msp430: twi: move interrupt handler for USCI_Bx to twi.c

[alfh]

For the USCI module, it shares interrupt vector for
USCI_Ax and USCI_Bx, so the interrupt routine should still
be in usci_isr_handler.

But for USCI_B0 and USCI_B1, the interrupt handler can be
moved to twi.c. This is exactly the same way it is done
for the EUSCI_Bx module, it already has the interrupt
handler in twi.c

[alfh]

@spirilis I am a bit unsure about the "stay_asleep" code.
Does it seem correct to define

#if defined(MSP430_HAS_USCI_B0) || defined(MSP430_HAS_USCI_B1) || defined(MSP430_HAS_EUSCI_B0)
static boolean still_asleep; // Used to validate whether a user ISR has issued wakeup() inside LPM3/LPM4 sleep modes.
#endif

in twi.c ?

Also, I do not understand why you have not added the "stay_asleep" code blocks in the interrupt handler for EUSCI_B0, in twi.c.
And likewise for the USI interrupt handler in twi.c.
Any comments ?

Regards
Alf

[spirilis]

I don't have the code in front of me, but with stay_asleep code, ask yourself if there's a potential to run a user-provided callback function in the ISR. If so, the stay_asleep code should be there.

I believe I2C slave callback functions may be a reason for this.