User’s Manual
APPENDIX D: AMIBIOS POST Check Point List
AMIBIOS provides all IBM standard Power On Self Test (POST) routines as well as enhanced AMIBIOS POST routines. The POST routines support CPU internal diagnostics. The POST checkpoint codes are accessible via the Manufacturing Test Port (I/O port 80h).
Whenever a recoverable error occurs during the POST, the system BIOS will display an error message describing the message and explaining the problem in detail so that the problem can be corrected.
During the POST, the BIOS signals a checkpoint by issuing one code to I/O address 80H. This code can be used to establish how far the BIOS has executed through the
If the BIOS detects a terminal error condition, it will halt the POST process and attempt to display the checkpoint code written to port 80H. If the system hangs before the BIOS detects the terminal error, the value at port 80H will be the last test performed. In this case, the terminal error cannot be displayed on the screen. The following POST checkpoint codes are valid for all AMIBIOS products with a core BIOS date of 07/15/95 version 6.27 (Enhanced).
Uncompressed Initialization Codes — The uncompressed initialization checkpoint hex codes are listed in order of execution:
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| Code | Description |
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| D0 | NMI is disabled. CPU ID saved. INIT code checksum verification will |
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| be started. |
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| D1 | Initializing the DMA controller, performing the keyboard controller BAT |
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| test, starting memory refresh, and going to 4GB flat mode. |
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| D3 | To start memory sizing. |
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| D4 | Returning to real mode. Executing any OEM patches and setting the |
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| stack next. |
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| D5 | Passing control to the uncompressed code in shadow RAM at |
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| E000:0000h. The INIT code is copied to segment 0 and control will be |
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| transferred to segment 0. |
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| D6 | Control is in segment 0. Next, checking if <Ctrl><Home> was pressed |
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| and verifying the system BIOS checksum. If either <Ctrl><Home> was |
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| pressed or the system BIOS checksum is bad, next will go to |
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| checkpoint code E0h. Otherwise, going to checkpoint code D7h. |
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| D7 | To pass control to interface module. |
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| D8 | Main BIOS runtime code is to be decompressed. |
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| D9 | Passing control to the main system BIOS in shadow RAM next. |
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