INT 15h, 21h (33)          Read or Write POST Error Log           PS/2

        Used internally by BIOS in Power-On Self Test (POST).

   AL = 00 Read POST Error Log

             On entry:          AH     21h

                                AL      00 . Read POST Error Log

             Returns:           ES:DI   Address of POST Error Log
                                BX      Number of POST error codes stored
                                CF      0
                                AH      00h

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   AL = 01h Write Error to POST Log

             On entry:          AH     21h

                                AL      01 . Write to POST Error Log

                                BX      POST 16-bit error code
                                        BH = device code
                                        BL = device error

         Returns:               CF      = 0 . success
                                        = 1 . log is full

                                AH      = 0 . success, error stored
                                        = 1 . log is full, error not stored

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     This service is used by BIOS during the Power-On Self Test (POST). If
     errors occur, they are recorded in the POST log. The Power-On Self Test
     is concerned with hardware; there is little of value to the applications
     programmer in this service.

     If you want to read the POST log, use Subservice 00h. On return,
     ES:DI will point to the error log, which contains two-byte POST error
     codes.

     To place error codes in the POST log (only BIOS should do this), use
     Subservice 01h. Place the 16-bit error in BX (BH = device code, BL
     = device error). If the carry flag is not set on return, the error has
     been stored in the log.