2-8
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Raven PCI Host Bridge & Multi-Processor Interrupt Controller
2
The PPC bus transfer types generated by the PPC master depend on the
PCI command code and the INV/GBL bits in the PCISATTx registers. The
GBL bit determines whether or not the GBL* signal is asserted for all
portions of a transaction and is fully independent of the PCI command
code and INV bit. The following table shows the relationship between PCI
command codes and the INV bit.
The PPC master incorporates an optional operating mode called Bus Hog.
When Bus Hog is enabled, the PPC master will continually request the
PPC bus for the entire duration of each PCI transfer. When Bus Hog is not
enabled, the PPC master will structure its bus request actions around its
desire to perform couplets. This means the bus request will be deasserted
between couplets. Caution should be exercised when using this mode since
the over-generosity of bus ownership to the PPC master can be detrimental
to the host CPU’s performance. The Bus Hog mode can be controlled by
the BHOG bit within the GCSR. The default state for BHOG is disabled.
Table 2-2. PPC Transfer Types
PCI Command Code
INV
PPC Transfer Type
PPC Transfer Size
TT0-TT4
Memory Read,
Memory Read
Multiple,
Memory Read Line
0
Read
Burst/Single Beat
01010
Memory Read,
Memory Read
Multiple,
Memory Read Line
1
Read With Intent to
Modify
Burst/Single Beat
01110
Memory Write,
Memory Write and
Invalidate
x
Write with Kill
Burst
00110
Memory Write,
Memory Write and
Invalidate
x
Write with Flush
Single Beat
00010