LSI Logic Confidential
SDRAM Timing
13-17
Copyright © 2001, 2002 by LSI Logic Corporation. All rights reserved.
SDRAM ATAPI/SBP DMA Throttle Register
Cbus Address: 0x30018
ATAPI/SBP Throttle Count
[11:0]
After an ATAPI request is asserted, the internal ATAPI
throttle counter is set to the host ATAPI/SBP target
throttle count. Subsequent ATAPI requests are treated as
lowest priority until the internal ATAPI throttle counter
reaches zero. After an SBP request is asserted, the
internal SBP throttle counter is set to the host ATAPI/SBP
target throttle count. Subsequent SBP requests are
treated as lowest priority until the internal SBP throttle
counter reaches zero. This allows software to spread
ATAPI and SBP DRAM loading uniformly over a field,
when the full ATAPI or SBP target bandwidth is not
needed.
13.9 SDRAM Timing
The nominal output delay of SDRAM_CLK is matched to the delays of
the other processor outputs to the SDRAMs (including SDRAM_DQ).
The actual SDRAM_CLK output delay can be adjusted in microcode to
lead the other processor outputs to the SDRAMs in increments of the
processor CLK period divided by 256. This programmable lead time
enables the SDRAM setup and hold time requirements to be met.
The tracking between SDRAM outputs and the accuracy of the lead-time
adjustment is such that for a given board layout and SDRAM
specification, a single lead-time value allows the SDRAM interface to
function over the entire range of processor process variations and
operating conditions.
Read data on SDRAM_DQ is latched internally with a read clock whose
lead time relative to the other processor outputs to the SDRAMs is
specified in microcode. The read clock tracks the other outputs
31
11
0
ATAPI/SBP Throttle Count
Содержание DMN-8600
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