
Sun Microelectronics
118
UltraSPARC User’s Manual
Figure 7-22
P_REPLY Packet Format (Cycle 2 not present in all P_REPLYs)
P_REPLYs take either one or two interconnect clock cycles. The first cycle con-
tains the P_REPLY type, and the Class bit. The second cycle, if present, contains
the Master ID (MID) of the UltraSPARC that generated the original request.
Table 7-17 shows the P_REPLY encodings and the number of cycles in each pack-
et.
The Class values are indicated as follows:
•
0=hardwired to 0
•
X=don't care
•
C=Copied from the P_REQ packet
With the exception of P_FERR, UltraSPARC generates all P_REPLYs as an ac-
knowledgment to a previous SC request. UltraSPARC can assert P_FERR at any
time to indicate a fatal error requiring system reset. upon seeing P_FERR from
any UltraSPARC, SC should assert RESET_L to all interconnect ports.
Table 7-17
P_REPLY Encoding
Type
Cycles
Name
Reply to Transaction
Class
Type
P_IDLE
1
Idle
Default State
0
0000
P_FERR
1
Fatal Error
All transactions, any time
X
0100
P_RERR
2
Read Data Error
P_NCBRD_REQ
C
0101
P_SNACK
2
Coherent S_REQ Non Existent ACK
S_REQ
C
0111
P_RAS
2
Read ACK Single
P_NCRD_REQ
C
1000
P_SACK
2
Coherent S_REQ ACK
S_REQ
C
1010
P_IAK
2
Interrupt Acknowledge
P_INT_REQ
C
1100
P_SACKD
2
Coherent S_REQ Dirty Victim ACK
S_REQ
C
1101
Class
Type
Master ID (MID)
Cycle 2
Cycle 1
4
3
0
4
0
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