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stmhal: Enhance pyb.freq to configure bus (AHB, APB1, APB2) freqs.

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This is useful if you need precise control over the speed of
peripherals (eg SPI clock).
This commit is contained in:
Damien George
2014-12-08 21:32:55 +00:00
parent 46c3ab2004
commit 008251180d
2 changed files with 58 additions and 22 deletions
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30
docs/library/pyb.rst
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@@ -93,26 +93,38 @@ Interrupt related functions
Power related functions
-----------------------
.. function:: freq([sys_freq])
.. function:: freq([sysclk[, hclk[, pclk1[, pclk2]]]])
If given no arguments, returns a tuple of clock frequencies:
(SYSCLK, HCLK, PCLK1, PCLK2).
If given an argument, sets the system frequency to that value in Hz.
Eg freq(120000000) gives 120MHz. Note that not all values are
supported and the largest supported frequency not greater than
the given sys_freq will be selected.
(sysclk, hclk, pclk1, pclk2).
These correspond to:
- sysclk: frequency of the CPU
- hclk: frequency of the AHB bus, core memory and DMA
- pclk1: frequency of the APB1 bus
- pclk2: frequency of the APB2 bus
Supported frequencies are (in MHz): 8, 16, 24, 30, 32, 36, 40, 42, 48,
If given any arguments then the function sets the frequency of the CPU,
and the busses if additional arguments are given. Frequencies are given in
Hz. Eg freq(120000000) sets sysclk (the CPU frequency) to 120MHz. Note that
not all values are supported and the largest supported frequency not greater
than the given value will be selected.
Supported sysclk frequencies are (in MHz): 8, 16, 24, 30, 32, 36, 40, 42, 48,
54, 56, 60, 64, 72, 84, 96, 108, 120, 144, 168.
The hclk, pclk1 and pclk2 frequencies are derived from the sysclk frequency
using a prescaler (divider). Supported prescalers for hclk are: 1, 2, 4, 8,
16, 64, 128, 256, 512. Supported prescalers for pclk1 and pclk2 are: 1, 2,
4, 8. A prescaler will be chosen to best match the requested frequency.
A sysclk frequency of
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
in boot.py, before the USB peripheral is started. Also note that sysclk
frequencies below 36MHz do not allow the USB to function correctly.
.. function:: wfi()