From 676fa2bc556d06750374fe456484a1338c9e7bd9 Mon Sep 17 00:00:00 2001
From: Rahix <rahix@rahix.de>
Date: Thu, 3 Oct 2019 14:43:21 +0200
Subject: [PATCH] fix(pycardium): Implement proper delays
The old delay implementation is based on `mxc_delay`, provided by the
SDK. This implementation has issues, as details in #177. To fix these
issues, `mxc_delay` is replaced with a re-implementation which polls the
MicroPython scheduler and calls `wfi` when we can safely sleep.
The SysTick timer is configured globally (on core 1) to tick every 80ms.
This seems to be a reasonable value to allow at least some `wfi`-sleep
in the bounds used by most apps.
Signed-off-by: Rahix <rahix@rahix.de>
---
pycardium/mphalport.c | 88 ++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 86 insertions(+), 2 deletions(-)
diff --git a/pycardium/mphalport.c b/pycardium/mphalport.c
index 60cd9df0..61ea9def 100644
--- a/pycardium/mphalport.c
+++ b/pycardium/mphalport.c
@@ -31,6 +31,17 @@ void pycardium_hal_init(void)
* a character becomes available.
*/
epic_interrupt_enable(EPIC_INT_UART_RX);
+
+ /*
+ * Configure SysTick timer.
+ *
+ * Reload is configured for 80ms. This seems to be a reasonable value
+ * to allow at least some sleep for common sleep times in apps.
+ */
+ SysTick->LOAD = 7679999 & SysTick_LOAD_RELOAD_Msk;
+ SysTick->VAL = 1;
+ SysTick->CTRL = SysTick_CTRL_ENABLE_Msk | SysTick_CTRL_CLKSOURCE_Msk |
+ SysTick_CTRL_TICKINT_Msk;
}
/******************************************************************************
@@ -124,16 +135,80 @@ void mp_hal_set_interrupt_char(char c)
* Time & Delay
*/
+static volatile uint32_t delay_overflows = 0;
+
+/*
+ * A delay implementation based on the SysTick timer.
+ */
+static void systick_delay_us(uint32_t us)
+{
+ if (us == 0) {
+ return;
+ }
+
+ uint32_t starttick = SysTick->VAL;
+ uint32_t ticks = (uint32_t)(
+ ((uint64_t)us * (uint64_t)SystemCoreClock) / 1000000
+ );
+ uint32_t reload = SysTick->LOAD + 1;
+ delay_overflows = ticks / reload;
+ uint32_t lasttick = ticks % reload;
+
+ uint32_t endtick;
+ if (lasttick >= starttick) {
+ delay_overflows += 1;
+ endtick = reload - (lasttick - starttick);
+ } else {
+ endtick = starttick - lasttick;
+ }
+
+ while (delay_overflows > 0) {
+ mp_handle_pending();
+ /*
+ * Overflow triggers the SysTick interrupt so we can sleep here.
+ *
+ * Note that this does **not** apply to the while-loop following
+ * this one.
+ */
+ __WFI();
+ }
+
+ while (SysTick->VAL > endtick) {
+ mp_handle_pending();
+ }
+}
+
+/*
+ * Interrupt handler needed for delay implementation. If we ever define a more
+ * sophisticated SysTick_Handler, make sure to include a call to this function!
+ */
+static void systick_delay_handler(void)
+{
+ if (SysTick->CTRL & SysTick_CTRL_COUNTFLAG_Msk) {
+ if (delay_overflows > 0) {
+ delay_overflows--;
+ }
+ }
+}
+
+/* HAL function for MicroPython */
void mp_hal_delay_ms(mp_uint_t ms)
{
- mxc_delay(ms * 1000);
+ systick_delay_us(ms * 1000);
}
+/* HAL function for MicroPython */
void mp_hal_delay_us(mp_uint_t us)
{
- mxc_delay(us);
+ systick_delay_us(us);
}
+/*
+ * HAL function for MicroPython
+ *
+ * This function is not really used except in a debug code-path of
+ * `parse_compile_execute`. Thus we need to define it as a stub.
+ */
mp_uint_t mp_hal_ticks_ms(void)
{
return 0;
@@ -163,3 +238,12 @@ int mp_hal_trng_read_int(void)
epic_trng_read((uint8_t *)&result, sizeof(result));
return result;
}
+
+/******************************************************************************
+ * SysTick Handler
+ */
+void SysTick_Handler(void)
+{
+ /* Needed for delay implementation */
+ systick_delay_handler();
+}
--
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