ChibiOS Free Embedded RTOS

Thanks Giovanni I will have to check that out. I have a BS in Electrical Engineering and an MS in Computer Engineering but I have always been better at hardware than software. Looking through the ChibiOS code has taught me some interesting tricks. Coding is so frustrating to me because I am good ...

Hi Giovanni,

I have been having a a great time looking through the ARMCMx port of ChibiOS to see how you implemented everything. It got me wondering "How did he know how to do all of this?". Are there any resources (e.g. books, websites, magazines) that have helped you in your design? I do not know ...

I believe you that this is the most complicated part!

So this is what I see from the code:

At the end of an interrupt PORT_IRQ_EPILOGUE() creates a space for an ISR stack frame (the "fake" frame) and makes sure the bit to indicate Thumb execution is set. It then checks to see another thread has ...

Hi everyone,

So I have spent the last few evenings really trying to learn how the ARM port of ChibiOS works. I am a bit hung up on the use of extctx. Here is my understanding of the two ctx structures:

extctx (External Context?): The are the registers a function is allowed to clobber. After a call ...

Hmmm, I am having a hard time find the EABI document. I have found the "Base Standard ABI" and "Base Platform ABI" and the "Procedure Call Standard for the Arm Architecture" I can't seem to find anything that talks about alignment sections in RAM other than the quote I posted in my first post. I ...

Hi all,

I was wondering if anyone could point me to the documents that discuss stack and section alignment?

I have been looking through the linker script for the STM32F4xx series and notices that several output sections are 16-byte aligned (e.g. startup : ALIGN(16) SUBALIGN(16)) while others are 4 ...

Muahaha! Thank goodness, I finally understand it.

Just to verify I commented out the "touching" of the registers and recompiled. The compiler still added those registers to the prologue. Thank you so much for walking me through how this all works. I have a much better grasp on it now.

Sam

Phew, I got my port up and working. It isn't really much more than extending the program counter and adding a few registers to extctx, but still it is working.

I hate to ask this but I have to: The ISR calls a function (port_switch) so why do we need to manually save the call-used registers (r18 ...

Thank you for your patience.

That makes sense. I need to really start thinking more about what the compiler expects in terms of call-saved and call-used registers. I keep thinking that I have to do it all, while in reality the compiler will do most of it.

Sam

Alright, that makes sense... but I should still save all of special "registers" in the ISR prologue right? That way when a task is switched back in these registers won't contain the garbage from a previous thread.

If that is true the problem I am facing is that the compiler saves some of these ...