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cpu/samd5x: don't run DFLL on-demand

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The DFLL on samd5x has a hardware bug that requires a special
re-enabling sequence when it is disabled and then re-enabled again.

When running the clock on-demand, the hardware handles the disabling
and re-enabling so that sequence does not get executed.

To reproduce, run `tests/periph_uart` on `same54-xpro`.

Without this patch the test will get seemingly stuck on `sleep_test()`.
(In fact it keeps running, but the DFLL has the wrong frequency so the
UART baudrate is wrong).

In this test, on `same54-xpro` only UART0 is sourced from DFLL.
So if the UART is disabled the DFLL will be turned off as well.
This commit is contained in:
Benjamin Valentin 2020-04-02 20:11:41 +02:00
parent 4eb9b9b9df
commit 49fda3e900
1 changed files with 0 additions and 1 deletions
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cpu/samd5x/cpu.c
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@ -235,6 +235,5 @@ void cpu_init(void)
/* set ONDEMAND bit after all clocks have been configured */
/* This is to avoid setting the source for the main clock to ONDEMAND before using it. */
OSCCTRL->DFLLCTRLA.reg |= OSCCTRL_DFLLCTRLA_ONDEMAND;
OSCCTRL->Dpll[0].DPLLCTRLA.reg |= OSCCTRL_DPLLCTRLA_ONDEMAND;
}