Intel manual Ixpbuf ixctrl Structure, Ixne IXP400 NPE Shared Structure

Intel® IXP400 Software

Buffer Management

Linux utilizes memory structures called skbuffs. The user allocates IXP_BUF and sets the data payload pointer to the skbuff payload pointer. An os_buf_ptr field inside the ixp_ctrl structure (defined below) of the IXP_BUF is used to save the actual skbuff pointer. In this manner, the OS buffers are not freed directly by the IXP400 software.

The IXP400 software IXP_BUF to skbuff mapping is a ‘zero-copy’ implementation. There is no copy/performance penalty in using Linux skbuffs. Other proprietary buffer schemes could also be implemented with the IXP400 software using the mbuf-to-skbuff implementation as an example.

ix_ctrl: Intel® IXP400 Software Internal Pool Management Fields

As shown in Figure 11, the ix_ctrl fields are set and used by the IXP_BUF pool manager provided by the OSAL component. Some of the fields can be used for specific purposes for different operating systems For example, signature verification fields is used in Linux when NDEBUG is enabled. The reserved field may be used in VxWorks to support IPv6 format.

Figure 11. IXP_BUF: ix_ctrl Structure

Reserved

Reserved

ix_signature

ix_allocated_len

ix_allocated_data

ix_pool

ix_chain

ix_osbuf_ptr

ix_ctrl: 2nd Structure of IX_BUF (Internal fields)

ix_ne: IXP400 NPE Shared Structure

As shown in Figure 12, this structure is provided by the Intel XScale core to the NPE. Depending upon the access-layer component usage, some of these fields may be visible to the user through use of macros and also may be altered by the NPE. The lower five words of this structure are defined according to the needs of NPE microcode; therefore, different NPE images may have different structure for this part. The upper three words follows the same structure across all the NPE images.

Note: Users should not make any assumptions to usage of the service-specific fields in this NPE-shared structure. The fields are for internal NPE usage only.

April 2005	IXP400 Software Version 2.0	Programmer’s Guide
42	Document Number: 252539, Revision: 007