m395t5163qz4 Samsung Semiconductor, Inc., m395t5163qz4 Datasheet - Page 13

• Manufacturer Part Number: m395t5163qz4
• Description: Ddr2 Fully Buffered Dimm
• Manufacturer: Samsung Semiconductor, Inc.

FBDIMM
DDR2 SDRAM
3.3 FBD Channel Latency
FBD channel latency is measured from the time a read request is driven on the FBD channel pins to the time when the first 16 bytes (2nd
chunk) of read completion data is sampled by the memory controller.
When not using the Variable Read Latency capability, the latency for a specific FBDIMM on an FBD channel is always equal to the latency
for any other FBDIMM on that channel. However, the latency for each FBDIMM in a specific configuration with some number of FBDIMMs
installed may not be equal to the latency for each FBDIMM in a configuration with some different number of FBDIMMs installed.
As more DIMMs are added to the FBD channel, additional latency is required to read from each DIMM on the channel. Because the FBD
channel is based on the point-to-point interconnection of buffer components between DIMMs, memory requests are required to travel
through N-1 buffers before reaching the Nth buffer. The result is that a four DIMM channel configuration will have greater idle read latency
compared to a one DIMM channel configuration.
The Variable Read Latency capability can be used to reduce latency for DIMMs closer to the host.
The idle latencies listed in this section are representative of what might be achieved in typical AMB designs. Actual implementations with
latencies less than the values listed will have higher application performance and vice versa.
3.4 Peak Theoretical Throughput
An FBD channel transfers read completion data on the FBD Northbound data connection. 144 bits of data are transferred for every FBD
Northbound data frame. This matches the 18-byte data transfer of an ECC DDR DRAM in a single DRAM command clock. A DRAM burst
of 8 from a single channel or a DRAM burst of four from two lock-stepped channels provides a total of 72 bytes of data (64 bytes plus 8
bytes ECC).
The FBD frame rate matches the DRAM command clock because of the fixed 6:1 ratio of the FBD channel clock to the DRAM command
clock. Therefore, the Northbound data connection will exhibit the same peak theoretical throughput as a single DRAM channel. For exam-
ple, when using DDR2 533 DRAMs, the peak theoretical bandwidth of the Northbound data connection is 4.267 GB/sec.
Write data is transferred on the FBD Southbound command and data connection, via Command+Wdata frames. 72 bits of data are trans-
ferred for every FBD Command+Wdata frame. Two Command+Wdata frames match the 18-byte data transfer of an ECC DDR DRAM in
a single DRAM command clock. A DRAM burst of 8 transfers from a single channel, or a burst of 4 from two lock-step channels provides
a total of 72 bytes of data (64 bytes plus 8 bytes ECC).
When the FBD frame rate matches the DRAM command clock, the Southbound command and data connection will exhibit one half the
peak theoretical throughput of a single DRAM channel. For example, when using DDR2 533 DRAMs, the peak theoretical bandwidth of
the Southbound command and data connection is 2.133 GB/sec.
The total peak theoretical throughput for a single FBD channel is defined as the sum of the peak theoretical throughput of the Northbound
data connection and the Southbound command and data connection. When the FBD frame rate matches the DRAM command clock, this
is equal to 1.5 times the peak theoretical throughput of a single DRAM channel. For example, when using DDR2 533 DRAMs, the peak
theoretical throughput of a DDR2 533 channel would be 4.267 GB/sec, while the peak theoretical throughput of an FBD-533 channel would
be 6.4 GB/sec
3.5 Hot-add
The FBDIMM channel does not provide a mechanism to automatically detect and report the addition of a new FBDIMM south of the cur-
rently active last FBDIMM. It is assumed the system will be notified through some means of the addition of one or more new FBDIMMs so
that specific commands can be sent to the host controller to initialize the newly added FBDIMM(s) and perform a hot-add reset to bring
them into the channel timing domain. It should be noted that the power to the FBDIMM socket must be removed before a hot-add FBDIMM
is inserted or removed. Applying or removing the power to a FBDIMM socket is a system platform function.
3.6 Hot remove
In order to accomplish removal of FBDIMMs, the host must perform a fast reset sequence targeted at the last FBDIMM that will be retained
on the channel. The fast reset re-establishes the appropriate last FBDIMM so that the southbound transmission outputs of the last active
FBDIMM and the southbound and northbound outputs of the FBDIMMs beyond the last active FBDIMM are disabled. Once the appropriate
outputs are disabled, the system can coordinate the procedure to remove power in preparation for physical removal of the FBDIMM if need-
ed. Note that the power to the FBDIMM socket must be removed before a hot-add FBDIMM is inserted or removed. Applying or removing
the power to a FBDIMM socket is a system platform function.
3.7 Hot replace
Hot replace of FBDIMM is accomplished through combining the hot-remove and hotadd processes
Rev. 1.3 December 2008
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