PC87570 datasheet(166/168 Pages) NSC

166 / 168 page

Bootloader Description

166

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If STRPST.SHBM = 1 (read Strap Register, Shared BIOS Memory bit)

Set MCFG.SHMEM (Enable Shared BIOS Memory access)

If KBC Header Signature not valid or KBC code size equal 0

Jump to KBC_Mem_Fail (bytes 0 & 1 = signature, byte 2 = size)

If Checksum of KBC code not valid

Jump to KBC_Mem_Fail

If OEM_Detect_Crisis Address = FFFFh

Jump to KBC code entry (OEM_Detect_Crisis Address is byte 4 in KBC Header, Start of KBC code is byte

2 of KBC Header)

Else Jump to OEM_Detect_Crisis routine

OEM_Detect_Crisis routine resides in external memory and must:

1. Save RA register on entry and use its contents as a return address

2. Preserve all configuration registers xxCFG

3. Preserve Boot Program variables in RAM F000h - F0010h

4. Return with Interrupts disabled: PFAIL.EN=0, PSR.I=0

5. Return with PSR.Z = 1 if NO crisis detected

Note: It is OK for the OEM_Detect_Crisis routine to destroy stacks and interrupt dispatch table

If PSR.Z = 1 Jump to KBC code entry (Start of KBC code is byte 2 of KBC Header)

Else Jump to OEM_Mem_Fail (handle Crisis as if it were an external memory failure)

Conﬁg_Mem_Fail (come here if Configuration Block Signature is not valid)

Jump to EXT_Mem_Fail

OEM_Mem_Fail

Set OEM Failure Flag & Jump to EXT_Mem_Fail

KBC_Mem_Fail

Set KBC Failure Flag & Jump to EXT_Mem_Fail

EXT_Mem_Fail

Stacks & Dispatch table is restored (may have been modified by OEM_Detect_Crisis routine), Host Interface is turned on,

registers are initialized and program goes into a loop awaiting system input on the host interface, port 64h (port 60h is read

only because commands to the keyboard are not supported).

Commands:

90h Load RAM

Command 90h gets 4 byte of System Data: RAM address LOW, HIGH and Data array length LOW,HIGH and then

receives and loads number of bytes specified by length into the controller RAM. Ack FAh is returned to the System

if address range for Program execution was not violated. Otherwise error FFh is returned.

91h Execute

Command 91h gets 2 byte of System Data: code-label LOW, HIGH and transfer control the specified address. The

return addresses (passed in RAMAckRET and RAMErrRET variables) may be used by invoked routine to notify the

System.

92h Read Boot Status

Read Boot Status and combine it with Power Fail flag.

AAh Self Test

Since external KBC memory failure was detected, report error code FFh.

D0h, D1H Read/Write GA20

D0h - Combine actual GateA20 state with emulated 8042 output port and send data to system.

D1h - Only set/reset GateA20 line based on the system data bit 1.

PC87570 датащи(PDF) 166 Page - National Semiconductor (TI)

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