AMD Geode LX 800@0.9W - Manual (Page 512)

512 AMD Geode™ LX Processors Data Book
Security Block 33234H
6.11.2.1 EEPROM ID Interface
The EEPROM ID interface provides an interface to an
EEPROM non-volatile memory available for storing ID
numbers, keys, or other security related information. The
EEPROM ID interface consists of a 2K (256-byte) array
with 2 bytes reserved for EEPROM control state, 238 bytes
are available as general purpose non-volatile storage, and
16 bytes reserved for use as a hidden key for the AES
engine. (Note that locations 18-33 are reserved for a
Unique ID, but can be used for general purpose storage.)
After reset, the EEPROM ID interface state machine reads
the two access control bytes from the EEPROM. These
define the access policies for the EEPROM. It also auto-
matically copies the 128-bit hidden key from the array to
the AES engine’s hidden key register. When an
AMD Geode LX processor device is initially manufactured,
the EEPROM is programmed to all ones and the control
bytes are set to the unlocked state allowing writing of the
entire EEPROM array and reading of all location except the
hidden key. Information can be stored in the EEPROM and
then optionally the EEPROM can be locked to prevent fur-
ther writes and/or disable certain debug features of the
AMD Geode LX processor.
The EEPROM controller defaults to the unlocked state if it
cannot access an EEPROM after reset. This allows parts
built without EEPROMs to have functional debug inter-
faces.
The EEPROM ID interface works on a byte-wide basis. The
EEPROM Address register (SB Memory Offset 804h) is
first programmed by software, and then the EEPROM
Command register (SB Memory Offset 804h) is written to
initiate a write from the EEPROM Data register (SB Mem-
ory Offset 808h) to the array or a read from the array to the
Data register. The START bit in the Command register (SB
Memory Offset 800h) resets automatically once the
EEPROM access has completed. The user may also
enable an interrupt to be generated when the access has
completed. Since the EEPROM access is slow, this simple
command interface allows the processor to continue with
other tasks while waiting for the access to complete. Table
6-77 shows common usage of the EEPROM.
Note: The EEPROM interface is designed to work with a
GLIU frequency up to 400 MHz. For operation
above 400 MHz, several internal design parame-
ters must be changed.
6.11.2.2 Security Block Interrupts
The Security Block has three possible sources for an inter-
rupt: completion of an AES task on context A, completion
of an AES task on context B, and completion of an
EEPROM read or write operation. The interrupt event and
interrupt mask registers are memory mapped. These three
sources can also generate an SMI. The SMI event and SMI
mask registers are accessible via MSRs. Any one of these
events will simultaneously set the SMI and interrupt event
bits. The mask bits may be used to enable either an inter-
rupt or an SMI if desired.
6.11.2.3 GLIU Interface
The GLIU provides a standard interface to the AMD Geode
LX processor. The Security Block is both a master and a
slave on this bus.
Table 6-77. EEPROM Address Map
Byte Address Range Description
0 Lower Access control byte 0 (WPU and WPL)
1 Access control byte 1 (WPE and DBL)
2-17 Hidden key storage (128 bits)
18-33 Unique ID (128 bits)
34-127 User data
128-255 Upper User data