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83 lines
3.7 KiB
Markdown
83 lines
3.7 KiB
Markdown
# ROM
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The Old World ROM is always 4 megabytes (MB). The first three MB are reserved for the 68k code, while the last MB is for the PowerPC boot-up code.
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# Serial
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For serial, it replicates the functionality of a Zilog ESCC. There are two different ports - one located at (MacIOBase) + 0x13000 for the printer, and the other at (MacIOBase) + 0x13020 for the modem.
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# DBDMA
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The Description-Based Direct Memory Access 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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# NCR 53C94
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The NCR 53C94 is the SCSI controller.
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# Register Map
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| Offset | Read functionality |Write functionality |
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|:------:|:------------------------:|:-------------------------:|
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| 0x0 | Transfer counter LSB | Transfer counter LSB |
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| 0x1 | Transfer counter MSB | Transfer counter MSB |
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| 0x2 | FIFO | FIFO |
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| 0x3 | Command | Command |
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| 0x4 | Status | Destination Bus ID |
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| 0x5 | Interrupt | Select/reselect timeout |
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| 0x6 | Sequence step | Synch period |
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| 0x7 | FIFO flags/sequence step | Synch offset |
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| 0x8 | Configuration 1 | Configuration 1 |
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| 0x9 | | Clock conversion factor |
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| 0xA | | Test mode |
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| 0xB | Configuration 2 | Configuration 2 |
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| 0xC | Configuration 3 | Configuration 3 |
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| 0xF | | Reserve FIFO Byte (Cfg 2) |
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# SWIM 3
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The SWIM 3 (Sanders-Wozniak integrated machine 3) is the floppy drive disk controller. As can be inferred by the name, the SWIM III chip is the improvement of a combination of floppy disk driver designs by Steve Wozniak (who worked on his own floppy drive controller for early Apple computers) and Wendell B. Sander (who worked on an MFM-compatible IBM floppy drive controller).
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The SWIM chip is resided on the logic board physically and is located at IOBase + 0x15000 in the device tree. It sits between the I/O controller and the floppy disk connector. Its function is to translate the I/O commands to specialized signals to drive the floppy disk drive, i.e. disk spinning speed, head position, phase sync, etc.
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Unlike its predecessor, it allowed some DMA capability.
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The floppy drives themselves were provided by Sony.
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Some New World Macs do have a SWIM 3 driver present, but this normally goes unused due to no floppy drive being connected.
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# NVRAM
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Mac OS relies on 8 KB of NVRAM at minimum to run properly. It's usually found at IOBase (ex.: 0xF3000000 for Power Mac G3 Beige) + 0x60000.
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# PMU
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| Command Name | Number | Functionality |
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|:----------------:|:------:|:----------------------------:|
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| PMUpMgrADB | 0x20 | Send ADB command |
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| PMUpMgrADBoff | 0x21 |
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| PMUxPramWrite | 0x32 |
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| PMUtimeRead | 0x38 |
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| PMUxPramRead | 0x3A |
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| PMUmaskInts | 0x70 |
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| PMUreadINT | 0x78 |
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| PMUPmgrPWRoff | 0x7E |
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| PMUResetCPU | 0xD0 |
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# Miscellaneous
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The Power Mac G3 Beige has an additional register at 0xFF000004, which is dubbed varyingly as the "cpu-id" (by Open Firmware), the ""systemReg" (display driver) or "MachineID" (platform driver).
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