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Dec 10, 2019
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samd: neopixel: Fix neopixels after #2297 #2363

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157 changes: 63 additions & 94 deletions ports/atmel-samd/common-hal/neopixel_write/__init__.c
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Original file line number Diff line number Diff line change
Expand Up @@ -34,32 +34,70 @@
#ifdef SAMD51
#include "hri/hri_cmcc_d51.h"
#include "hri/hri_nvmctrl_d51.h"

// This magical macro makes sure the delay isn't optimized out and is the
// minimal three instructions.
#define delay_cycles(cycles) \
{ \
uint32_t t; \
asm volatile ( \
"movs %[t], %[c]\n\t" \
"loop%=:\n\t" \
"subs %[t], #1\n\t" \
"bne.n loop%=" : [t] "=r"(t) : [c] "I" (cycles)); \
}
#endif

// Ensure this code is compiled with -Os. Any other optimization level may change the timing of it
// and break neopixels.
#pragma GCC push_options
#pragma GCC optimize ("Os")
__attribute__((naked,noinline,aligned(16)))
static void neopixel_send_buffer_core(volatile uint32_t *clraddr, uint32_t pinMask,
const uint8_t *ptr, int numBytes);

static void neopixel_send_buffer_core(volatile uint32_t *clraddr, uint32_t pinMask,
const uint8_t *ptr, int numBytes) {
asm volatile(" push {r4, r5, r6, lr};"
" add r3, r2, r3;"
"loopLoad:"
" ldrb r5, [r2, #0];" // r5 := *ptr
" add r2, #1;" // ptr++
" movs r4, #128;" // r4-mask, 0x80
"loopBit:"
" str r1, [r0, #4];" // set
#ifdef SAMD21
" movs r6, #3; d2: sub r6, #1; bne d2;" // delay 3
#endif
#ifdef SAMD51
" movs r6, #3; d2: subs r6, #1; bne d2;" // delay 3
#endif
" tst r4, r5;" // mask&r5
" bne skipclr;"
" str r1, [r0, #0];" // clr
"skipclr:"
#ifdef SAMD21
" movs r6, #6; d0: sub r6, #1; bne d0;" // delay 6
#endif
#ifdef SAMD51
" movs r6, #6; d0: subs r6, #1; bne d0;" // delay 6
#endif
" str r1, [r0, #0];" // clr (possibly again, doesn't matter)
#ifdef SAMD21
" asr r4, r4, #1;" // mask >>= 1
#endif
#ifdef SAMD51
" asrs r4, r4, #1;" // mask >>= 1
#endif
" beq nextbyte;"
" uxtb r4, r4;"
#ifdef SAMD21
" movs r6, #2; d1: sub r6, #1; bne d1;" // delay 2
#endif
#ifdef SAMD51
" movs r6, #2; d1: subs r6, #1; bne d1;" // delay 2
#endif
" b loopBit;"
"nextbyte:"
" cmp r2, r3;"
" bcs neopixel_stop;"
" b loopLoad;"
"neopixel_stop:"
" pop {r4, r5, r6, pc};"
"");
}

uint64_t next_start_tick_ms = 0;
uint32_t next_start_tick_us = 1000;

void common_hal_neopixel_write(const digitalio_digitalinout_obj_t* digitalinout, uint8_t *pixels, uint32_t numBytes) {
// This is adapted directly from the Adafruit NeoPixel library SAMD21G18A code:
// https://github.com/adafruit/Adafruit_NeoPixel/blob/master/Adafruit_NeoPixel.cpp
uint8_t *ptr, *end, p, bitMask;
// and the asm version from https://github.com/microsoft/uf2-samdx1/blob/master/inc/neopixel.h
uint32_t pinMask;
PortGroup* port;

Expand All @@ -71,100 +109,32 @@ void common_hal_neopixel_write(const digitalio_digitalinout_obj_t* digitalinout,
mp_hal_disable_all_interrupts();


#ifdef SAMD21
// Make sure the NVM cache is consistently timed.
NVMCTRL->CTRLB.bit.READMODE = NVMCTRL_CTRLB_READMODE_DETERMINISTIC_Val;
#endif

