Freescale Semiconductor MPC8260 - Manual (Page 449)

Memory Controller
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
Freescale Semiconductor 11-31
11.3.10 60x Bus-Assigned SDRAM Refresh Timer (PSRT)
The 60x bus assigned SDRAM refresh timer register (PSRT) is shown in Figure 11-16 .
Table 11-15 describes PSRT fields.
11.3.11 Local Bus-Assigned SDRAM Refresh Timer (LSRT)
The local bus-assigned SDRAM refresh timer register (LSRT) is shown in Figure 11-17 .
Table 11-14. Local Bus-Assigned UPM Refresh Timer (LURT)
Bits Name Description
0–7 LURT Refresh timer period. Determines the timer period according to the following equation:
This timer generates a refresh request for all valid banks that selected a UPM machine assigned to
the local bus (M
x MR[BSEL] =1) and is refresh-enabled (M x MR[RFEN] =1). Each time the timer
expires, a qualified bank generates a refresh request using the selected UPM. The qualified banks
are rotating their requests.
Example: For a 25-MHz system clock and a required service rate of 15.6 µs, given
MPTPR[PTP] = 31, the LURT value should be 11 decimal. (12*32)/25 MHz = 15.36 µs, which is less
than the required service period of 15.6 µs.
0 7
Field PSRT
Reset 0000_0000
R/W R/W
Addr 0x0x1019C
Figure 11-16. 60x Bus-Assigned SDRAM Refresh Timer (PSRT)
Table 11-15. 60x Bus-Assigned SDRAM Refresh Timer (PSRT)
Bits Name Description
0–7 PSRT Refresh timer period. Determines the timer period according to the following equation:
This timer generates refresh requests for all valid banks that selected a SDRAM machine assigned
to the 60x bus and is refresh-enabled (PSDMR[RFEN] = 1). Each time the timer expires, all banks
that qualify generate a bank staggering auto refresh request using the SDRAM machine. See
Section 11.4.10, “SDRAM Refresh .”
Example: For a 25-MHz system clock and a required service rate of 15.6 µs, given
MPTPR[PTP] = 31, the PSRT value should be 11decimal. (12*32)/25 MHz = 15.36 µs, which is less
than the required service period of 15.6 µs.
TimerP eriod
LURT 1 + ( ) MPTPR PTP [ ] 1 + ( ) ×
Bus Frequency
----------------------------------------------------------------------------------------
⎝ ⎠
⎛ ⎞
=
TimerPeriod
PSRT 1 +
( )
MPTPR PT P
[ ] 1
+
( ) ×
Bus Frequency
---------------------------------------------------------------------------------------
⎝ ⎠
⎛ ⎞
=