[ECOS] idle thread stack alignment problem

Nick Garnett nickg@ecoscentric.com
Sun Dec 21 23:16:00 GMT 2003

"Uwe Kindler" <uwe_kindler@web.de> writes:

> Hello,
> in order to debug the serial driver for the EDOSK platform, I created a
> simple application with one single thread. As soon, as the common serial
> eCos driver calls cyg_drv_cond_wait my application crashs. (At least it does
> not respond to GDB anymore).  If only one thread is present,
> cyg_drv_cond_wait causes a thread switch to the idle thread. When I create a
> second thread with an empty while loop my application runs well. So there
> must be a problem with the idle thread. After hours of debugging I found
> that the idle thread stack starts at an odd address. But for the H8S
> architecture its is required that the SP is always even (word or longword
> size operands when using SP). When I changed the declaration of the idle
> thread stack in this way:
> static short
> ZE/2];
> everything works fine without a crash.
> Is there a way to change the alignment of the thread stack without changing
> the thread.cxx sourcecode? I did not found any other way then the one
> described above.

The usual approach is to not worry about the lower limit of the stack,
but to align the SP in HAL_THREAD_INIT_CONTEXT() when the thread is
intialized. The size of HAL_SavedRegisters should also be set such
that when it is pushed during exception/interrupt processing the
stack alignment is preserved.

Nick Garnett                    eCos Kernel Architect
http://www.ecoscentric.com      The eCos and RedBoot experts

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