Intel PXA255 - Manual (Page 261)

Intel® PXA255 Processor Developer’s Manual 6-79
Memory Controller
11. Optionally, in systems that contain SDRAM or Synchronous Static memory, enable auto-
power-down by setting MDREFR[APD].
6.12 GPIO Reset Procedure
On a GPIO Reset, the Memory Controller registers keep the values they had before the reset. No
new configuration programming is required. However, SDRAM refreshes do not occur during the
reset time. After nRESET_OUT is deasserted, the memory controller will continue refreshing. By
ensuring a refresh time for SDRAM that is smaller than the default, it is possible to preserve the
SDRAM contents. To do this, follow this procedure:
The SDRAM refresh time is chosen by taking the specified refresh time, typically 64 ms, and
subtracting the GPIO Reset time (found in the Intel® PXA255 Applications Processors Electrical,
Mechanical, and Thermal Specification). For example, the GPIO Reset time is ~360 microseconds,
leaving an SDRAM refresh time of (64 ms - .360 ms) = 63.64 ms. Use this time to program the
MDREFR[DRI].
In the boot code, determine the type of reset. If the reset was a GPIO reset, then refresh all the
SDRAM rows. Refreshing all the SDRAM rows preserves their value in case GPIO reset occurs
again.
After all the SDRAM rows have been refreshed, enable GPIO reset
6.13 Memory Controller Register Summary
Table 6-40 shows the registers associated with the memory interface and the physical addresses
used to access them. These registers must be mapped as non-cacheable and non-bufferable and can
only be a single word access. They are grouped together in one page and all have the same memory
protections.
Table 6-40. Memory Controller Register Summary (Sheet 1 of 2)
Physical Address Symbol Register Name
0x4800_0000 MDCNFG SDRAM Configuration Register
0x4800_0004 MDREFR SDRAM Refresh Control Register
0x4800_0008 MSC0 Static Memory Control Register 0
0x4800_000C MSC1 Static Memory Control Register 1
0x4800_0010 MSC2 Static Memory Control Register 2
0x4800_0014 MECR
Expansion Memory (16-bit PC Card / Compact Flash) Bus
Configuration register
0x4800_001C SXCNFG Synchronous Static Memory Control Register
0x4800_0024 SXMRS MRS value to be written to SMROM
0x4800_0028 MCMEM0
Card interface Common Memory Space Socket 0 Timing
Configuration
0x4800_002C MCMEM1
Card interface Common Memory Space Socket 1 Timing
Configuration
0x4800_0030 MCATT0 Card interface Attribute Space Socket 0 Timing Configuration
0x4800_0034 MCATT1 Card interface Attribute Space Socket 1 Timing Configuration
0x4800_0038 MCIO0 Card interface I/O Space Socket 0 Timing Configuration