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38 lines
1.7 KiB
Markdown
38 lines
1.7 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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# BMac
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The BMac is an ethernet controller.
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The max frame size is 0x5EE bytes.
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It resides on 0xF3011000, with Writing DMA on 0xF3008200 and Reading DMA on 0xF3008300.
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Swim3 is located at 0xF3015000.
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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 0xF3013000 for the printer, and the other at 0xF3013020 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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# 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. 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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The floppy drives themselves were provided by Sony.
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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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# 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 OpenFirmware), the ""systemReg" (display driver) or "MachineID" (platform driver).
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