3. Processor Bus Interface
88
PowerSpan II User Manual
80A1010_MA001_09
Integrated Device Technology
www.idt.com
Because PowerSpan II does not have a cache, all read and write transfer types are treated the same. For
example, a Read with Intent to Modify command (PB_TT= 01110) is handled the same way as a Read
Atomic command (PB_TT= 11010).
PowerSpan II performs PCI read prefetches and stores read data in an internal buffer when the Prefetch
Keep (PRKEEP) bit is set to 1. The purpose of a prefetch read is to fetch read information before the
master requests the information. If the master then requests the information the target can respond
immediately with the prefetched information. This ability protects the master from slow access times
for information it requires. However, when a write is performed to a prefetched address, a subsequent
read could yield stale data. In order to guarantee there is no stale data, set the PRKEEP bit to 0. This
function disables the internal buffer to ensure there is no stale data. By setting this PRKEEP bit to 0
PowerSpan II is unable to perform PCI read prefetches and read performance may be decreased in the
system.
10000
eieio
11000
tlb invalidate
00001
lwarx
01001
tlb sync
01101
icbi
Reads
01010
Read
01110
Read with intent to modify
11010
Read Atomic
11110
Read with intent to modify atomic
01011
Read with no intent to cache
Writes
00010
Write with flush
00110
Write with kill
10010
Write with flush atomic
Prefetching attributes for each image map must meet the system’s cache coherency
requirements
Table 13: PowerSpan II PB Slave Transfer Types
TT[0:4]
Name