Service manual

B-6 AlphaServer GS80/160/320 Service Manual
B.3.2 System Probe Commands
The second set of commands that affect cache coherency are the “system probe”
commands. These are commands that are issued from the system to the CPU
requesting data and/or Tag status updates. Probe commands are the result of a
CPU command affecting the cache of another CPU. For example, if one CPU
reads a dirty block of data that another CPU has in its cache, the system would
issue a probe command to the latter CPU, causing it to send a copy of data back
to the system and the requesting CPU.
Table B–4 lists the system probe commands that are used in the AlphaServer
GS series systems. The list is not a complete list of probe commands available
to the Alpha processor.
Table B– 4 System Probe Commands
Probe
Command
CPU Action
FRd Forwarded read command. If a processor has a dirty copy of the
requested data block in its cache, it locates the block and returns
a copy of it to the system.
FRdMod Forwarded read/modify command. If a processor has a dirty copy
of the requested data block in its cache, it locates the dirty block,
returns a copy of it to the system, and invalidates its own copy.
Inval Invalidate command. If a processor receives an invalidate
command targeting a block of data it has in its cache, it
invalidates its copy.