
System Memory Controller (SMC)
MVME5100 Single Board Computer Programmer’s Reference (6806800H17B
)
226
3.2.7
Refresh/Scrub
The SMC performs refresh by doing a burst of 4 CAS-Before-RAS (CBR) refresh cycles to each
block of SDRAM once every 60 microseconds. It performs scrubs by replacing every 128th
refresh burst with a read cycle to 8 bytes in each block of SDRAM. If during the read cycle, the
SMC detects a single-bit error, it performs a write cycle back to SDRAM using corrected data
providing the SWEN control bit is set. It does not perform the write if the SWEN bit is cleared.
If the SMC detects a double-bit error, it does not perform a write.
If so enabled, single- and double-bit scrub errors are logged and the PPC60x bus master is
notified via interrupt.
3.2.8
CSR Accesses
The SMC has a set of control and status registers (CSR) that allow software to control certain
functions and to monitor some status.
3.2.9
External Register Set
The SMC has an external register chip select pin which enables it to talk to an external set of
registers. This interface is like the ROM/Flash interface but with less flexibility. It is intended for
the system designer to be able to implement general-purpose status/control signals with this
external set. Refer to
for a description of this register set.
The SMC has a mode in which two of its pins become control register outputs. When the SMC
is to operate in this mode, the External Register Set cannot be implemented. The two control
bits appear in the range where the External Register Set would have been had it been
implemented.
3.2.10 Chip Configuration
Some configuration options in the Hawk must be configured at power-up reset time before
software performs any accesses to it. The Hawk obtains this information by latching the value
on some of the upper RD signals just after the rising edge of the PURST_ signal pin. The
recommended way to control the RD signals during reset is to place pull-up or pull-down
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Страница 312: ...VMEbus Mapping Example MVME5100 Single Board Computer Programmer s Reference 6806800H17B 312...
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