Ensure that stack pointer is correctly aligned during thread creation on MSP430

[rousselk]

I encountered an error on my beta Z1 port during enter_ISR(), because of an odd (mis-aligned SP register).

When debugging, I noticed the lack of a correct check for misalignment during thread creation on MSP430. This is my proposed correction.

[rousselk]

Maybe would it be a good idea to ensure correct alignment of stack in thread_create() function in core/thread.c, just like the TCB is already aligned on 32-bit boundary in the very same function?

[Kijewski]

Doesn't the decreasing need to come before the setting, like it was before? In the start stk points to the byte after the end of the stack, doesn't it?

[rousselk]

Aah, indeed. My bad.
I'm correcting that right away.

[rousselk]

Done. SP should now have the right value after thread creation on MSP430 (it surely seems to be so under Cooja).

[Kijewski]

I have no means to test this, but the change looks good. 👍

[OlegHahm]

Will test ASAP, but agree with @Kijewski: looks good.

Concerning the alignment check in thread.c. @LudwigOrtmann and I thought about this some time ago, but apparently failed to create a ticket.

[rousselk]

Well, these fixes (along with PR #882, and #101 in projects repository) allow me to pass the test_cc2420 test application on Z1.

[OlegHahm]

Tested on MSB-430h. ACK and go.