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sys: make early MCK init actually work

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Felix Kopp 2020-12-02 00:27:48 +01:00
parent b5dc88c966
commit c222c35fe5
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GPG key ID: C478BA0A85F75728
2 changed files with 11 additions and 3 deletions
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2
arch/at91sam3x8e/startup.c
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@ -24,7 +24,7 @@ extern uint32_t _eheap; /* heap end */
/* implementation in init/main.c */
void do_bootstrap(void);
/* implementation in sys.c */
void sys_init();
void sys_init(void);
__naked void irq_reset(void)
{

12
arch/at91sam3x8e/sys.c
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@ -8,7 +8,16 @@
#include <ardix/string.h>
#include <toolchain.h>
uint32_t sys_core_clock = 4000000UL; /* default internal 4MHz RC oscillator */
/*
* The initial sys_core_clock on system boot would actually be 4000000 because
* the 4 MHz RC oscillator is used by default. However, for performance
* reasons, the system core clock is configured to use the 84 MHz PLLA clock
* even before the memory area for global variables (like this one) is copied
* from flash to RAM, which in turn would overwrite any updates to the clock.
* So, since we trust the clock to be configured correctly before this global
* variable is accessed anywhere, we initialize it to the 84 MHz clock.
*/
uint32_t sys_core_clock = 84000000UL;
int sys_init(void)
{
@ -75,7 +84,6 @@ int sys_init(void)
| REG_PMC_MCKR_CSS_VAL(2 /* = PLLA clock */);
mom_are_we_there_yet(REG_PMC_SR & REG_PMC_SR_MCKRDY_BIT);
sys_core_clock = 84000000UL;
return 0;
}