IP2022 User’s Manual—System Architecture www.ubicom.com 41 2.5.2 Global Interrupt Enable Bit The GIE bit serves two purposes: • Preventing an interrupt in a critical section of mainline code • Supporting nested interrupts The GIE bit is automatically cleared when an interrupt occurs, to
disable  interrupts  while  the  ISR  is  executing.  The  GIE  bit  is
automatically set by the reti instruction to re-enable interrupts
when the ISR returns. To re-enable interrupts during ISR execution, the ISR code must
first clear the source of the first interrupt. It may also be desirable Table 2-2  GIE Bit Handling
Event Effect Enter ISR (interrupt) GIE bit is cleared Exit ISR (reti instruction) GIE bit is set setb xcfg,7 instruction (inside ISR) Enable interrupts for
nested interrupt
support clrb xcfg,7 instruction (inside ISR) Nothing, the GIE bit
is already clear setb xcfg,7 instruction (mainline code) Enable interrupts clrb xcfg,7 instruction (mainline code) Disable interrupts