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71 lines
2.1 KiB
Markdown
71 lines
2.1 KiB
Markdown
The Description-Based Direct Memory Access (DBDMA) relies on memory-based descriptions, minimizing CPU interrupts.
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| Channel | Number |
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|:-----------------:|:------:|
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| SCSI0 | 0x0 |
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| FLOPPY | 0x1 |
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| ETHERNET TRANSMIT | 0x2 |
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| ETHERNET RECIEVE | 0x3 |
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| SCC TRANSMIT A | 0x4 |
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| SCC RECIEVE A | 0x5 |
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| SCC TRANSMIT B | 0x6 |
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| SCC RECIEVE B | 0x7 |
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| AUDIO OUT | 0x8 |
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| AUDIO IN | 0x9 |
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| SCSI1 | 0xA |
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What's notable about the registers is that they are in little-endian format, thus Mac OS uses the stwbrx and lwbrx instructions to store values.
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| Register | Offset |
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|:-----------------:|:------:|
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| ChannelControl | 0x00 |
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| ChannelStatus | 0x04 |
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| CommandPtrHi | 0x08 |
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| CommandPtrLo | 0x0C |
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| InterruptSelect | 0x10 |
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| BranchSelect | 0x14 |
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| WaitSelect | 0x18 |
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| TransferMode | 0x1C |
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| Data2PtrHi | 0x20 |
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| Data2PtrLo | 0x24 |
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| BranchPtrHi | 0x2C |
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| BranchPtrLo | 0x30 |
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| Command | Value |
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|:-----------------:|:------:|
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| OUTPUT_MORE | 0x0 |
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| OUTPUT_LAST | 0x1 |
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| INPUT_MORE | 0x2 |
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| INPUT_LAST | 0x3 |
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| STORE_QUAD | 0x4 |
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| LOAD_QUAD | 0x5 |
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| NOP | 0x6 |
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| STOP | 0x7 |
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| Key Name | Value |
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|:-----------------:|:------:|
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| KEY_STREAM0 | 0x0 |
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| KEY_STREAM1 | 0x1 |
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| KEY_STREAM2 | 0x2 |
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| KEY_STREAM3 | 0x3 |
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| KEY_REGS | 0x5 |
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| KEY_SYSTEM | 0x6 |
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| KEY_DEVICE | 0x7 |
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## Control Register
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| Value | Offset |
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|:-----------:|:------:|
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| Branch | 0x100 |
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| Active | 0x400 |
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| Dead | 0x800 |
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| Wake | 0x1000 |
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| Flush | 0x2000 |
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| Pause | 0x4000 |
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| Run | 0x8000 |
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## References
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* https://stuff.mit.edu/afs/sipb/contrib/doc/specs/protocol/chrp/chrp_io.pdf
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* https://stuff.mit.edu/afs/sipb/contrib/doc/specs/protocol/chrp/chrp_hrpa.pdf |