3. Data Path > Prefetching Algorithm
27
PEB383 User Manual
July 25, 2011
Integrated Device Technology, Inc.
Confidential - NDA Required
The PEB383 uses flow control buffers in the PCI Core for three categories of downstream traffic. The
amount of flow control buffer space availability is conveyed to the other end of the component using
flow control credits. The PEB383 advertises infinite credits for completions as it ensures enough buffer
space is available to store the returned completion data before initiating a read request. The PEB383
advertises initial flow control credits as follows. Each credit of data is 16 bytes.
3.5
Prefetching Algorithm
The PEB383 prefetches the data by default for the transaction that uses Memory Read Line or Memory
Read Multiple command. The PEB383 does not prefetch the data by default for the transaction that
uses the memory read command since the bridge does not know whether or not the transaction address
falls in prefetchable region.
The prefetch algorithm is configured for various commands as follows:
•
Memory read – Controlled by P_MR, MRL_66 and MRL_33 of the
.
The default value of these bits indicates that either one Dword in 32-bit bus mode or two Dwords
in 64-bit bus mode is prefetched.
•
Memory read line – Controlled by P_MRL, MRL_66 and MRL_33 of the
. The default value of these bits indicates that either 128 bytes in 32-bit bus mode or
256 bytes in 64-bit bus mode is prefetched. The PEB383 prefetches one cacheline if P_MRL is set
to 0.
•
Prefetch algorithm for memory read multiple command is controlled by P_MRM, MRM_66 and
MRM_33 of the
. The default value of these bits indicates that either
256 bytes in 32-bit bus mode or 384 bytes in 64-bit bus mode is prefetched. The PEB383
prefetches two cachelines if P_MRM is set to 0.
Table 9: Initial Credit Advertisement
Credit Type
Initial Advertisement
Posted Header (PH)
0x08
Posted Data (PD)
0x020
Non-Posted Header (NPH)
0x04
Non-Posted Data (NPD)
0x01
Completion Header (CPLH)
0x00 (Infinite)
Completion Data (CPLD)
0x000 (Infinite)