Commit 3c1645ce authored by Rahix's avatar Rahix
Browse files

Merge 'Implement proper delays for Pycardium'

Closes #177

See merge request card10/firmware!324
parents d06941b8 dbeec980
......@@ -31,6 +31,11 @@ void pycardium_hal_init(void)
* a character becomes available.
*/
epic_interrupt_enable(EPIC_INT_UART_RX);
/*
* Configure SysTick timer for 1ms period.
*/
SysTick_Config(SystemCoreClock / 1000);
}
/******************************************************************************
......@@ -120,18 +125,148 @@ void mp_hal_set_interrupt_char(char c)
}
}
/******************************************************************************
* SysTick timer at 1000 Hz
*/
static volatile uint64_t systick_count = 0;
void SysTick_Handler(void)
{
systick_count += 1;
}
/*
* Get an absolute "timestamp" in microseconds.
*/
static uint64_t systick_get_us()
{
uint32_t irqsaved = __get_PRIMASK();
__set_PRIMASK(0);
uint64_t counts_per_us = SystemCoreClock / 1000000;
uint64_t us = systick_count * 1000 +
(SysTick->LOAD - SysTick->VAL) / counts_per_us;
__set_PRIMASK(irqsaved);
return us;
}
static void systick_delay_precise(uint32_t us)
{
/*
* Calculate how long the busy-spin needs to be. As the very first
* instruction, read the current timer value to ensure as little skew as
* possible.
*
* Subtract 0.3us (constant_offset) to account for the duration of the
* calculations.
*/
uint32_t count_to_overflow = SysTick->VAL;
uint32_t count_reload = SysTick->LOAD;
uint32_t clocks_per_us = SystemCoreClock / 1000000;
uint32_t constant_offset = clocks_per_us * 3 / 10;
uint32_t delay_count = us * clocks_per_us - constant_offset;
/*
* Calculate the final count for both paths. Marked as volatile so the
* compiler can't move this into the branches and screw up the timing.
*/
volatile uint32_t count_final_direct = count_to_overflow - delay_count;
volatile uint32_t count_final_underflow =
count_reload - (delay_count - count_to_overflow);
if (delay_count > count_to_overflow) {
/*
* Wait for the SysTick to underflow and then count down
* to the final value.
*/
while (SysTick->VAL <= count_to_overflow ||
SysTick->VAL > count_final_underflow) {
__NOP();
}
} else {
/*
* Wait for the SysTick to count down to the final value.
*/
while (SysTick->VAL > count_final_direct) {
__NOP();
}
}
}
static void systick_delay_sleep(uint32_t us)
{
uint64_t final_time = systick_get_us() + (uint64_t)us - 2;
while (1) {
uint64_t now = systick_get_us();
if (now >= final_time) {
break;
}
/*
* Sleep with WFI if more than 1ms of delay is remaining. The
* SysTick interrupt is guaranteed to happen within any timespan
* of 1ms.
*
* Use a critical section encompassing both the check and the
* WFI to prevent a race-condition where the interrupt happens
* just in between the check and WFI.
*/
uint32_t irqsaved = __get_PRIMASK();
__set_PRIMASK(0);
if ((now + 1000) < final_time) {
__WFI();
}
__set_PRIMASK(irqsaved);
/*
* Handle pending MicroPython 'interrupts'. This call could
* potentially not return here when a handler raises an
* exception. Those will propagate outwards and thus make the
* delay return early.
*
* One example of this happeing is the KeyboardInterrupt
* (CTRL+C) which will abort the running code and exit to REPL.
*/
mp_handle_pending();
}
}
static void systick_delay(uint32_t us)
{
if (us == 0)
return;
/*
* For very short delays, use the systick_delay_precise() function which
* delays with a microsecond accuracy. For anything >1ms, use
* systick_delay_sleep() which puts the CPU to sleep when nothing is
* happening and also checks for MicroPython interrupts every now and
* then.
*/
if (us < 1000) {
systick_delay_precise(us);
} else {
systick_delay_sleep(us);
}
}
/******************************************************************************
* Time & Delay
*/
void mp_hal_delay_ms(mp_uint_t ms)
{
mxc_delay(ms * 1000);
systick_delay(ms * 1000);
}
void mp_hal_delay_us(mp_uint_t us)
{
mxc_delay(us);
systick_delay(us);
}
mp_uint_t mp_hal_ticks_ms(void)
......
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