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    1: [[!meta title="G-REX"]]
    2: 
    3: Programming the G-REX PCI bridge
    4: 
    5: document version 0 - THIS IS A WORK IN PROGRESS!
    6: 
    7: # 0. Introduction
    8: 
    9: This document describes software/hardware interface of the G-REX PCI bridge for Amiga computers. What you're
   10: reading is a result of reverse engineering, which was long and difficult process. 
   11: 
   12: Next time when you're going to buy a hardware product for your Amiga, don't forget to ask the vendor to make the
   13: programming documentation publicly available! Remeber that hardware without software is just a piece of junk...
   14: and you can't write software without hardware documentation.
   15: 
   16: In case you've noticed an error in this document please let me know. 
   17: 
   18: # 1. Theory of operation
   19: 
   20: G-REX is an evolution of PCI bridge used previously on CyberVisionPPC and BlizzardVisionPPC cards. These
   21: products share a lot of similiarities.
   22: 
   23: Firmware does the dirty job of assigning PCI resources (BARs, interrupt lines, etc.) before the OS is running. 
   24: Therefore G-REX does not need any special initialization.
   25: 
   26: # 2. Memory map
   27: 
   28: G-REX is configured as multipie AutoConf boards. Confusingly, they all have the same vendor and product ID.
   29: 
   30: 0xFFFA0000 - PCI I/O register space, 64KB.
   31: 
   32: 0xFFFC0000 - PCI configuration space, 128KB.
   33: 
   34: 0xFFFE0000 - Bridge configuration registers, 4kB.
   35: 
   36: 0x80000000 - PCI memory space, variable size and number of boards, depending on cards installed. 
   37: 
   38: # 2a. PCI configuration space
   39: 
   40: Access to configuration space is a bit tricky. Be warned that access to addresses not used by G-REX generates bus 
   41: error (esp. to configuration locations which are unused because there is no card in the slot). Depending on how these
   42: errors are supported in your OS, it may be important to trap them and handle correctly. 
   43: 
   44: Configuration data for first slot seems to be accessible at +0x1000.
   45: 
   46: [TO BE COMPLETED]
   47: 
   48: # 2b. PCI I/O registers space
   49: 
   50: This space offers access to I/O registers of all PCI cards.
   51: 
   52: BAR addresses in this space are treated as relative to 0xFFFA0000. Card with I/O BAR set to 0x100 will actually be 
   53: available at 0xFFFA0100. 
   54: 
   55: # 2c. PCI memory space 
   56: 
   57: This space offers access to memory (and memory-mapped registers) of PCI cards. Each PCI memory BAR is assigned a 
   58: separate AutoConf board during firmware initialization. 
   59: 
   60: Addresses in this space are treated as absolute. Memory BAR register set to 0x80000000 means it is configured at this
   61: address.
   62: 
   63: # 2d. Bridge configuration registers
   64: 
   65: Offset - meaning
   66: 0x0000 - Endianness swapper mode, write 0x02 to switch bridge into big endian mode
   67: 0x0010 - Interrupt enable, write 0x01 to enable interrupts (INT2 on Amiga side)
   68: 
   69: No need to fiddle with these registers, as they've been already configured properly by the firmware.
   70: 
   71: # 3. Reconfiguring the bus.
   72: 
   73: If needed, it's possible to reconfigure bus just by writing new values into configuration space. Keep in mind that any
   74: previously initialized chips will need to be reset and initialized again (for example 3Dfx Voodoo 3, which is
   75: initialized by the firmware so it can display early startup menu). 
   76: 
   77: # 4. Interrupts
   78: 
   79: All interrupts are converted into Amiga INT2 interrupt. There's no such thing as interrupt acknowledge register.
   80: 
   81: # 5. DMA
   82: 
   83: The bridge is certainly capable of DMA, but it needs further reverse engineering.
   84: 
   85: [TO BE COMPLETED]
   86: 
   87: There were at least two different revisions of G-REX 1200. Later revision probably does support DMA in all slots.
   88: 
   89: G-REX 4000D probably has busmaster DMA capability in all slots.
   90: 
   91: # 6. Sample PCI bridge driver implementation
   92: 
   93: The NetBSD p5pb driver serves as example driver implementation. It was written using the same knowledge that went
   94: into this document.
   95: