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    1: [[!meta title="G-REX"]]
    2: 
    3: Programming the G-REX PCI bridge
    4: 
    5: document version 0.1 - 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 
   21: BlizzardVisionPPC cards. These products share a lot of similiarities (at 
   22: least when it comes to PCI interface). 
   23: 
   24: Firmware does the dirty job of assigning PCI resources (BARs, interrupt lines, 
   25: etc.) before the OS is running. Therefore G-REX does not need any special 
   26: initialization.
   27: 
   28: # 2. Memory map
   29: 
   30: G-REX is configured as multipie AutoConf boards. Confusingly, they all have the same vendor (8512) and product (101).
   31: 
   32: 0xFFFA0000 - PCI I/O register space, 64KB.
   33: 
   34: 0xFFFC0000 - PCI configuration space, 128KB.
   35: 
   36: 0xFFFE0000 - Bridge configuration registers, 4kB.
   37: 
   38: 0x80000000 - PCI memory space, variable size and number of boards, depending on cards installed. 
   39: 
   40: # 2a. PCI configuration space
   41: 
   42: Access to configuration space is a bit tricky. Be warned that access to 
   43: addresses not used by G-REX generates bus error (esp. to configuration 
   44: locations which are unused because there is no card in the slot). Depending on 
   45: how these errors are supported in your OS, it may be important to trap them and
   46: handle correctly. 
   47: 
   48: Configuration data for first slot seems to be accessible at +0x1000.
   49: 
   50: [TO BE COMPLETED]
   51: 
   52: # 2b. PCI I/O registers space
   53: 
   54: This space offers access to I/O registers of all PCI cards.
   55: 
   56: BAR addresses in this space are treated as relative to 0xFFFA0000. Card with 
   57: I/O BAR set to 0x100 will actually be available at 0xFFFA0100. 
   58: 
   59: # 2c. PCI memory space 
   60: 
   61: This space offers access to memory (and memory-mapped registers) of PCI cards. 
   62: Each PCI memory BAR is assigned a separate AutoConf board during firmware 
   63: initialization. 
   64: 
   65: Addresses in this space are treated as absolute. Memory BAR register set to 
   66: 0x80000000 means it is configured at this address.  
   67: 
   68: # 2d. Bridge configuration registers
   69: 
   70: Offset - meaning
   71: 
   72: 0x0000 - Endianness swapper mode, write 0x02 to switch bridge into big endian mode
   73: 
   74: 0x0010 - Interrupt enable, write 0x01 to enable interrupts (INT2 on Amiga side)
   75: 
   76: No need to fiddle with these registers, as they've been already configured properly by the firmware.
   77: 
   78: # 3. Reconfiguring the bus.
   79: 
   80: If needed, it's possible to reconfigure bus just by writing new values into 
   81: configuration space. Keep in mind that any previously initialized chips will 
   82: need to be reset and initialized again (for example 3Dfx Voodoo 3, which is
   83: initialized by the firmware so it can display early startup menu). 
   84: 
   85: # 4. Interrupts
   86: 
   87: All interrupts are converted into Amiga INT2 interrupt. There's no such thing 
   88: as interrupt acknowledge register.
   89: 
   90: # 5. DMA
   91: 
   92: The bridge is certainly capable of DMA, but it needs further reverse 
   93: engineering.
   94: 
   95: [TO BE COMPLETED]
   96: 
   97: There were at least two different revisions of G-REX 1200. Later revision 
   98: probably does support DMA in two slots.
   99: 
  100: G-REX 4000D probably has busmaster DMA capability in all slots.
  101: 
  102: # 6. Sample PCI bridge driver implementation
  103: 
  104: The NetBSD [[p5pb|http://netbsd.gw.com/cgi-bin/man-cgi?p5pb+4.amiga+NetBSD-current]] 
  105: driver serves as an example driver implementation. It was written using the 
  106: same knowledge that went into this document.
  107: 
  108: The driver consists of several files in [[src/sys/arch/amiga/pci|http://nxr.netbsd.org/xref/src/sys/arch/amiga/pci/]] directory.
  109: 
  110: p5membar.c - Dummy driver handling AutoConf resources.
  111: p5membarvar.h - Structures used by the p5membar.
  112: p5pb.c - Main driver code.
  113: p5pbreg.h - Inlcude file containing register locations.
  114: p5pbvar.h - Structures used by the p5pb.
  115: 
  116: The p5pb does attach on top of p5bus, however p5membar drivers attach on top of zbus (since 8512/101 entries are seen as Zorro boards).
  117: