PRELIMINARY SPECIFICATION
13-1
System Boot
Chapter 13
by Gert Slavenburg, Bob Bradfield, and Hani Salloum
13.1
BOOT SEQUENCE OVERVIEW
In this document, the generic PNX1300 name refers
to the PNX1300 Series, or the PNX1300/01/02/11
products.
Before a PNX1300 system can begin operating, the
main-memory interface (MMI) registers and on-chip
clock ratio register must be configured. Since the
DSPCPU cannot begin operating until after these regis-
ters and circuits are initialized, the DSPCPU cannot be
relied on to initialize these resources. Consequently,
PNX1300 needs an independent bootstrap facility for
low-level initialization.
PNX1300 implements low-level system initialization by
combining a small block of on-chip system boot logic with
a single external serial boot EEPROM connected to the
I
2
C interface. See
Figure 13-1
. Serial EEPROMs with an
I
2
C interface are slow but have the advantages of being
space-efficient and inexpensive. The amount of informa-
tion needed for initial system boot is small, so speed is
not a concern.
The PNX1300 system boot block performs differently for
each of two major types of PNX1300 system, distin-
guished by host-assisted and autonomous bootstrap-
ping. The most significant bit of the tenth byte in the ex-
ternal EEPROM determines the system boot procedure
and must match the system configuration.
In host-assisted bootstrapping, a PNX1300 device is in-
tegrated into a system where some other processor
serves as the host. For example, a PNX1300 chip might
be part of a PCI card in a standard personal computer
(PC). In this case, the PNX1300 system boot only needs
to load enough information from the serial EEPROM to
configure the on-chip timing circuits and MMI; the host
processor can perform all other PNX1300 setup chores.
In the second type of system, autonomous bootstrapping
takes place. In this configuration, a PNX1300 device
serves as the host (main) processor; consequently, the
PNX1300 system boot must perform more work. In addi-
tion to configuring on-chip timing and the MMI, the sys-
tem boot must set the base addresses of the main mem-
ory and MMIO address apertures and load into main
memory a level 1 bootstrap program for the DSPCPU.
Only the first 10 bytes of the serial EEPROM are needed
when PNX1300 is not the host PCI processor; thus, such
systems can use a very low-cost 128-byte EEPROM de-
vice. When PNX1300 serves as the system
’
s host pro-
cessor, the boot logic permits almost 2 KB of storage for
the level 1 bootstrap DSPCPU program in a single eight-
pin EEPROM device.
Figure 13-1. The system boot logic uses the I2C in-
terface to access a serial EEPROM that contains
main-memory and system timing information.
4
PNX1300
System Boot
Block
I
2
C Interface
Serial
EEPROM
SCL
SDA
4
V
dd
Table 13-1. System Boot Features
Characteristic
Comments
Boot Configurations
Supported
Host assisted, e.g., PNX1300 is a
PCI slave in a standard PC.
Autonomous, e.g., PNX1300 is the
host PCI processor.
Single standard I
2
C serial
EEPROMs from 128 bytes to 2KB in
size.
EEPROMs connect via the
PNX1300 built-in 2-wire I
2
C inter-
face.
The use of EEPROMs with hard-
ware Write Protect (WP) is recom-
mended. A jumper on WP allows
user control over in-system repro-
gramming using the I
2
C interface.
The EEPROM must respond to I
2
C
device address 1010.
Atmel 24C01A (128 bytes, WP)
Atmel 24C08 (1KB, WP)
Atmel 24C16 (2KB, WP).
From 128 bytes to 2 KB (one
device) for initial program load.
ROM Device Types
Supported
ROM device
examples
ROM size