>For some reason, my interrupts have stopped working.
>
>I think it's something to do with Program memory bank 1 - my code's
>gotten to the stage where I've had to start dumping routines into the
>second bank - calling them from the first bank.
>
>When I call a routine in bank 1 and loop there waiting for an interrupt
>driven timer to time out, it never does - it just goes round and round
>the loop.  The SCI interrupt and the keyboard interrupt don't work
>either.
snip
>I'm saving context ok in the interrupt (W,Status,FSR and PCLATH) - and
>in fact the interrupt code never seems to get run at all (I put a port
>flag in to check and it never gets set)

One idea: do you do something like:

        org 04
        goto interrupt

If so, the goto is the problem... pclath is pointing to ROM Pg1 and you jump
to somewhere not intended.  The way that I handle it is to put all the
context saving stuff right at the start as follows:

    ORG         00H
    goto        COLDBOOT

    ORG         04H
;save W, STATUS, PCLATH, FSR
    movwf       W_SAVE          ;save w (could be on either ram page)
    movfw       STATUS          ;status register now trashed
    clrf        STATUS          ;ensure ram page 0
    movwf       S_SAVE          ;good copy of status register in Page 0
    movfw       PCLATH          ;remember to also save FSR if necessary
    movwf       P_SAVE
    clrf        PCLATH          ;ensure ROM page 0

;which interrupt?  Parse interrupt flags here to reduce jumps (and time)
    btfsc       INTF            ;RB0 interrupt?
      goto      RB0_ISR
    btfss       T0IF            ;timer 0 interrupt?
      goto      TMR0_ISR
    goto        INT_END         ;this shouldn't happen!


;jump tables live here


;interrupt routines live here