Acer Aspire ZS600, Service Manual

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4-6 Troubleshooting
Checkpoints
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A checkpoint is either a byte or word value output to I/O port 80h. The BIOS outputs
checkpoints throughout bootblock and Power-On Self Test (POST) to indicate the task the
system is currently executing. Checkpoint sare very useful in aiding software developers or
technicians in debugging problems that occur during the pre- boot process.
Viewing BIOS checkpoints
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Viewing all checkpoints generated by the BIOS requires acheckpoint card, also referred to
as a POST card or POST diagnostic card. These are ISA or PCI add-in cards that show the
value of I/O port 80h on a LED display. Checkpoints may appear on the bottom right corner of
the screen during POST. This display method islimited, since it only displays checkpoints that
occur after the video card has been activated.
Bootblock Initialization Code Checkpoints
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The Bootblock initialization code sets up the chipset, memory, and other components before
system memory is available. The following table describes the type of checkpoints that may
occur during the bootblock initialization portion of the BIOS.
NOTE: NOTE :
Please note that checkpoints may differ between different platforms based on system
configuration. Checkpoints may change due to vendor requirements, system chipset or
option ROMs from add-in PCI devices.
Table 4-2.
Checkpoint Description
Before D0 If boot block debugger is enabled, CPU cache-as-RAM functionality is
enabled at this point. Stack will be enabled from this point.
D0 Early Boot Strap Processor (BSP) initialization like microcode update,
frequency and other CPU critical initialization. Early chipset initialization
is done.
D1 Early super I/O initialization is done including RTC and keyboard
controller. Serial port is
enabled at this point if needed for debugging. NMI is disabled. Perform
keyboard controller BAT test. Save power-on CPUID value in scratch
CMOS. Go to flat mode with 4GB limit and GA20 enabled.
D2 Verify the boot block checksum. System will hang here if checksum is
bad.
D3 Disable CACHE before memory detection. Execute full memory sizing
module. If memory sizing module not executed, start memory refresh and
do memory sizing in Boot block code. Do additional chipset initialization.
Re-enable CACHE. Verify that flat mode is enabled.
D4 Test base 512KB memory. Adjust policies and cache first 8MB. Set
stack.