4.6 KiB
ROM
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.
New World ROMs are 1 MB stubs containing OpenFirmware and some basic drivers, but has an additional ROM stored on the Mac's hard disk to provide Toolbox functionality. The ROMs stored on the Mac's hard disk also had updates distributed.
Within Apple, the project to overhaul Mac OS ROM code from separate portable, low-end, and high-end branches into a single codebase was called SuperMario.
Serial
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.
DBDMA
The Description-Based Direct Memory Access relies on memory-based descriptions, minimizing CPU interrupts.
| Channel | Number |
|---|---|
| SCSI0 | 0x0 |
| FLOPPY | 0x1 |
| ETHERNET TRANSMIT | 0x2 |
| ETHERNET RECIEVE | 0x3 |
| SCC TRANSMIT A | 0x4 |
| SCC RECIEVE A | 0x5 |
| SCC TRANSMIT B | 0x6 |
| SCC RECIEVE B | 0x7 |
| AUDIO OUT | 0x8 |
| AUDIO IN | 0x9 |
| SCSI1 | 0xA |
NCR 53C94
The NCR 53C94 is the SCSI controller.
Register Map
| Offset | Read functionality | Write functionality |
|---|---|---|
| 0x0 | Transfer counter LSB | Transfer counter LSB |
| 0x1 | Transfer counter MSB | Transfer counter MSB |
| 0x2 | FIFO | FIFO |
| 0x3 | Command | Command |
| 0x4 | Status | Destination Bus ID |
| 0x5 | Interrupt | Select/reselect timeout |
| 0x6 | Sequence step | Synch period |
| 0x7 | FIFO flags/sequence step | Synch offset |
| 0x8 | Configuration 1 | Configuration 1 |
| 0x9 | Clock conversion factor | |
| 0xA | Test mode | |
| 0xB | Configuration 2 | Configuration 2 |
| 0xC | Configuration 3 | Configuration 3 |
| 0xF | Reserve FIFO Byte (Cfg 2) |
SWIM 3
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).
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.
Unlike its predecessor, it allowed some DMA capability.
The floppy drives themselves were provided by Sony.
Some New World Macs do have a SWIM 3 driver present, but this normally goes unused due to no floppy drive being connected.
NVRAM
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.
On a physical machine, one has to hold the Command/Apple, Option, P and R keys together. However, using DingusPPC, one can simply delete the nvram.bin file instead.
PMU
| Command Name | Number | Functionality |
|---|---|---|
| PMUpMgrADB | 0x20 | Send ADB command |
| PMUpMgrADBoff | 0x21 | |
| PMUxPramWrite | 0x32 | |
| PMUtimeRead | 0x38 | |
| PMUxPramRead | 0x3A | |
| PMUmaskInts | 0x70 | |
| PMUreadINT | 0x78 | |
| PMUPmgrPWRoff | 0x7E | |
| PMUResetCPU | 0xD0 |
USB
FireWire
Present in several New World Macs is a FireWire controller. Mac OS Classic normally only supports FireWire 400.
Miscellaneous
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In order for the mouse to move, it generally needs to use the Vertical Blanking Interrupt (VBL) present on the video controller. However, the Pippin instead uses a virtual timer task to accomplish, as there is a bug that prevents the VBL from working in the Taos graphics controller.
-
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).