128 MBytes
64 MBytes
32 MBytes
16 MBytes
Base address
Mask field
CS size
Mask field
(16-MBytes minimum granularity)
(Chip-select decoding allowing
maximum CS size = 256 MBytes)
A26
A29
A25
A28
A24
A27
A23
A0
... ...
0
0
0
1
0
0
1
1
0
1
1
1
1
1
1
1
A26
A29
A25
A28
A24
A27
A26 A25 A24
128 MBytes
1 GBytes
64 MBytes
512 MBytes
32 MBytes
256 MBytes
16 MBytes
A27
256 MBytes
0
0
0
0
GPMC
7.1.3.3.8.1 Chip-Select Base Address and Region Size
Any external memory or ASIC device attached to the GPMC external interface can be accessed by any
device system host within the GPMC 512-Mbyte contiguous address space. For details, see
The GPMC 512 Mbyte address space can be divided into a maximum of seven chip-select regions with
programmable base address and programmable CS size. The CS size is programmable from 16 Mbytes
to 256 Mbytes (must be a power-of-2) and is defined by the mask field. Attached memory smaller than the
programmed CS region size is accessed through the entire CS region (aliasing).
Each chip-select has a 6-bit base address encoding and a 4-bit decoding mask, which must be
programmed according to the following rules:
•
The programmed chip-select region base address must be aligned on the chip-select region size
address boundary and is limited to a power-of-2 address value. During access decoding, the register
base address value is used for address comparison with the address-bit line mapping as described in
(with A0 as the device system byte-address line). Base address is programmed through the
GPMC_CONFIG7_i[5-0] BASEADDRESS bit field.
•
The register mask is used to exclude some address lines from the decoding. A register mask bit field
cleared to 0 suppresses the associated address line from the address comparison (incoming address
bit line is don't care). The register mask value must be limited to the subsequent value, based on the
desired chip-select region size. Any other value has an undefined result. When multiple chip-select
regions with overlapping addresses are enabled concurrently, access to these chip-select regions is
cancelled and a GPMC access error is posted. The mask field is programmed through the
GPMC_CONFIG7_i[11-8] MASKADDRESS bit field.
Figure 7-6. Chip-Select Address Mapping and Decoding Mask
A mask value of 0010 or 1001 must be avoided because it will create holes in the chip-select address space.
Chip-select configuration (base and mask address or any protocol and timing settings) must be performed
while the associated chip-select is disabled through the GPMC_CONFIG7_i[6] CSVALID bit. In addition, a
chip-select configuration can only be disabled if there is no ongoing access to that chip-select. This
requires activity monitoring of the prefetch or write-posting engine if the engine is active on the chip-select.
Also, the write buffer state must be monitored to wait for any posted write completion to the chip-select.
264
Memory Subsystem
SPRUH73H – October 2011 – Revised April 2013
Copyright © 2011–2013, Texas Instruments Incorporated