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COP: Difference between revisions
From SnesLab
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* Signature bytes of 80h to FFh are reserved for future microprocessors by the [https://www.westerndesigncenter.com/ Western Design Center]<sup>[3]</sup> | * Signature bytes of 80h to FFh are reserved for future microprocessors by the [https://www.westerndesigncenter.com/ Western Design Center]<sup>[3]</sup> | ||
The state of the [[interrupt disable flag]] has no effect on the behavior of COP. | The state of the [[interrupt disable flag]] has no effect on the behavior of COP although it will be set after COP runs. | ||
COP triggers a software interrupt and control is routed to the COP handler, whose address is stored in the COP vector at $FFF4. COP could be used to communicate with | COP triggers a software interrupt and control is routed to the COP handler, whose address is stored in the COP vector at $FFF4. Some examples of the kinds of microprocessors COP could be used to communicate with include: | ||
* floating point | |||
* graphics | |||
The [[PBR]] is cleared, but in native mode its previous value is pushed to the [[stack]]. | The [[PBR]] is cleared, but in native mode its previous value is pushed to the [[stack]]. | ||
Revision as of 19:53, 9 August 2024
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | Speed | ||||
| Stack (Interrupt) | 02 | 2 bytes | 8 cycles* | ||||
| Flags Affected | ||||||||
|---|---|---|---|---|---|---|---|---|
| N | V | M | X | D | I | Z | C | |
| . | . | . | . | 0 | 1 | . | . | |
COP (Co-Processor) is a 65c816 instruction designed to run a co-processor command. The byte following the opcode is called the signature byte and is required by assemblers:
- Signature bytes of 00h to 7Fh can be programmer-defined
- Signature bytes of 80h to FFh are reserved for future microprocessors by the Western Design Center[3]
The state of the interrupt disable flag has no effect on the behavior of COP although it will be set after COP runs.
COP triggers a software interrupt and control is routed to the COP handler, whose address is stored in the COP vector at $FFF4. Some examples of the kinds of microprocessors COP could be used to communicate with include:
- floating point
- graphics
The PBR is cleared, but in native mode its previous value is pushed to the stack.
Syntax
COP sig
Cycle Skipped
- COP takes one fewer cycle in emulation mode as it doesn't need to push the program counter bank register to the stack.
See Also
External Links
- Eyes & Lichty, page 447 on COP
- Labiak, page 135 on COP
- section 7.15 of 65c816 datasheet
- snes9x implementation of COP: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L2738
- https://ersanio.gitbook.io/assembly-for-the-snes/deep-dives/misc
- https://undisbeliever.net/snesdev/65816-opcodes.html#software-interrupts