i > 0; i--) {
while(am_hal_systick_count() < next_mark);
next_mark = am_hal_systick_count() + 10;//(T1+T2+T3);
//if (next_mark > SYSTICK_MAX_TICKS) { next_mark = next_mark - SYSTICK_MAX_TICKS; }
// SysTick counts down (not up) and is 24-bit
for(register uint32_t i = BITS-1; i > 0; i--) { // We could speed this up by using Bit Banding
while(am_hal_systick_count_inverted() < next_mark);
next_mark = (am_hal_systick_count_inverted() + T1+T2+T3) & 0xFFFFFF;
// (This will glitch when next_mark would normally exceed 0xFFFFFF)
FastPin<DATA_PIN>::hi();
if(b&0x80) {
while((next_mark - am_hal_systick_count()) > 5);//(T3+(200*(F_CPU/24000000))));
while((next_mark - am_hal_systick_count_inverted()) > (T3));//+(2*(F_CPU/24000000))));
FastPin<DATA_PIN>::lo();
} else {
while((next_mark - am_hal_systick_count()) > 7);//(T2+T3+(200*(F_CPU/24000000))));
while((next_mark - am_hal_systick_count_inverted()) > (T2+T3));//+(2*(F_CPU/24000000))));
FastPin<DATA_PIN>::lo();
}
b <<= 1;
}

while(am_hal_systick_count() < next_mark);
next_mark = am_hal_systick_count() + 10;//(T1+T2+T3);
//if (next_mark > SYSTICK_MAX_TICKS) { next_mark = next_mark - SYSTICK_MAX_TICKS; }
while(am_hal_systick_count_inverted() < next_mark);
next_mark = (am_hal_systick_count_inverted() + T1+T2+T3) & 0xFFFFFF;
// (This will glitch when next_mark would normally exceed 0xFFFFFF)
FastPin<DATA_PIN>::hi();
if(b&0x80) {
while((next_mark - am_hal_systick_count()) > 5);//(T3+(200*(F_CPU/24000000))));
while((next_mark - am_hal_systick_count_inverted()) > (T3));//+(2*(F_CPU/24000000))));
FastPin<DATA_PIN>::lo();
} else {
while((next_mark - am_hal_systick_count()) > 7);//(T2+T3+(200*(F_CPU/24000000))));
while((next_mark - am_hal_systick_count_inverted()) > (T2+T3));//+(2*(F_CPU/24000000))));
FastPin<DATA_PIN>::lo();
}
}

// This method is made static to force making register Y available to use for data on AVR - if the method is non-static, then
// gcc will use register Y for the this pointer.
static uint32_t showRGBInternal(PixelController<RGB_ORDER> pixels) {
FastPin<DATA_PIN>::lo();

// Setup the pixel controller and load/scale the first byte
pixels.preStepFirstByteDithering();
register uint8_t b = pixels.loadAndScale0();

// The SysTick ISR appears not be working so let's manually reload the SysTick VAL
//am_hal_systick_load(0xFFFFFF);

cli();
register uint32_t next_mark = am_hal_systick_count() + 10;//(T1+T2+T3);
if (next_mark > SYSTICK_MAX_TICKS) { next_mark = next_mark - SYSTICK_MAX_TICKS; }
// Calculate next_mark (the time of the next DATA_PIN transition)
// SysTick counts down (not up) and is 24-bit so let's use the inverted version and mask it to 24 bits
// (This will glitch when next_mark would normally exceed 0xFFFFFF)
register uint32_t next_mark = (am_hal_systick_count_inverted() + T1+T2+T3) & 0xFFFFFF;

while(pixels.has(1)) {
pixels.stepDithering();

#if (FASTLED_ALLOW_INTERRUPTS == 1)
cli();
// if interrupts took longer than 45µs, punt on the current frame
if(am_hal_systick_count() > next_mark) {
if((am_hal_systick_count() - next_mark) > ((WAIT_TIME-INTERRUPT_THRESHOLD)*CLKS_PER_US)) { sei(); return 0; }
if(am_hal_systick_count_inverted() > next_mark) { // Have we already missed the next_mark?
// If we have exceeded next_mark by an excessive amount, then bail (return 0)
if((am_hal_systick_count_inverted() - next_mark) > ((WAIT_TIME-INTERRUPT_THRESHOLD)*CLKS_PER_US)) { sei(); return 0; }
}
#endif

Expand All @@ -113,13 +152,19 @@ class ClocklessController : public CPixelLEDController<RGB_ORDER> {
writeBits<8+XTRA0>(next_mark, b);
b = pixels.advanceAndLoadAndScale0();

// Write the extra white bits if the RGBW strip needs them
#ifdef DO_RGBW
register uint8_t white_level = WHITE_LEVEL;
writeBits<8+XTRA0>(next_mark, white_level);
#endif

#if (FASTLED_ALLOW_INTERRUPTS == 1)
sei();
#endif
};

sei();
return (am_hal_systick_count());
return (am_hal_systick_count_inverted());
}

};
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