
Chapter 2
AMD-761™ System Controller Programmer’s Interface
99
24081D—February 2002
AMD-761™ System Controller Software/BIOS Design Guide
Preliminary Information
Bit Definitions
DDR PDL Calibration Control (Dev0:F1:0x40)
Bit
Name
Function
31–8
Reserved
Reserved
7
SW_Recal
Software Recalibration
Software should write a 1 to this bit to cause recalibration of the PDLs. The hardware
recomputes the Cal_Delay values for all PDLs, based on the values of their SW_Cal_Dly
fields.
Status of the recalibration that was initiated by writing a 1 to this bit is also indicated in this
bit. After setting this bit, software should poll this bit until it becomes a 0 again.
0 = Calibration complete (default)
1 = Calibration not complete
If Auto_Cal_En is set, writes to this bit are ignored.
Also refer to Table 13, “PDL Calibration Modes,” on page 100.
Note:
This bit should not be set if the system clock frequency is 66 MHz.
6
Use_Act_Dly
Use Actual Delay
Software should set this bit to indicate to the hardware that it has written to the Act_Dly
fields and wants to update the PDLs (all 18) with the newly written Act_Delay values.
Software only needs to change the Act_Delay values that are not currently at their desired
values (the other Act_Dly values are simply re-applied). This method should be used only
when SW_Recal and Auto_Cal_En bits are not set.
If Auto_Cal_En is set, writes to this bit are ignored.
Also refer to Table 13, “PDL Calibration Modes,” on page 100.
This bit always returns a 0 when read.
5
Auto_Cal_En
Auto Calibration Mode
0 = Auto-calibration mode off (default)
1 = Auto-calibration mode on
When this bit is set, all of the Cal_Dly values are recomputed periodically (according to the
setting of the Auto_Cal_Period field) for all PDLs, based on the values of their SW_Cal_Dly
fields. If the Act_Dly_Inh bit is not set, the Cal_Dly values are also applied to the Act_Dly.
Also refer to Table 13, “PDL Calibration Modes,” on page 100.
Note:
Once Auto_Cal_En is set to 1, clearing it makes the bit a 0, but the Auto-Calibration
logic may perform one more update, depending on when the Auto_Cal_En bit is
cleared. Therefore, BIOS should at least wait for the amount of time specified by
the Auto_Cal_Period field after clearing the Auto_Cal_En bit before attempting to
change any of the PDL parameters.
Note:
This bit should not be set if the system clock frequency is 66 MHz.