Suggestion: Make PLLM configurable

[dojyorin]

Suggestion

Do you I think good idea to make PLLM configurable from Arduino IDE menu?

This allows clock source to be flexibly configured.

For example, my recent favorite "Nucleo-H563ZI" board has HSE selected as default clock source.

Among them, you can use 8 MHz ST-LINK MCO (default), 25 MHz on-board crystal, or you can prepare and connect your own favorite crystal.

I want to take advantage of clock source flexibility that board provides.

But I don't want things to get too complicated.

The key part of this suggestion, fix PLL input frequency to 1 MHz by set PLLM to same value as HSE input frequency (MHz).

The PLL output frequency is PLLN value (MHz), and even if crystal is changed,　frequency ultimately supplied to　component can be fixed.

Implementation Example

Note! This is just conceptual code, so there may be mistakes.

boards.txt

menu.pllm=PLLM Custom Divider
Nucleo_144.menu.pllm.default=Default
Nucleo_144.menu.pllm.default.build.flags.pllm=
Nucleo_144.menu.pllm.div1=Div 1
Nucleo_144.menu.pllm.div1.build.flags.pllm=-DCUSTOM_PLLM=1
Nucleo_144.menu.pllm.div2=Div 2
Nucleo_144.menu.pllm.div2.build.flags.pllm=-DCUSTOM_PLLM=2
Nucleo_144.menu.pllm.div3=Div 3
Nucleo_144.menu.pllm.div3.build.flags.pllm=-DCUSTOM_PLLM=3
Nucleo_144.menu.pllm.div4=Div 4
Nucleo_144.menu.pllm.div4.build.flags.pllm=-DCUSTOM_PLLM=4
Nucleo_144.menu.pllm.div5=Div 5
Nucleo_144.menu.pllm.div5.build.flags.pllm=-DCUSTOM_PLLM=5
Nucleo_144.menu.pllm.div6=Div 6
Nucleo_144.menu.pllm.div6.build.flags.pllm=-DCUSTOM_PLLM=6
Nucleo_144.menu.pllm.div7=Div 7
Nucleo_144.menu.pllm.div7.build.flags.pllm=-DCUSTOM_PLLM=7
Nucleo_144.menu.pllm.div8=Div 8
Nucleo_144.menu.pllm.div8.build.flags.pllm=-DCUSTOM_PLLM=8
Nucleo_144.menu.pllm.div9=Div 9
Nucleo_144.menu.pllm.div9.build.flags.pllm=-DCUSTOM_PLLM=9
Nucleo_144.menu.pllm.div10=Div 10
Nucleo_144.menu.pllm.div10.build.flags.pllm=-DCUSTOM_PLLM=10
Nucleo_144.menu.pllm.div11=Div 11
Nucleo_144.menu.pllm.div11.build.flags.pllm=-DCUSTOM_PLLM=11
Nucleo_144.menu.pllm.div12=Div 12
Nucleo_144.menu.pllm.div12.build.flags.pllm=-DCUSTOM_PLLM=12
Nucleo_144.menu.pllm.div13=Div 13
Nucleo_144.menu.pllm.div13.build.flags.pllm=-DCUSTOM_PLLM=13
Nucleo_144.menu.pllm.div14=Div 14
Nucleo_144.menu.pllm.div14.build.flags.pllm=-DCUSTOM_PLLM=14
Nucleo_144.menu.pllm.div15=Div 15
Nucleo_144.menu.pllm.div15.build.flags.pllm=-DCUSTOM_PLLM=15
Nucleo_144.menu.pllm.div16=Div 16
Nucleo_144.menu.pllm.div16.build.flags.pllm=-DCUSTOM_PLLM=16
Nucleo_144.menu.pllm.div17=Div 17
Nucleo_144.menu.pllm.div17.build.flags.pllm=-DCUSTOM_PLLM=17
Nucleo_144.menu.pllm.div18=Div 18
Nucleo_144.menu.pllm.div18.build.flags.pllm=-DCUSTOM_PLLM=18
Nucleo_144.menu.pllm.div19=Div 19
Nucleo_144.menu.pllm.div19.build.flags.pllm=-DCUSTOM_PLLM=19
Nucleo_144.menu.pllm.div20=Div 20
Nucleo_144.menu.pllm.div20.build.flags.pllm=-DCUSTOM_PLLM=20
Nucleo_144.menu.pllm.div21=Div 21
Nucleo_144.menu.pllm.div21.build.flags.pllm=-DCUSTOM_PLLM=21
Nucleo_144.menu.pllm.div22=Div 22
Nucleo_144.menu.pllm.div22.build.flags.pllm=-DCUSTOM_PLLM=22
Nucleo_144.menu.pllm.div23=Div 23
Nucleo_144.menu.pllm.div23.build.flags.pllm=-DCUSTOM_PLLM=23
Nucleo_144.menu.pllm.div24=Div 24
Nucleo_144.menu.pllm.div24.build.flags.pllm=-DCUSTOM_PLLM=24
Nucleo_144.menu.pllm.div25=Div 25
Nucleo_144.menu.pllm.div25.build.flags.pllm=-DCUSTOM_PLLM=25
Nucleo_144.menu.pllm.div26=Div 26
Nucleo_144.menu.pllm.div26.build.flags.pllm=-DCUSTOM_PLLM=26
Nucleo_144.menu.pllm.div27=Div 27
Nucleo_144.menu.pllm.div27.build.flags.pllm=-DCUSTOM_PLLM=27
Nucleo_144.menu.pllm.div28=Div 28
Nucleo_144.menu.pllm.div28.build.flags.pllm=-DCUSTOM_PLLM=28
Nucleo_144.menu.pllm.div29=Div 29
Nucleo_144.menu.pllm.div29.build.flags.pllm=-DCUSTOM_PLLM=29
Nucleo_144.menu.pllm.div30=Div 30
Nucleo_144.menu.pllm.div30.build.flags.pllm=-DCUSTOM_PLLM=30
Nucleo_144.menu.pllm.div31=Div 31
Nucleo_144.menu.pllm.div31.build.flags.pllm=-DCUSTOM_PLLM=31
Nucleo_144.menu.pllm.div32=Div 32
Nucleo_144.menu.pllm.div32.build.flags.pllm=-DCUSTOM_PLLM=32

