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Hi Everyone, My code locks-up in an infinite loop by getting into the Illegal Opcode interrupt routine. Now the book says the way to get out of this is by popping/pulling the stack of the return address of the illegal opcode. I know I can do this by using the In-line assembly function " _opc( opcode ); " My question is what opcode should I use to pop the return address from the Illegal opcode instruction. I know it is a PULL instruction opcode, but how do I specify popping the return address which would be the last address placed on stack?? Regards, Musibau O. Alowonle Project Engineer - Electrical Ph: 763-540-1506 fax: 763-513-1710 e-mail: |
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Illegal opcode
Started by ●July 17, 2003
Reply by ●July 18, 20032003-07-18
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----- Original Message ----- From: Alowonle, Musibau <> To: <> Sent: Friday, July 18, 2003 1:01 AM Subject: [m68HC11] Illegal opcode > My code locks-up in an infinite loop by getting into the Illegal Opcode > interrupt routine. Now the book says the way to get out of this is by > popping/pulling the stack of the return address of the illegal opcode. I > know I can do this by using the In-line assembly function " opc( opcode > ); " > > My question is what opcode should I use to pop the return address from the > Illegal opcode instruction. I know it is a PULL instruction opcode, but how > do I specify popping the return address which would be the last address > placed on stack?? Illegal opcode exceptions are next to impossible to recover from. For one, you can't be sure the instruction causing the exception was the first one to execute out of order. For example, a huge sequence of valid opcodes could have executed right before the illegal opcode. Retrieving the address of the illegal opcode is useful not so much for recovery as for debugging or special purposes, meaning the addition of user-specified opcodes that are not part of the original instruction set and are taken care of inside the Illegal Opcode Handler. I would not trust to continue execution of a program that unexpected enters the Illegal Opcode Handler, without initiating some kind of reset. > Musibau O. Alowonle |
Reply by ●July 18, 20032003-07-18
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--- "Alowonle, Musibau" <> wrote: > Hi Everyone, > > My code locks-up in an infinite loop by getting into the Illegal Opcode > interrupt routine. Now the book says the way to get out of this is by > popping/pulling the stack of the return address of the illegal opcode. I > know I can do this by using the In-line assembly function " _opc( opcode > ); " > > My question is what opcode should I use to pop the return address from the > Illegal opcode instruction. I know it is a PULL instruction opcode, but how > do I specify popping the return address which would be the last address > placed on stack?? > > Regards, > Musibau O. Alowonle > Project Engineer - Electrical > Ph: 763-540-1506 > fax: 763-513-1710 > e-mail: Here is a routine I use to skip illegal op-codes. It will just step through a section of bad code until it reaches executable code. In most cases, though, you would want to signal your program or the operating system that you had this problem. This is the interupt handler for the IOT exception: HandleIOT tsx ; get stack pointer in X ldd 7,x ; get current program counter addd #1 ; point to next op-code std 7,x ; put new PC back on stack ; < here, signal your program that something bad happened > rti This routine will return to the location one byte after the illegal op-code. Regards, Jim Dodd Onset Computer Corp. __________________________________ |
