Scope, Description, Initialization Steps

AMD Geode™ LX Processor DDR2 BIOS Porting Guide

1.0Scope

The AMD Geode™ LX processor has an integrated DDR memory controller. Due to the concerns over the availability and increasing cost of DDR, AMD has developed a method for operating DDR2 memory with the processor’s memory controller. This application note details the software changes necessary to enable this technology.

Note: The solution described in this document does not conform to the JEDEC DDR2 Specification. This solution may not work with all DDR2 memory.

Note: This is revision B of this document. The change from revision A (also dated March 2009) is “AMD Confidential” was removed.

2.0Description

Initializing DDR2 SDRAM requires writing to additional mode registers. In addition to the Mode Register (MR) and Extended Mode Register (EMR), DDR2 defines two new Extended Mode Registers, EMR(2) and EMR(3). The EMR is renamed as EMR(1). Furthermore, the MR and EMR definitions are not an exact match between DDR and DDR2. Table 2-1shows a comparison of the typical initial- ization steps for DDR vs. DDR2.

Addressing MR vs. EMR(1), EMR(2) or EMR(3) is deter- mined by the states of BA[2:0] while the LOAD MODE com- mand is presented on the control signals. The data written to the registers is the pattern presented on A[15:0] when the command is initiated. (Note, however, that A[15:13]=0, and BA[2]=0 in all cases.)

Software on the LX processor issues LOAD MODE com- mands by writing the MC_CF07_DATA register. During the operation, the memory controller (MC) uses various bits and fields in the MC_CF07_DATA and MC_CF8F_DATA registers. With the available settings, the LX processor is not capable of generating the necessary signal patterns for all the required LOAD MODE commands.

Table 2-1. Initialization Steps

DDR	DDR2

Wait a minimum of 200µs	Wait a minimum of 200µs
after clocks and power are	after clocks and power are
stable, then assert CKE.	stable, then assert CKE.

Wait a minimum of 400ns,	Wait a minimum of 400ns,
then issue a PRE-	then issue a PRE-
CHARGE ALL command.	CHARGE ALL command.

	Issue a LOAD MODE
	command to EMR(2)

	Issue a LOAD MODE
	command to EMR(3).

Issue a LOAD MODE	Issue a LOAD MODE
command to EMR to	command to EMR(1) to
enable the DLL.	enable the DLL.

Issue LOAD MODE com-	Issue LOAD MODE com-
mand to MR with DLL	mand to MR with DLL
reset.	reset.

Wait at least 200 clock	Wait at least 200 clock
cycles. Issue a PRE-	cycles. Issue a PRE-
CHARGE ALL command.	CHARGE ALL command.

Issue two REFRESH	Issue two REFRESH
commands.	commands.

Issue LOAD MODE to MR	Issue LOAD MODE to MR
without DLL reset.	without DLL reset.

	Issue LOAD MODE to
	EMR(1) with OCD default.

	Issue LOAD MODE to
	EMR(1) with OCD exit.

SDRAM initialization is	SDRAM initialization is
complete.	complete.

46959A - March 2009