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ZCOM Tables and Data Structures

Message Header

Chapter 3112

Message Header

In the buffer header (i.e., BFDATA pointer), there is a message header

that describes the message type, the source and destination addresses,

and the type of response expected from the message. The message header

is the first 30 bytes of the buffer data area. When the data buffer is

allocated, the initial data offset is chosen so that the message data starts

on a specific boundary depending on its purpose (e.g. for a inbound DMA

buffer, the data area must be on a 64-byte boundary). For inbound DMA

buffer, enough space is left at the end of the buffer so that the final

64-byte boundary is within the buffer area but beyond the end of the

data area. These boundary limits ensure that the DMA reads and writes

will not cause side effects by corrupting other buffers. Besides, the size of

the buffer is rounded up to a multiple of 8-bytes, to satisfy the 64-bit

alignment which is needed for the 64-bit kernel.

Message Header (zmhd_type)

Table 3-33 shows the information in the message header (zmhd_type).

Table 3-33 Message Header (zmhd_type)

Field Name Field Description Field Type

Size

(Bytes)

MID Message ID header struct 24

MRQ Message request block struct 6

1 2 ... 107 108 109 110 111 112 113 114 115 116 117 ... 327 328

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