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RTI: Difference between revisions
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'''RTI''' (ReTurn from Interrupt) is a 65x instruction used to return control from an [[interrupt handler]]. It does this by first pulling the [[status flags]] off of the [[stack]] and then the [[program counter]] too. | '''RTI''' (ReTurn from Interrupt) is a 65x instruction used to return control from an [[interrupt handler]]. It does this by first pulling the [[status flags]] off of the [[stack]] and then the [[program counter]] too. In native mode, 4 bytes are pulled. In emulation mode, 3 bytes are pulled. | ||
==== Syntax ==== | ==== Syntax ==== | ||
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* Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#RTI | * Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#RTI | ||
* Clark, Bruce. http://www.6502.org/tutorials/65c816opcodes.html#6.3.2 | * Clark, Bruce. http://www.6502.org/tutorials/65c816opcodes.html#6.3.2 | ||
* lbid, APPENDIX: EMULATION MODE, http://www.6502.org/tutorials/65c816opcodes.html#APPENDIX: | |||
[[Category:ASM]] | [[Category:ASM]] | ||
Revision as of 23:03, 31 July 2024
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | Speed | ||||
| Stack (RTI) | 40 | 1 byte | 7 cycles* | ||||
| Flags Affected | ||||||||
|---|---|---|---|---|---|---|---|---|
| N | V | M | X | D | I | Z | C | |
| 65c816 native mode | N | V | M | X | D | I | Z | C |
| 6502 emulation mode | N | V | . | . | D | I | Z | C |
RTI (ReTurn from Interrupt) is a 65x instruction used to return control from an interrupt handler. It does this by first pulling the status flags off of the stack and then the program counter too. In native mode, 4 bytes are pulled. In emulation mode, 3 bytes are pulled.
Syntax
RTI
Pitfalls
- RTI should only be run when the e flag is in the same state as when the interrupt fired
- RTI cannot even tell whether the interrupt actually occurred or not
- RTI does not increment the program counter after pulling it like RTS and RTL do
Cycle Skipped
RTI takes one fewer cycle in emulation mode as the program bank register doesn't need to be pulled from the stack.
See Also
External Links
- Eyes & Lichty page 492, on RTI: https://archive.org/details/0893037893ProgrammingThe65816/page/492
- Labiak page 176 on RTI: https://archive.org/details/Programming_the_65816/page/n186
- MCS6500 Manual page 132 on RTI: https://archive.org/details/mos_microcomputers_programming_manual/page/n152
- Carr page 270 on RTI: https://archive.org/details/6502UsersManual/page/n283
- Leventhal page 3-89 on RTI: https://archive.org/details/6502-assembly-language-programming/page/n138
- snes9x implementation of RTI: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L3272
- undisbeliever on RTI: https://undisbeliever.net/snesdev/65816-opcodes.html#rti-return-from-interrupt
- Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#RTI
- Clark, Bruce. http://www.6502.org/tutorials/65c816opcodes.html#6.3.2
- lbid, APPENDIX: EMULATION MODE, http://www.6502.org/tutorials/65c816opcodes.html#APPENDIX: