
SDRAM Controller
8-5
GMS30C7201 Data Sheet
8.4
SDRAM Control Registers
The SDRAM controller has three registers: the configuration, refresh timer and the
Write Buffer Flush timer. The configuration register
’
s main function is to specify the
number of SDRAMs connected, and whether they are 2- or 4-bank devices. The refresh
timer gives the number of
BCLK
ticks that need to be counted in-between each refresh
period. The Write Buffer Flush timer is used to set the number of
BCLK
ticks since the
last write operation, before the write buffer
’
s contents are transferred to SDRAM.
In addition to the SDRAM control registers, the ARM may access the SDRAM mode
registers by writing to a 64MByte address space referenced from the SDRAM mode
register base address. Writing to the SDRAM mode registers is discussed further in
8.5
Power-up Initialization of the SDRAMs
on page 8-10.
8.4.1 Configuration Register
Address:
SDRAM register base address
The SDRAM controller configuration register is a 32-bit wide split read/write register,
such that bits [23:0] should be configured by the ARM, and bits [31:24] provide status
information that are read-only.
All locations containing
“
-
”
are for future expansion, and should always be programmed
with the binary value 0. Writes to bits [31:24] are always ignored.
E
[3:0]
Device Enable - indicates that there is a physical SDRAM present in
each of the four slots in the address map. This bit is used to determine
whether an auto-refresh command should be issued to a particular
memory device.
slot 0 - address range 0
–
16Mbyte
slot 1 - address range 16
–
32MByte
slot 2 - address range 32
–
48MByte
slot 3 - address range 48
–
64MByte
Value = 1 if a device is present
Value = 0 if a device is not present
B
[3:0]
Indicates whether the SDRAM in the slot is a 2- or 4-bank device
Address
Name
Description
SDRAMCBase + 0x00
ConfigReg
#32-bit R/W
SDRAMCBase + 0x04
RefreshTmr
#16-bit R/W
SDRAMCBase + 0x08
Write buffer flush
timer
#3-bit R/W
Table 8-4: SDRAM controller registers
31
23
15
7
0
S
1
S
0
-
-
-
-
-
R
A
C
1
C
0
D
C
W
P
E
3
B
3
-
-
E
2
B
2
-
-
E
1
B
1
-
-
E
0
B
0
-
-