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Merge pull request #271 from stapelberg/st 

MIMXRT1062/LLD/PITv1: switch to internal SysTick clock (600 MHz ARM)
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Fabien Poussin 2021-04-05 01:39:28 +02:00 committed by GitHub
parent a9297a6b34 4df9abffc5
commit cec80982e4
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 17 additions and 14 deletions
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31
os/hal/ports/MIMXRT1062/LLD/PITv1/hal_st_lld.c
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@ -24,6 +24,8 @@
#include "hal.h"
#include "clock_config.h"
#if (OSAL_ST_MODE != OSAL_ST_MODE_NONE) || defined(__DOXYGEN__)
/*===========================================================================*/
@ -73,16 +75,6 @@ OSAL_IRQ_HANDLER(SysTick_Handler) {
/* Driver exported functions. */
/*===========================================================================*/
// ARM SysTick is used for most Ardiuno timing functions, delay(), millis(),
// micros(). SysTick can run from either the ARM core clock, or from an
// "external" clock. NXP documents it as "24 MHz XTALOSC can be the external
// clock source of SYSTICK" (RT1052 ref manual, rev 1, page 411). However,
// NXP actually hid an undocumented divide-by-240 circuit in the hardware, so
// the external clock is really 100 kHz. We use this clock rather than the
// ARM clock, to allow SysTick to maintain correct timing even when we change
// the ARM clock to run at different speeds.
#define SYSTICK_EXT_FREQ 100000
/**
* @brief Low level ST driver initialization.
*
@ -90,11 +82,22 @@ OSAL_IRQ_HANDLER(SysTick_Handler) {
*/
void st_lld_init(void) {
#if OSAL_ST_MODE == OSAL_ST_MODE_PERIODIC
/* Periodic systick mode, the Cortex-Mx internal systick timer is used
in this mode.*/
SysTick->LOAD = (SYSTICK_EXT_FREQ / OSAL_ST_FREQUENCY) - 1;
/* Periodic systick mode, the Cortex-M7 internal systick timer is used in this
mode.
Contrary to the Teensy 4 Arduino startup code, we use the internal 600 MHz
ARM clock instead of the external 100 kHz clock. They use the external
clock to make switching CPU frequencies easier, but this ChibiOS port does
not support switching CPU frequencies at all. When we want to add support,
we will just need to adjust the SysTick configuration accordingly.
Using the faster clock allows users to increase the CH_CFG_ST_FREQUENCY for
finer grained tick duration and thereby minimum sleep duration when using
chThdSleep: 10μs instead of 100μs. */
SysTick->LOAD = (BOARD_BOOTCLOCKRUN_CORE_CLOCK / OSAL_ST_FREQUENCY) - 1;
SysTick->VAL = 0;
SysTick->CTRL = SysTick_CTRL_TICKINT_Msk | SysTick_CTRL_ENABLE_Msk;
SysTick->CTRL = SysTick_CTRL_TICKINT_Msk | SysTick_CTRL_ENABLE_Msk | SysTick_CTRL_CLKSOURCE_Msk;
/* IRQ enabled.*/
nvicSetSystemHandlerPriority(HANDLER_SYSTICK, MIMXRT1062_ST_IRQ_PRIORITY);