[Avrora] MSP430 / TelosB support for Avrora

Urs Hunkeler urs.hunkeler at epfl.ch
Tue Jan 18 11:40:07 PST 2011


Hi Roy,

Thanks for your answer! Yes, I looked into the slau049f.pdf document, 
that's how I figured that the carry bit's meaning for subtractions must 
be reversed. I hadn't seen the note about the borrow, though, and even 
if I had I wouldn't have understood it. I'm not familiar with "borrow", 
but I'll look into it. I'll have to figure out whether additions with 
negative numbers are affected...

I haven't really done much with the instruction set (other than 
debugging), it was all already there. My contributions are mostly with 
the internal devices (timer, clock module, watchdog, I/O pins) and MCU 
functionality beyond simple instruction processing (interrupt handling, 
sleep mode).

Cheers,
Urs


On 1/18/11 7:57 PM, Roy Shea wrote:
> Hello Urs,
>
> Great job getting the simulation for blink up and running on the MSP430!
>
>> I think the MSP430 handles the carry bit differently from other
>> architectures (at least for subtraction). I am still not sure how exactly it
>> works, but by inverting the meaning for subtractions (sub, subc and cmp
>> instructions) I got the simulation of the TinyOS Blink application to work.
> With regards to the carry bit, take a look at the instruction summary
> provided in the user guide for the subtraction operations:
>
> http://focus.ti.com/lit/ug/slau049f/slau049f.pdf
>
> There's a note describing the fact that the borrow used to set the carry
> flag is treated as a .NOT so that:
>
> Borrow yes ->  Carry 0
> Borrow no ->  Carry 1
>
> Does that clear things up?
>
> Again, great job getting the MSP430 instruction set further along.
>
> Peace,
> -Roy
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