platform.txt

compiler.c.flags={compiler.extra_flags} -c {build.flags.optimize} {build.flags.debug} {build.flags.pllm}

variant_NUCLEO-H563ZI.cpp

// Default HSE input freq is 8 MHz from ST-LINK
// Generate reference 1 MHz by dividing by same value as HSE frequency.
#ifdef CUSTOM_PLLM
  RCC_OscInitStruct.PLL.PLLM = CUSTOM_PLLM;
#else
  RCC_OscInitStruct.PLL.PLLM = 8;
#endif

RCC_OscInitStruct.PLL.PLLN = 250;
RCC_OscInitStruct.PLL.PLLP = 1;
RCC_OscInitStruct.PLL.PLLQ = 1;
RCC_OscInitStruct.PLL.PLLR = 1;

[dojyorin]

I've researched some MCUs since then and it seems that this suggestion was wrong.

At least in H5 if PLL input frequency is less than 2MHz PLL multiplier cannot be higher than 420 and PLLP must be at least DIV2 or higher so it could not reach rated 250MHz.

It maybe compatible with other MCUs but in STM32duino Nucleo boards are grouped into 32/64/144 variants so only boards equipped with specific MCU among them I thought it would be difficult to increase PLLM options.

[fpistm]

Sorry forgot to answer.
Honestly adding new menu is not a good idea. It is hard to support and it is very limited by Arduino IDE.
This would bring more confusion than help.
Nevertheless, You can define a boards.local.txt for your own need: https://arduino.github.io/arduino-cli/0.34/platform-specification/#boardslocaltxt