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Add G-REX programming documentation written by me.

    1: [[!meta title="G-REX"]]
    2: 
    3: Programming the G-REX PCI bridge
    4: version 0 - THIS IS A WORK IN PROGRESS!
    5: 
    6: # 0. Introduction
    7: 
    8: This document describes software/hardware interface of the G-REX PCI bridge for Amiga computers. What you're
    9: reading is a result of reverse engineering, which was long and difficult process. 
   10: 
   11: Next time when you're going to buy a hardware product for your Amiga, don't forget to ask the vendor to make the
   12: programming documentation publicly available! Remeber that hardware without software is just a piece of junk...
   13: and you can't write software without hardware documentation.
   14: 
   15: In case you've noticed an error in this document please let me know. 
   16: 
   17: # 1. Theory of operation
   18: 
   19: G-REX is an evolution of PCI bridge used previously on CyberVisionPPC and BlizzardVisionPPC cards. These
   20: products share a lot of similiarities.
   21: 
   22: Firmware does the dirty job of assigning PCI resources (BARs, interrupt lines, etc.) before the OS is running. 
   23: Therefore G-REX does not need any special initialization.
   24: 
   25: # 2. Memory map
   26: 
   27: G-REX is configured as multipie AutoConf boards. Confusingly, they all have the same vendor and product ID.
   28: 
   29: 0xFFFA0000 - PCI I/O register space, 64KB.
   30: 0xFFFC0000 - PCI configuration space, 128KB.
   31: 0xFFFE0000 - Bridge configuration registers, 4kB.
   32: 
   33: 0x80000000 - PCI memory space, variable size and number of boards, depending on cards installed. 
   34: 
   35: # 2a. PCI configuration space
   36: 
   37: Access to configuration space is a bit tricky. Be warned that access to addresses not used by G-REX generates bus 
   38: error (esp. to configuration locations which are unused because there is no card in the slot). Depending on how these
   39: errors are supported in your OS, it may be important to trap them and handle correctly. 
   40: 
   41: Configuration data for first slot seems to be accessible at +0x1000.
   42: 
   43: [TO BE COMPLETED]
   44: 
   45: # 2b. PCI I/O registers space
   46: 
   47: This space offers access to I/O registers of all PCI cards.
   48: 
   49: BAR addresses in this space are treated as relative to 0xFFFA0000. Card with I/O BAR set to 0x100 will actually be 
   50: available at 0xFFFA0100. 
   51: 
   52: # 2c. PCI memory space 
   53: 
   54: This space offers access to memory (and memory-mapped registers) of PCI cards. Each PCI memory BAR is assigned a 
   55: separate AutoConf board during firmware initialization. 
   56: 
   57: Addresses in this space are treated as absolute. Memory BAR register set to 0x80000000 means it is configured at this
   58: address.
   59: 
   60: # 2d. Bridge configuration registers
   61: 
   62: Offset - meaning
   63: 0x0000 - Endianness swapper mode, write 0x02 to switch bridge into big endian mode
   64: 0x0010 - Interrupt enable, write 0x01 to enable interrupts (INT2 on Amiga side)
   65: 
   66: No need to fiddle with these registers, as they've been already configured properly by the firmware.
   67: 
   68: # 3. Reconfiguring the bus.
   69: 
   70: If needed, it's possible to reconfigure bus just by writing new values into configuration space. Keep in mind that any
   71: previously initialized chips will need to be reset and initialized again (for example 3Dfx Voodoo 3, which is
   72: initialized by the firmware so it can display early startup menu). 
   73: 
   74: # 4. Interrupts
   75: 
   76: All interrupts are converted into Amiga INT2 interrupt. There's no such thing as interrupt acknowledge register.
   77: 
   78: # 5. DMA
   79: 
   80: The bridge is certainly capable of DMA, but it needs further reverse engineering.
   81: 
   82: [TO BE COMPLETED]
   83: 
   84: There were at least two different revisions of G-REX 1200. Later revision probably does support DMA in all slots.
   85: 
   86: G-REX 4000D probably has busmaster DMA capability in all slots.
   87: 
   88: # 6. Sample PCI bridge driver implementation
   89: 
   90: The NetBSD p5pb driver serves as example driver implementation. It was written using the same knowledge that went
   91: into this document.
   92: