altos/stm: Make sure we switch to MSI during timer init

Need to ensure that the CPU is actually using the MSI during timer
init or all of the other clock changes won't work

Signed-off-by: Keith Packard <keithp@keithp.com>

diff --git a/src/stm/ao_timer.c b/src/stm/ao_timer.c
index 5cf1e4a87dd37ab88be0c562e38ff1b78f699384..34f9edb90b084d40b5fbee14cdca7d313a03d30c 100644 (file)
--- a/src/stm/ao_timer.c
+++ b/src/stm/ao_timer.c
@@ -90,7 +90,15 @@ ao_clock_init(void)
        /* Switch to MSI while messing about */
        stm_rcc.cr |= (1 << STM_RCC_CR_MSION);
        while (!(stm_rcc.cr & (1 << STM_RCC_CR_MSIRDY)))
-               asm("nop");
+               ao_arch_nop();
+
+       stm_rcc.cfgr = (stm_rcc.cfgr & ~(STM_RCC_CFGR_SW_MASK << STM_RCC_CFGR_SW)) |
+               (STM_RCC_CFGR_SW_MSI << STM_RCC_CFGR_SW);
+
+       /* wait for system to switch to MSI */
+       while ((stm_rcc.cfgr & (STM_RCC_CFGR_SWS_MASK << STM_RCC_CFGR_SWS)) !=
+              (STM_RCC_CFGR_SWS_MSI << STM_RCC_CFGR_SWS))
+               ao_arch_nop();
 
        /* reset SW, HPRE, PPRE1, PPRE2, MCOSEL and MCOPRE */
        stm_rcc.cfgr &= (uint32_t)0x88FFC00C;
@@ -141,7 +149,6 @@ ao_clock_init(void)
        stm_flash.acr |= (1 << STM_FLASH_ACR_PRFEN);
 
        /* Enable 1 wait state so the CPU can run at 32MHz */
-       /* (haven't managed to run the CPU at 32MHz yet, it's at 16MHz) */
        stm_flash.acr |= (1 << STM_FLASH_ACR_LATENCY);
 
        /* Enable power interface clock */