Illegal - Motorola DSP56800 Manual

ILLEGAL

Operation:
Begin illegal instruction exception routine
Description: Normal instruction execution is suspended and illegal instruction exception processing is initiated. The
interrupt priority level bits (I1 and I0) are set to 11 in the status register. The purpose of the illegal in-
terrupt is to force the DSP into an illegal instruction exception for test purposes. Executing an ILLE-
GAL instruction is a fatal error; the exception routine should indicate this condition and cause the sys-
tem to be restarted.
If the ILLEGAL instruction is in a DO loop at the LA and the instruction at the LA-1 is being inter-
rupted, then LC will be decremented twice due to the same mechanism that causes LC to be decrement-
ed twice if JSR, REP,... are located at the LA.
Since REP is uninterruptible, repeating an ILLEGAL instruction results in the interrupt not being taken
until after completion of the REP. After servicing the interrupt, program control will return to the ad-
dress of the second word following the ILLEGAL instruction. Of course, the ILLEGAL interrupt ser-
vice routine should abort further processing, and the processor should be reinitialized.
Usage:
The ILLEGAL instruction provides a means for testing the interrupt service routine executed upon dis-
covering an illegal instruction. This allows a user to verify that the interrupt service routine can cor-
rectly recover from an illegal instruction and restart the application. The ILLEGAL instruction is not
used in normal programming.
Example:
ILLEGAL
Explanation of Example: See the previous description.
Condition Codes Affected:
The condition codes are not affected by this instruction.
Instruction Fields:
Operation
ILLEGAL
Timing:
4 oscillator clock cycles
Memory: 1 program word
Illegal Instruction Interrupt
Assembler Syntax:
ILLEGAL
Operands C
4
Instruction Set Details
(no parallel move)
W
1 Execute the illegal instruction exception. This
instruction is made available so that code may be
written to test and verify interrupt handlers for illegal
instructions.
ILLEGAL
Comments
A-83