AMD Geode LX CS5536 Handmatig - Pagina 5
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46959A - March 2009
cally supportable. As an example, consider the follow-
ing DIMM characteristics:
CAS#
Min Cycle
Latency
Time (ns)
CL=5
CL=4
CL=3
This is has a fundamental access time of 15ns, and
therefore at CL=2, the minimum cycle time should be
7.5ns. This DIMM should be function normally at
133MHz, with a CL setting of 2.
6)
Program the CAS_LAT field of the MC_CF8F_DATA
register with the CAS# Latency value (i.e., 2). Addi-
tional settings are programmed in the same register:
THZ_DLY: This adds 1 clock to the Read-Write turn-
around time
TRUNC_DIS: This forces bursts of 4, preventing bursts
of 2 (unsupported in DDR2)
7)
Program the memory controller with the appropriate
latencies for the memory. For DDR2, this step is nearly
identical to DDR technology. As a result, this docu-
ment will not go into many details. The memory con-
troller
settings
affected
MC_CF8F_DATA register, and are determined by SPD
data:
Field
Parameter
ACT2PRE
PRE2ACT
ACT2CMD
ACT2ACT
ACT2ACTREF
REF2ACT*
* REF2ACT is in the MC_CF1017_DATA register.
**Contains an extension value, new for DDR2.
8)
Program other timing control parameters. In the
MC_CF1017_DATA register:
WR_TO_RD (tWTR) should be set for 2 clocks.
RD_TMG_CTL should be set for 4 half-GLIU clocks
9)
Set
the
drive
strength
MC_CF07_DATA) to Reduced if the DIMM(s) support
it. This feature is indicated in SPD[22], bit 0.
The memory controller is now set up correctly, and is pre-
pared for turning on the memory. Now follow the DDR2
memory initialization steps (as outlined Table 2-1 on page
1).
AMD Geode™ LX Processor DDR2 BIOS Porting Guide
Max Cycle
Time (ns)
3.0
8.0
3.75
8.0
5.0
8.0
are
fields
in
Timing
SPD Byte
tRAS
30
tRP
27
tRCD
29
tRRD
28
tRC
41/40**
tRFC
42/40**
control
(EMR_DRV
3.3.2
SDRAM Initialization
1)
CKE may have already been asserted, due to the
requirement of the On-DIMM CPLD. If not, assert CKE
by
clearing
MC_CFCLK_DBUG register. CKE needs to be
asserted for at least 400ns before executing step 2.
Also, set REF_STAG in MC_CF07_DATA to 4 clocks.
2)
Issue a PRECHARGE ALL command. The memory
controller does not allow software to issue a single
PRECHARGE ALL command. Instead, the command
is inserted before a REFRESH or a LOAD MODE
command.
Set
MC_CFCLK_DBUG register to insert the PRE-
CHARGE ALL.
Additionally,
requires that A[10] be set high. This presents a minor
architectural problem. The BIOS will not have the
opportunity to modify A[10] between the PRE-
CHARGE ALL command and the subsequent LOAD
MODE command. So the CPLD must be prepared for
the LOAD MODE command to EMR(2) (i.e., the A[n]
and BA[n] bits set in its registers) and A[10] also set to
high.
3)
Issue a LOAD MODE command to EMR(2). First set
the
the CPLD's registers. Typical settings are REG_A=00h
and
REG_B=C4h.
SW_EN#=1, BA[1:0]=10b, and A[10]=1. Next, in
MC_CF07_DATA register, set MSR_BA to 10b and
PROG_DRAM to 1. Then clear PROG_DRAM and
FORCE_PRE.
Note that DDR2 defines A[10] of EMR(2) should be
programmed to 0. Setting A[10]=1 for the PRE-
CHARGE ALL step causes a violation of the spec dur-
ing the LOAD MODE command. However, AMD has
not observed any side effects of programming EMR(2)
with A[10]=1.
4)
Issue a LOAD MODE command to EMR(3). Similar to
the previous step, set the CPLD's registers. Typical
settings are REG_A=00h and REG_B=E0h. The set-
ting in REG_B is SW_EN#=1, BA[1:0]=11b. Next, in
MC_CF07_DATA register, set MSR_BA=11b and
PROG_DRAM=1. Then clear PROG_DRAM.
5)
Issue a LOAD MODE command to EMR(1) to enable
the DLL. Program the CPLD with the appropriate infor-
mation for the EMR(1) definition. Note that in certain
cases, it might be appropriate to leave the DLL dis-
abled to allow the DRAM to run at lower frequencies.
in
AMD does not recommend omitting this step, however.
DLL Enable is defined in b[0] of the EMR(1) register.
The desired setting goes into REG_A[0]. Also, the set-
ting for the drive strength control goes into REG_A[1].
If previously set up, these two bits may be retrieved
from the MC_CF07_DATA register. All other A[n] bits in
the
MASK_CKEn
bit(s)
the
FORCE_PRE
the
PRECHARGE
ALL
The
setting
in
in
the
bit
in
the
command
REG_B
is
5