Texas Instruments TMS320C28 series Reference Manual page 119

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have to save the RB register.
; Repeat Block within a High-Priority Interrupt (Non-Interruptible)
;
; Interrupt:
ISR
BlockEnd
A low-priority interrupt is defined as an interrupt that allows itself to be interrupted. The
RB register must always be saved and restored in a low-priority interrupt. The RB
register must stored before interrupts are enabled. Likewise before restoring the RB
register interrupts must first be disabled.
; Repeat Block within a Low-Priority Interrupt (Interruptible)
;
; Interrupt:
POP RB
See also
PUSH RB
RPTB #RSIZE, loc16
SPRUEO2A – June 2007 – Revised August 2008
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; RAS = RA, RA = 0
...
PUSH RB ; Save RB register only if a RPTB block is used in the
...
...
RPTB #BlockEnd, #5 ; Execute the block 5+1 times
...
...
...
; End of block to be repeated
...
...
POP RB ; Restore RB register
...
IRET ; RA = RAS, RAS = 0
; RAS = RA, RA = 0
...
PUSH RB ; Always save RB register
...
CLRC INTM ; Enable interrupts only after saving RB
...
...
... ; ISR may or may not include a RPTB block
...
...
SETC INTM ; Disable interrupts before restoring RB
...
POP RB ; Always restore RB register
...
IRET ; RA = RAS, RAS = 0
Instructions
Instruction Set 119