INT 15 - SYSTEM - POWER-ON SELF-TEST ERROR LOG (PS50+)

	AH = 21h
	AL = subfunction
	    00h read POST log
	    01h write POST log
		BH = device ID
		BL = error code
Return: CF clear if successful
	CF set on error
	AH = status
	    00h OK
	    01h list full
	    02h unsupported subfunction
	    80h invalid command
	    86h unsupported function
	if function 00h:
	   BX = number of error codes stored
	   ES:DI -> error log
Notes:	the log is a series of words, the first byte of which identifies the
	  error code and the second the device.
	supported by AMI PCI BIOS
	IBM considers this a required BIOS function
	if the device ID is FFh, the "error code" is the actual device number
	  minus 255 (thus these devices have no specific error codes)
SeeAlso: AH=23h"SYSTEM",AH=24h"SYSTEM"