Toshiba TMPR7901, Руководство пользователя

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Chapter 6: SDRAM Memory Controller
TX7901 User’s Manual (Rev. 6.30T – Nov, 2001)
6-2
registers. This value must match exactly. This value effectively sets a 256 MB
region.
•
sysAddr[27:20] are compared against bits [27:20] in the LOW Decoder registers.
This value of sysAddr must be greater than or equal to the LOW decode value.
This describes the low boundary for the region.
•
sysAddr[27:20] are compared against bits [27:20] in the HIGH Decoder registers.
The value of sysAddr must be less than or equal to the HIGH decode value.
This describes the high boundary for the region.
•
If all of the above are true, then the device region is selected and the
corresponding chip select signal is activated.
Any device region can be disabled by setting the value of the “LOW” decoder to be higher
than that of the “HIGH” decoder.
The LOW and HIGH Decode Registers cannot be programmed in the region from
0x_1E00_0000 to 0x_20FF_FFFF. This is reserved for TX7901 registers and Boot Devices.
It is important to note that devices never span across region boundaries. This is detected by
reading a HIGH Register after a write. Two devices may be put in one region, but they must
not overlap.
Examples of the two-stage decoding process are shown in Figure 6-1 and Figure 6-2.
Figure 6-1 Two-stage Decoding
sysAddr[31:0]
[31:28] [27:20]
=
≥
LOW
31 28 27 20 19 0
• •
•
0 -------------------------- 0
HIGH
31 28 27 20 19 0
1 ------------------------- 1
≤
•
DIMM
Region 15
Region 1
Region 0
0xFFFF_FFFF
0x1000_0000
0x0000_0000
Can read the same value as LOW[31:28]
Physical address space
•
•
•
•
•
•
Region Boundary
Region Boundary