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AMD-761™ System Controller Programmer’s Interface
Chapter 2
AMD-761™ System Controller Software/BIOS Design Guide
24081D—February 2002
Preliminary Information
Bit Definitions
BIU0 Status/Control (Dev0:F0:0x60)
Bit
Name
Function
31
Prb_En
Probe Enable
0 = Probes are not sent to this processor.
1 = Probes are sent to this processor.
30
Reserved
This bit must be programmed to zero for normal operation.
29
Reserved
This bit must be programmed to zero for normal operation.
28
Reserved
This bit must be programmed to zero for normal operation.
27–25
Xca_Prb_Cnt
Xca Probe Count
This bit field represents the maximum number of consecutive AMD Athlon™ processor
system bus grants for probe data movement types that are allowed before letting another
type have the bus.BIOS must program this field to a non-zero value for proper operation.
The recommended value to be loaded in this field by BIOS software is 0x2.
24–22
Xca_RD_Cnt
Xca Read Count
This bit field represents the maximum number of consecutive AMD Athlon processor
system bus grants for read data movement types that are allowed before letting another
type have the bus.BIOS must program this field to a non-zero value for proper operation.
The recommended value to be loaded in this field by BIOS software is 0x6.
21–19
Xca_WR_Cnt
Xca Write Count
This bit field represents the maximum number of consecutive AMD Athlon processor
system bus grants for write data movement types that are allowed before letting another
type have the bus.BIOS must program this field to a non-zero value for proper operation.
The recommended value to be loaded in this field by BIOS software is 0x6.
18
Halt_Discon_En
Halt Disconnect Enable
0 = No AMD Athlon system bus disconnect is performed following HALT.
1 = AMD Athlon system bus disconnects after receiving a HALT special cycle.
17
Stp_Grant_
Discon_En
Stop Grant Disconnect Enable
0 = No AMD Athlon processor system bus disconnect is performed following STOP/GRANT.
1 = AMD Athlon processor system bus disconnects after receiving a STOP/GRANT special cycle.
16–14
Prb_Limit
Probe Limit
BIOS software initializes this field with the maximum number of outstanding probes that
the given CPU can handle. The default is a single probe. Encoding is as follows:
0b000 = 1 probe
0b001 = 2 probes
................................
0b111 = 8 probes
13–10
Ack_Limit
Ack Limit
BIOS software reads this field to determine how many outstanding unacknowledged
AMD Athlon processor system bus commands can be sent to the AMD-761™ system
controller. The AMD-761 system controller allows a maximum of four unacknowledged
commands. Encoding is as follows:
0b0000 = 1 unacknowledged command
0b0001 = 2 unacknowledged commands
..........................................................
0b1111 = 16 unacknowledged commands