Requires to configure system clock after back from stop mode manually in STM32L4 family

[Eman869]

Description

Currently, MSI is the default system clock after system wake up from stop mode. To wake up system from peripherals like LPUART, I2C, and SWPMI, HSI should be selected. A method to configure HSI as system clock after system wake up from stop mode is required.

Issue request type

[ ] Question
[X] Enhancement
[ ] Bug

[0xc0170]

@ARMmbed/team-st-mcd Please review
[Mirrored to Jira]

[bcostm]

The comment in this file says:

// On L4 platforms we've seen unstable PLL CLK configuraiton
// when DEEP SLEEP exits just few µs after being entered
// So we need to force MSI usage before setting clocks again

Yes the MSI is configured first but then the HSI is reconfigured again. Why this current implementation is not correct in your case ?

[Mirrored to Jira]

[0xc0170]

@Eman869 we need some additional info for this issue
[Mirrored to Jira]

[Eman869]

@bcostm What needed is not to re-configure clock, but to set the default clock as HSI after exiting STOP mode. Register RCC_CGFR, bit15 is related. MSI is not able to set as clock source for LPUART, I2C, and SWPMI.
[Mirrored to Jira]

[LMESTM]

@Eman869 in case of stressful tests of very fast exit and entries into deep sleep we have found issues that lead to errors on the clock stabilization and could lead to erroneous communication on peripherals like LP_UART. This was fixed in PR #6561 in order to fix #6513 and #6514 .
If you remove the stabilization time you may face those issues again.
[Mirrored to Jira]

[Eman869]

@LMESTM I had checked PR #6561 , I believe it is not the same thing. For STM32L4, MSI is the default system clock after stop mode/system reset. I am not going to remove the stabilization time, the delay must be kept if MSI was in PLL mode before entering stop mode. The issue #7317 is to have a configuration for users who would like to have HSI as the default system clock after stop mode, to make pr #7326 able to work in STOP mode when LPUART clock source is HSI.
[Mirrored to Jira]

[screamerbg]

@Eman869 @LMESTM Any follow up on this?
[Mirrored to Jira]

[adbridge]

Internal Jira reference: https://jira.arm.com/browse/IOTPART-5655

[jeromecoutant]

@Eman869 Are you expecting some development ?