Fast Interrupt (Fiq) - Texas Instruments UCD3138 Technical Reference Manual

Hardware Interrupts

14.2.2 Fast Interrupt (FIQ)

FIQ is similar to IRQ. The following are a few differences that may make FIQ faster:
• FIQ has higher priority than IRQ, therefore IRQ execution can be interrupted by FIQ, but FIQ execution
can not be interrupted by IRQ
• FIQ mode provides additional banked registers R8 to R14 that may be utilized to reduce the interrupt
response tim
Note that FIQ holds the last interrupt vector
immediately after the interrupt vector table, thus saving a branch instruction execution time.
14.3 Software Interrupt
Software interrupt is not an interrupt in the regular sense of a software routine that is getting called by an
external event. Software interrupt is initiated by the sequential execution of the software and by calling a
specific function. The call to a software interrupt function looks identical to a call to any other standard
function.
Declaration of a new function and its mapping to software interrupt is done through aliasing pragma.
#pragma SWI_ALIAS (erase_data_flash_segment, 0)
void erase_data_flash_segment(Uint8 segment);
The major functional difference between the two is that during a call to the software interrupt function the
ARM7 will switch to a privileged mode.
In this privileged mode the software will be able to enable/disable interrupts, manipulate Program and
Data flash content and more. None of these are accessible when ARM7 is in User mode.
Then the implementation of the function should be added in the relevant case inside the switch/case
expression in the body of software interrupt.
#pragma INTERRUPT(software_interrupt,SWI)
void software_interrupt(Uint32 arg1, Uint32 arg2, Uint32 arg3, Uint8 swi_number)
{ switch (swi_number)
{
case 0:
{
// Erase one segment of Data Flash
return;
}
case 1:
{
}
return;
}
}
456
ARM7TDMI-S MPUSS
(Table 14-5). So the FIQ service routine can be placed
Copyright © 2016, Texas Instruments Incorporated
SNIU028A – February 2016 – Revised April 2016
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