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32 lines
2.0 KiB
Markdown
32 lines
2.0 KiB
Markdown
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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 original SWIM chip supported Group Coded Recording (GCR)-formatted floppy disks in 400 kb and 800 kb formats, while the newer SWIM2 and SWIM3 chips include support for 1.44 MB floppies in MFM format.
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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 predecessors, it allowed some DMA capability to transfer read or write data.
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The floppy drives themselves were provided by Sony.
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Some New World Macs such as Rev. A iMac G3s do have a SWIM 3 driver present, but this normally goes unused due to no floppy drive being connected.
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# Registers
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| Offset | Functionality |
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|:------:|:-------------------------------:|
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| 0x0 | Data |
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| 0x1 | Timer |
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| 0x2 | Error |
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| 0x3 | Parameter Data |
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| 0x4 | Phase |
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| 0x5 | Setup |
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| 0x6 | Read Mode (Read), Mode (Write) |
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| 0x7 | Handshake (Read), Mode (Write) |
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| 0x8 | Interrupt |
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| 0x9 | Step |
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| 0xA | Current Track |
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| 0xB | Current Sector |
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| 0xC | Gap/Format |
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| 0xD | First Sector |
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| 0xE | Sectors to Transfer |
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| 0xF | Interrupt Mask |
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