ibm3206k0424 ETC-unknow, ibm3206k0424 Datasheet - Page 248

• Manufacturer Part Number: ibm3206k0424
• Description: Ibm Processor For Network Resources
• Manufacturer: ETC-unknow

IBM3206K0424
IBM Processor for Network Resources
Preliminary
Virtual Memory Overview
Each virtual buffer consists of a number of real buffers. For each virtual buffer there is a buffer map that
defines the size and number of real buffers that may be allocated to the virtual buffer. Each map is built from
a common template (the VIMEM Virtual Buffer Segment Size Register) that associates 1 to n buffer indexes
in the map to a real buffer in one of the four real buffer regions defined in VIMEM. In VIMEM, the Buffer Map
Base Address Register defines the size of the map and therefore also the number of buffer indexes in the vir-
tual buffer map. Each eight-byte entry of the map contains the pool ID of the pool to which the buffer is allo-
cated plus space for three real buffer segment indexes. This implies the smallest map yields a virtual buffer of
one to four real buffer segments (three real buffer segments plus the implicit real buffer that all virtual buffers
are allocated). The biggest map defines a virtual buffer of 1-16 real buffer segments (15 plus the implicit one).
The intention of this structure is to allow the user to customize the value in the Virtual Buffer Segment Size
Register to utilize memory in an efficient manner relative to network data traffic. For example, if network traffic
contained 50% packets of < 512 bytes, 35% packets of < 1K bytes, and the rest was < 5K bytes, the user
could set up Virtual Memory to use three real segments of 512 bytes, 512 bytes, and 4K bytes respectively.
The incoming data would neatly fit into the segments and minimize wasted memory.
POOLS and VIMEM maintain the maps for the virtual buffers. On a write that crosses a real buffer boundary
into an as yet an unresolved region of a virtual buffer, a page fault occurs. When a page fault occurs, POOLS
determines whether or not a real buffer can be assigned. If it can be assigned, the index of the real buffer rel-
ative to the base address of the particular buffer size is placed by VIMEM into the buffer map. The first buffer
is implicitly associated with the Virtual Memory address for a particular virtual buffer and enough real memory
must be available to support the first real buffer of each virtual buffer at initialization time. There is not neces-
sarily enough real storage for all the possible real buffers associated with a virtual buffer.
Buffer Pool Management (POOLS)
pnr25.chapt04.01
Page 248 of 676
August 14, 2000