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Chapter 4 47

POST Check Points

When POST executes a task, it uses a series of preset numbers called check point to be latched at port 80h,

indicating the stages it is currently running. This latch can be read and shown on a debug board.

The following table describes the Acer common tasks carried out by POST. A unique check point number

represents each task.

Checkpoint Description

CFh Test CMOS R/W functionality

C0h Early chipset initialization:

• Disable shadow RAM

• Disable L2 Cache (socket 7 or below)

• Program basic chipset registers

C1h Detect memory

• Auto-detection of DRAM size, type and ECC.

• Auto-detection of L2 cache (socket 7 or below)

C3h Expand compressed BIOS code to DRAM

C5h Call chipset hook to copy BIOS back to E000 & F000 shadow

RAM

0h1 Expand the Xgroup codes locating in physical address 1000:0

02h Reserved

03h Initial Superio_Early_Init switch

04h Reserved

05h

1. Blank out screen

2. Clear CMOS error flag

06h Reserved

07h

1. Clear 8042 interface

2. Initialize 8042 self-test

08h

1. Test special keyboard controller for Winbond 977

series Super I/O chips

2. Enable keyboard interface

09h Reserved

0Ah

1. Disable PS/2 mouse interface (optional)

2. Auto detect ports for keyboard & mouse followed by a

port & interface swap (optional)

3. Reset keyboard for Winbond 977 series Super I/O

chips

0Bh Reserved

0Ch Reserved

0Dh Reserved

0Eh Test F000h segment shadow to see whether it is R/W-able or not.

If test fails. keep beeping the speaker.

0Fh Reserved

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