ADSP-BF535 Blackfin Processor Hardware Reference
18-41
External Bus Interface Unit
The user must ensure that
tRAS + tRP >= max(tRC,tRFC,tXSR)
.
Note that these timing parameters should not be changed while the
SDC is active. Therefore, since the SDC is enabled by default upon
reset, the SDC must be disabled after reset to allow for modifica-
tions to the default
EBIU_SDGCTL
bit values.
The
PFE
bit is used to enable or disable the SDC read buffer. When
PFE = 1
, the SDC speculatively prefetches (reads) a subsequent cache line
in order to improve performance on cache misses. Clearing the
PFE
bit
causes any data in the read buffer to be invalidated and disables
prefetching.
When the read buffer is enabled (
PFE = 1
), SDC prefetching can poten-
tially take bus bandwidth away from the Asynchronous Memory
Controller (AMC), because the external bus is shared between the SDC
and the AMC. By clearing the
PFP
bit, the amount of bandwidth taken
from the AMC is limited; when an AMC access needs the external bus,
prefetching halts, and the AMC can use the pins immediately after the
completion of prefetch reads that were already in progress. It should be
noted that although clearing
PFP
limits the bandwidth taken from the
AMC, it does not restore the AMC bandwidth to what it is when prefetch-
ing is disabled (
PFE = 0
). When
PFP
is set to 1, prefetching takes priority
over AMC accesses. This means that the read buffer prefetches an entire
cache line before releasing the external bus to the AMC for a pending
AMC access.
Refer to
“Read Buffer (Prefetch) Operation” on page 18-72
for more
information.
The
PSM
and
PSSE
bits work together to specify and trigger an SDRAM
power-up (initialization) sequence. If the
PSM
bit is set to 1, the SDC does
a Precharge All command, followed by a Load Mode Register command,
and then does eight Auto-Refresh cycles. If the
PSM
bit is cleared, the SDC
Содержание ADSP-BF535 Blackfin
Страница 80: ...Development Tools 1 26 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 312: ...Working With Memory 6 86 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 332: ...System Interfaces 7 20 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 360: ...Dynamic Power Management Controller 8 28 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 446: ...Beginning and Ending an SPI Transfer 10 40 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 522: ...Timing Examples 11 76 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 562: ...IrDA Support 12 40 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 608: ...PCI I O Issues 13 46 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 672: ...References 14 64 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 810: ...SDRAM Controller SDC 18 86 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 811: ...ADSP BF535 Blackfin Processor Hardware Reference 18 87 External Bus Interface Unit...
Страница 812: ...SDRAM Controller SDC 18 88 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 860: ...DMA Bus Debug Registers 20 30 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 908: ...SDRAM Controller External Bus Interface Unit B 36 ADSP BF535 Blackfin Processor Hardware Reference...