CMSIS Dynamic selection of IRC vs XTAL?

[lpcware]

Content originally posted in LPCWare by MX21 on Wed Dec 10 15:00:39 MST 2014
I'm using LPCXpresso Code Red with CMSIS for my project.  I have an existing board with LPC1227 that uses the IRC for clock.  I have another new board that uses an external crystal (12MHz). 

From what I can find, the clock source is setup in system_LPC122x.c at compile time with a bunch of macros.  This is the common CMSIS library referenced from multiple projects.  If I edit system_LPC122x.c it will change the clock for all of my projects.

I'd like to have my code support both of my boards, by reading a GPIO pin at startup to determine which board it is, then configure the clock to use the external crystal if it is the newer board.

Is there a way to do this through CMSIS?  Or do I just need to program registers directly (thus somewhat defeating the hardware abstraction purpose of CMSIS)?

Thanks

[lpcware]

Content originally posted in LPCWare by MX21 on Wed Feb 25 12:09:41 MST 2015
I have it working by reading IO pins after it gets into main, then using the LPC_SYSCON registers to setup the clock again using the crystal.  I just expected that, since CMSIS is designed to abstract the hardware, there would be a function to do this.

[lpcware]

Content originally posted in LPCWare by 1234567890 on Wed Feb 25 11:23:56 MST 2015
Is it really neccessary to change the clock source at startup?
By the way: What is your definition of startup?

Generally you can edit the provided startup files. You have the source code to do so. But it should/could start at special point. Generally the chips start with the IRC as clock source because it is a known frequency. This is needed to initialise things.

Without editing the startup files: Isn't it early enough for you to change the clock source at the beginning of main? Read your pin and use the provided functions (LPCOpen, CMSIS, registers) to change the clock source.

[lpcware]

Content originally posted in LPCWare by MX21 on Tue Feb 24 22:56:34 MST 2015
Still no CMSIS means to set the clock at runtime?

[lpcware]

Content originally posted in LPCWare by MX21 on Fri Dec 12 15:26:04 MST 2014
So, I guess there is no run-time function in CMSIS to change the clock source?

Do I just write the registers directly, then call SystemCoreClockUpdate?

[lpcware]

Content originally posted in LPCWare by MX21 on Wed Dec 10 15:12:53 MST 2014

---

Quote: whitecoe
Just take a copy of the system_LPC122x.c and put it into your application project. You can then edit the version within the application project without affecting any other projects in your workspace that use the version from the CMSIS library project. ie the local copy will get used in preference to the one from the library project.

HTH!

---

Thanks for the quick response.  That will help for most of my projects, but in this case, it's the same code loaded on two board versions, one with crystal, one without.  So I need to select it at runtime.

[lpcware]

Content originally posted in LPCWare by whitecoe on Wed Dec 10 15:05:50 MST 2014
Just take a copy of the system_LPC122x.c and put it into your application project. You can then edit the version within the application project without affecting any other projects in your workspace that use the version from the CMSIS library project. ie the local copy will get used in preference to the one from the library project.

HTH!