PC87570 datasheet(164/168 Pages) NSC

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Bootloader Description

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B. Bootloader Description

B.1

OVERVIEW

The bootloader program resides in the 2K on-chip ROM of

the PC87570. It provides for an orderly transfer to the BIOS

program, which resides in off-chip Flash, after power-up or

reset. The bootloader program reads the configuration and

strap pin settings after reset, and combines this information

with the BIOS configuration block settings to determine in

which mode to set the PC87570 to access the External

Memory. A number of External Memory tests (one of which

may be user-defined) are performed to verify that the BIOS

Flash is not corrupt and that control is passed to the Key-

board BIOS program. If the BIOS is corrupt, the bootloader

program accepts commands from the secondary host inter-

face (64h), which can assist the main processor in reloading

the BIOS Flash memory.

B.2

CONFIGURATION BLOCKS

The External Memory has two configuration blocks: the

System Configuration Block and the Keyboard Controller

(KBC) Header.

B.2.1

System Conﬁguration Block

The System Configuration Block is used to help set up the

PC87570 for hardware implementation (including all mem-

ory zone access times, and the size and width of the Exter-

nal Memory) and with system information (including

signature and a pointer to the KBC Header). It resides at ab-

solute address 0004h - 001Fh of the External Memory. The

System Configuration Block definitions are:

Signature byte set to E3h

Signature byte set to 8Eh

Signature byte set to 1Ch (complement of ﬁrst sig-

nature byte)

Signature byte set to 71h (complement of second

signature byte)

Length of System Conﬁguration Block set to 22 (16h)

Reserved

10 Page Register

12 Pointer to start of KBC Header (2 bytes, absolute

address)

14 Module

Conﬁguration

(MCFG),

only.

CLKOE, EXIOE & A15E bits are used. Other bits

are set by the bootloader according to the strap op-

tions (only. TEST is set directly by the strap option)

16 BIU Conﬁguration Register (BCFG)

18 IO Zone Conﬁguration Register (IOCFG)

20 Static Zone Conﬁguration Register 0 (SZCFG0),

BW set by conﬁguration pin PH.3

22 Base Memory (Boot ROM) Conﬁguration Reg 1

(SZCFG1), BW always set to 16-bit wide bus

24 PE

Pins

Alternate

Function

Enable

(PEALT)

26 - 31 Reserved

Even though some configuration registers are only a single

byte wide,16 bits have been reserved for each entry.

The bootloader does not perform a checksum of the System

Configuration Block. This means that you can change the

system configuration, by altering the configuration register

settings in the block, to serve as a debugging aid or to en-

able you to use different components (faster or slower

memory).

B.2.2

KBC Header

The KBC Header includes the following code dependent in-

formation: size, checksum and pointers to various KBC rou-

tines. Typically, it is located immediately before the KBC

BIOS, but it may exist anywhere in External Memory. The

KBC Header definitions are:

Signature byte set to 33h

Signature byte set to CCh

KBC BIOS size (not including this header)

Byte to force checksum = 0 (checksum is done on

KBC code and header, not System Conﬁguration

Block)

Pointer to user-deﬁned OEM_Detect_Crisis rou-

tine/label within BIOS code (code label, not abso-

lute address, where FFFFh signiﬁes that this

routine/label is not implemented)

Pointer to KBC BIOS entry point

A valid header has a code size that is non-zero and non-

FFh to protect against a block of zero bytes passing check-

sum. The code size has a granularity of 256 bytes allowing

a maximum size of 64K bytes (actual code size is limited to

56K bytes). Pointers to code stored in the header are code

labels generated by the compiler and assembler. To calcu-

late the actual physical address from the code label, simply

shift the code label one bit to the left to obtain the physical

address. To ensure that the checksum tests all the BIOS, be

sure that the KBC Header is at the lowest physical address

(preferably, immediately after the System Configuration

Block). The OEM_Detect_Crisis routine is intended to per-

form more extensive testing on the BIOS Flash than possi-

ble in a simple bootloader program. It can, however, be

used for other initialization and system configuration pur-

poses by strap pins.

Note:

Zero all unused memory included in the checksum

area to avoid checksum errors.

B.3

SYSTEM RESOURCES USED BY BOOTLOADER

In developing the bootloader, every effort has been made to

minimize the resources it uses and maximize the PC87570

features available to the user.

B.3.1

GPIO Pins

GPIO pins are used as an External Memory memory bus

width configuration strap and to indicate Flash memory fail-

ure. The definitions are shown in the following table.

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