TI MSP430 Notes

Every platform beeing it hardware of software has some oddities you should be aware of for maximum coding pleasure. The advises below are based on our experience we gathered while making the DMX43 Project.

CPU

If you mov some byte values into a register the upper byte of the register will be cleared. This differs from x86 CPUs!. Example:

mov   0x1122, R15
mov.b 0xff,   R15

R15 now contains the value 0x00FF and not 0x11FF.

Oscilators

The MSP430 is very afraid of loosing external oscilator/clock sources. If anything suspicious happens with external clocks the MSP will fall back to its internal clock generators. Upon fall back an osc fail interrupt is triggered. This osc failure is so sensitive that it triggers if you apply an oscilloscope to the clock source and even if you touch the contacts with your finger!

If an osc fail interrupt is triggered you should simply reset the external clock source and the system. A nice solution is the following program layout:

; startup code
startup:
call    #osc_setup
...

; subroutine to set up external clocks
osc_setup:
bis.b	#XTS,	&BCSCTL1 ; select XT1
...
ret

; interrupt routine for osc failure, flash violation and nmi
osc_failure_interrupt:
dint
bit.b	#OFIFG,	&IFG1
jz	next1
call	#osc_setup
jmp     return
next1:  bit.b   #NMIIE, &IFG1
jz      next2
...
jmp     return
next2:  bit.b   #ACCVIE,&IFG1
jz      return
...
return:	eint
reti

BSL Bootstrap Loader

Some revisions of the MSP430 have bugs in their internal boot strap loader. BSL version < 1.10 have to be patched to provide write access to addresses > 0x8000. You have to apply this patch every time you issued a write operation into either the ram or flash area of the MSP or subsequent writes will fail.

Links

GCC and binutils for MSP430. They also have a Python BSL.

ASL assembler a powerfull macro assembler for every important processor on earth.

bslsh BSL frontend for un*x OS.

MSP430F149 test board you could use, if you don't want to solder those little smd devices for yourself.

Pong