Reference Guide

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