#ifdef SAMD51
// When this routine is positioned at certain addresses, the timing logic
// below can be too fast by about 2.5x. This is some kind of (un)fortunate code
// positiong with respect to a cache line.
// positioning with respect to a cache line.
// Theoretically we should turn on off the CMCC caches and the
// NVM caches to ensure consistent timing. Testing shows the the NVMCTRL
// cache disabling seems to make the difference. But turn both off to make sure.
// It's difficult to test because additions to the code before the timing loop
// below change instruction placement. Testing was done by adding cache changes
// below the loop (so only the first time through is wrong).
// below change instruction placement. (though this should be less true now that
// the main code is in the cache-aligned function neopixel_send_buffer_core)
// Testing was done by adding cache changes below the loop (so only the
// first time through is wrong).
//
// Turn off instruction, data, and NVM caches to force consistent timing.
// Invalidate existing cache entries.
hri_cmcc_set_CFG_reg(CMCC, CMCC_CFG_DCDIS | CMCC_CFG_ICDIS);
hri_cmcc_write_MAINT0_reg(CMCC, CMCC_MAINT0_INVALL);
hri_nvmctrl_set_CTRLA_CACHEDIS0_bit(NVMCTRL);
hri_nvmctrl_set_CTRLA_CACHEDIS1_bit(NVMCTRL);
#endif
#endif

uint32_t pin = digitalinout->pin->number;
port = &PORT->Group[GPIO_PORT(pin)]; // Convert GPIO # to port register
pinMask = (1UL << (pin % 32)); // From port_pin_set_output_level ASF code.
ptr = pixels;
end = ptr + numBytes;
p = *ptr++;
bitMask = 0x80;

volatile uint32_t *set = &(port->OUTSET.reg),
*clr = &(port->OUTCLR.reg);

for(;;) {
*set = pinMask;
// This is the time where the line is always high regardless of the bit.
// For the SK6812 its 0.3us +- 0.15us
#ifdef SAMD21
asm("nop; nop;");
#endif
#ifdef SAMD51
delay_cycles(2);
#endif
if((p & bitMask) != 0) {
// This is the high delay unique to a one bit.
// For the SK6812 its 0.3us
#ifdef SAMD21
asm("nop; nop; nop; nop; nop; nop; nop;");
#endif
#ifdef SAMD51
delay_cycles(3);
#endif
*clr = pinMask;
} else {
*clr = pinMask;
// This is the low delay unique to a zero bit.
// For the SK6812 its 0.3us
#ifdef SAMD21
asm("nop; nop;");
#endif
#ifdef SAMD51
delay_cycles(2);
#endif
}
if((bitMask >>= 1) != 0) {
// This is the delay between bits in a byte and is the 1 code low
// level time from the datasheet.
// For the SK6812 its 0.6us +- 0.15us
#ifdef SAMD21
asm("nop; nop; nop; nop; nop;");
#endif
#ifdef SAMD51
delay_cycles(4);
#endif
} else {
if(ptr >= end) break;
p = *ptr++;
bitMask = 0x80;
// This is the delay between bytes. It's similar to the other branch
// in the if statement except its tuned to account for the time the
// above operations take.
// For the SK6812 its 0.6us +- 0.15us
#ifdef SAMD51
delay_cycles(3);
#endif
}
}

#ifdef SAMD21
// Speed up! (But inconsistent timing.)
NVMCTRL->CTRLB.bit.READMODE = NVMCTRL_CTRLB_READMODE_NO_MISS_PENALTY_Val;
#endif
volatile uint32_t *clr = &(port->OUTCLR.reg);
neopixel_send_buffer_core(clr, pinMask, pixels, numBytes);

#ifdef SAMD51
// Turn instruction, data, and NVM caches back on.
Expand All @@ -189,4 +159,3 @@ void common_hal_neopixel_write(const digitalio_digitalinout_obj_t* digitalinout,

}

#pragma GCC pop_options