Problem with AMD HDT setup for Tyan S2885 - LinuxBIOS debugging

[Ken Fuchs]

Purpose:

    To use AMD's HDT hardware/software to debug LinuxBIOS on various
    mainboards and chipsets.

    Two HDT headers were added to a commercial Tyan S2885 board.

Here's my hardware setup:

    S2885 with HDT CPU0 header <-> HDT ribbon cable
           and HDT CPU1 header <-> HDT ribbon cable

    HDT ribbon cable <-> HDT Multiprocessor Adapter
    HDT ribbon cable <-> |

    HDT Multiprocessor Adapter <-> Macraigor Systems' OCDemon (Raven)

    OCDemon (Raven) <-> parallel cable <-> host EPP mode port

Power up sequence:

    1) Host
    2) Target
    3) OCDemon (Raven)
    4) HDT MP Adapter

Symptoms of the problem:

    1) OCDemon host and target lights never go on.

    2) When using the host HDT software to open a new workspace, only 1
       processor is shown as available.

    3) While completing the opening of this single processor workspace, a
       warning window with the text below pops open:

       +--------------------------------------------+
       |Communication between HDT and               |
       |Processor No. 0 has problem!                |
       |                                            |
       |Please check your HDT host                  |
       |and target TAP connections.                 |
       |                                            |
       |Do you want to continue with incorrect info?|
       +--------------------------------------------+
    
Possible clue to the solution:

    Missing TDI/TDO jumpers or jumper headers?  There is a 2x3 header
    pad (no header) directly between the P1 socket and the P0 DIMM
    sockets that could be the correct place for these jumper headers.
    Maybe all I need to do is add a 2x3 header there and trace the
    routes of the six pins, hopefully back to the P0's HDT connector?
    (I don't have access to the S2885's schematics.)

    It seems that MP HDT must be enabled in this way.  I know that
    reference boards have toggle switches for this purpose.

Please respond with your suggestions.

Thank you very much!

Sincerely,

Ken Fuchs <kfuchs at winternet.com>