[PATCH] Fix exception handler for supporting FPU

[sudarshan.rajagopalan]

On 2015-08-28 11:30, Daniel Gutson wrote:
> On Fri, Aug 28, 2015 at 12:20 PM, Gedare Bloom <gedare at gwu.edu> wrote:
>> Could you please open a ticket on our trac to describe the problem
>> this fixes, and add "closes #xxxx." to your patch commit message?

Hi Gedare, Sure will do!

> 
> Additionally, please clarify which architecture this applies to. I
> suspect this is for cortex-m4.
> In any case, please clarify which architectures you tested on. We can
> analyze and test cortex-m3 if you don't have one.

Daniel, I've tested it on Cortex-M4 but this patch should also apply to 
Cortex-M3 or all ARMv7M based processor (including M7). But please feel 
free to test it on Cortex-M3 since I don't have it with me now.

Am also attaching the links to ARM Cortex-M3, M4 and M7 Exception entry 
and return referenece documents for a quick reference, where the table 
gives all the possible exception error codes returned and which SP to 
pick depending on the error code. The only tricky part would be error 
code: 0xFFFFFFE1. But the asm "tst.w lr, #4" with lr=0xFFFFFFE1 will 
result into zero and will set the Zero flag, which will make the ITT EQ 
block execute, which will choose MSP, which it should for the return 
code 0xFFFFFFE1 (or even 0xFFFFFFF1) in all M3, M4 and M7. But please 
feel free to test it on real M3 an M7 processor. I have tested it by 
manually giving all the return error codes for M3 and M7 to LR and and 
it chooses the right SP value.

ARM Reference Docs - Exception Entry and Return:
C-3: 
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0552a/Babefdjc.html
C-4: 
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0553a/Babefdjc.html
C-7: 
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0646a/Babefdjc.html

Thanks and Regards,
Sudarshan

> 
>> 
>> Thanks,
>> Gedare
>> 
>> On Thu, Aug 27, 2015 at 4:33 PM, sudarshan.rajagopalan
>> <sudarshan.rajagopalan at vecna.com> wrote:
>>> Patch attached here for ARMv7M Exception Handler. Looks like git 
>>> send-email
>>> didn't deliver the mail. Something is not quite right with our mail 
>>> server
>>> here. Avoid this email if patch delivered through git.
>>> 
>>> Thanks and Regards,
>>> 
>>> Sudarshan
>>> 
>>> 
>>> 
>>> 
>>> _______________________________________________
>>> devel mailing list
>>> devel at rtems.org
>>> http://lists.rtems.org/mailman/listinfo/devel
>> _______________________________________________
>> devel mailing list
>> devel at rtems.org
>> http://lists.rtems.org/mailman/listinfo/devel