dsp56800 Freescale Semiconductor, Inc, dsp56800 Datasheet - Page 309

• Manufacturer Part Number: dsp56800
• Description: 16-bit Digital Signal Controllers
• Manufacturer: Freescale Semiconductor, Inc

ILLEGAL
Operation:
Begin illegal instruction exception routine
Description: Normal instruction execution is suspended and illegal instruction exception processing is initiated. The
Usage:
Example:
Explanation of Example: See the previous description.
Condition Codes Affected:
Instruction Fields:
Timing:
Memory:
Freescale Semiconductor
Operation
ILLEGAL
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 DSC 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 not interruptible, repeating an ILLEGAL instruction results in the interrupt not being tak-
en until after completion of the REP. After servicing the interrupt, program control will return to the
address of the second word following the ILLEGAL instruction. Of course, the ILLEGAL interrupt
service routine should abort further processing, and the processor should be re-initialized.
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.
ILLEGAL
The condition codes are not affected by this instruction.
4 oscillator clock cycles
1 program word
Operands
Illegal Instruction Interrupt
Instruction Set Details
C
4
Assembler Syntax:
ILLEGAL
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.
Comments
ILLEGAL
A-79