5-180
Bus Interface
AMD-K5 Processor Technical Reference Manual
18524C/0—Nov1996
5.4.6
Special Bus Cycles
The processor drives D/C = 0, M/IO = 0, and W/R = 1 to define a
special bus cycle. The values of these cycle-definition signals
are the same for all special cycles. Only BE7–BE0 and A31–A3
differentiate among the special cycles, as shown in Table 5-23.
This function of BE7–BE0 bears no relationship to the D63–D0
data bus. It is particularly apparent in the case of the branch-
trace message special bus cycle, during which the value of
BE7–BE0 is DFh (1101_1111b) but, in contradiction to the byte-
enable bits, the four bytes on D31–D0 carry valid data during
both cycles of the operation. During the first cycle, D31–D0
carries the EIP value of the source (branch) instruction. Dur-
ing the second cycle, D31–D0 carries the EIP value of the
branch-target instruction.
Table 5-23. Encodings For Special Bus Cycles
BE7–B0
A31–A3
Special Bus Cycle
1
Cause
FEh
...00h
Shutdown
Triple fault
FDh
...00h
Cache Invalidation
INVD instruction
FBh
...10h
Stop Grant
STPCLK
FBh
...00h
Halt
HLT instruction
F7h
...00h
Cache Writeback and Invalidation
WBINVD instruction
EFh
...00h
FLUSH Acknowledge
FLUSH
DFh
...00h
Branch-Trace Message
2
Bit 5 = 1 and bits 3–1 = 001 in the hardware
configuration register (HWCR). See Section
7.1 on page 7-3 for details.
Notes:
1. For all special bus cycles, D/C = 0, M/IO = 0 and W/R = 1. System logic must return BRDY in response to this cycle.
2. The message in a branch-trace message special bus cycle is different in the AMD-K5 and Pentium processors.
Summary of Contents for AMD-K5
Page 1: ...AMD K5 Processor Technical Reference Manual TM...
Page 10: ...x AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 24: ...1 4 Overview AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 54: ...2 30 Internal Architecture AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 116: ...4 26 Performance AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 356: ...6 44 System Design AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 380: ...7 24 Test and Debug AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 396: ...A 16 AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 406: ...I 10 Index AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...