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stmhal: Improve pyb.freq to allow 8 and 16MHz (not usable with USB).

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Also restrict higher frequencies to have a VCO_OUT frequency below
432MHz, as specified in the datasheet.

Docs improved to list allowed frequencies, and explain about USB
stability.
This commit is contained in:
Damien George
2014-11-02 15:10:15 +00:00
parent 039887a0ac
commit 38bd762121
2 changed files with 118 additions and 63 deletions
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12
docs/library/pyb.rst
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@@ -103,6 +103,18 @@ Power related functions
supported and the largest supported frequency not greater than
the given sys_freq will be selected.
Supported frequencies are (in MHz): 8, 16, 24, 30, 32, 36, 40, 42, 48,
54, 56, 60, 64, 72, 84, 96, 108, 120, 144, 168.
8MHz uses the HSE (external crystal) directly and 16MHz uses the HSI
(internal oscillator) directly. The higher frequencies use the HSE to
drive the PLL (phase locked loop), and then use the output of the PLL.
Note that if you change the frequency while the USB is enabled then
the USB may become unreliable. It is best to change the frequency
in boot.py, before the USB peripheral is started. Also note that
frequencies below 36MHz do not allow the USB to function correctly.
.. function:: wfi()
Wait for an interrupt.