MDDR Subsystem
Microsemi Proprietary UG0446 User Guide Revision 7.0
85
[15:13]
REG_DDRC_BURST_RDWR
0×0
001: Burst length of 4
010: Burst length of 8
100: Burst length of 16
All other values are reserved.
This controls the burst size used to access the DRAM. This
must match the BL mode register setting in the DRAM.
The DDRC and AXI controllers are optimized for a burst length
of 8.
The recommended setting is 8. A burst length of 16 is only
supported for LPDDR1. Setting to 16 when using LPDDR1 in
half/quarter bus mode may boost performance.
For systems that tend to do many single cycle random
transactions, a burst length of 4 may slightly improve system
performance.
12
Reserved
0×0
This bit must always be set to zero.
[11:5]
REG_DDRC_RDWR_IDLE_GAP
0×04 When the preferred transaction store is empty for this many
clock cycles, switch to the alternate transaction store if it is
non-empty.
The read transaction store (both high and low priority) is the
default preferred transaction store and the write transaction
store is the alternate store.
When “Prefer write over read” is set, this is reversed.
4
REG_DDRC_PAGECLOSE
0×0
1: Bank is closed and kept closed if no transactions are
available for it. This is different from auto-precharge:
(a) Explicit precharge commands are used, and not read/write
with auto-precharge and
(b) Page is not closed after a read/write if there is another
read/write pending to the same page.
0: Bank remains open until there is a need to close it (to open a
different page, or for page timeout or refresh timeout).
3
Reserved
This bit must always be set to zero.
[2:0]
REG_DDRC_LPR_NUM_ENTRIES 0×03 Number of entries in the low priority transaction store is this
value plus 1.
READ_CAM_DEPTH – (REG_DDRC_LPR_NUM_E
1) is the number of entries available for the high priority
transaction store.
READ_CAM_DEPTH = Depth of the read transaction store,
that is, 8. Setting this to maximum value allocates all entries to
low priority transaction store.
Setting this to 0 allocates 1 entry to low priority transaction
store and the rest to high priority transaction store.
Note:
In designs with ECC, number of lpr and wr
credits issued to the core is 1 less than the non-
ECC case. 1 entry each is reserved in wr and lpr
cam for storing the RMW requests arising out of
Single bit Error Correction RMW operation.
Table 65 •
DDRC_PERF_PARAM_1_CR
(continued)
Bit
Number Name
Rese
t
Valu
e
Description