Embedded Solutions
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When the CRC falls on a non 32-bit boundary; the last location is padded, and the
hardware will automatically skip that location to start on the new LW boundary.
The upper and lower command words are used to provide control on a packet-by-
packet basis.
31 spare
30 Interrupt
Enable
29
Post Amble Generation
28
CRC in Hardware
27-26 spare
25-16 spare
15-10 spare
9-0
End of Packet Address
The end of packet address and the end of message address are the word addresses on
the I/O side. The address is relative to the start of each DPR section – always starts at
0x00 and ends at 0x3ff for the 1K space.
The hardware will transmit until the end of packet address is detected. The hardware
will then either stop or start a new packet based on the end of message address. The
end of message address is not checked until the end of packet, and is checked as an
absolute rather than a >= to allow roll over addressing to be used.
At the end of the packet if the Interrupt Enable bit is set an interrupt request will be
generated. Each packet can have a different setting for this bit. Once at the end of
message, interrupt on every packet, alternate packets etc.
At the end of the packet the hardware can append the post amble as defined in the
specification. If the bit is set the post amble will be added to the packet before going to
tristate, or to the idle pattern if completed, or sending the next packet if more packets
are queued. If the bit is not set the post amble is ignored and the next process started
earlier.
If the CRC in hardware bit is set then the CRC is generated by the hardware and
appended to the message. If the bit is not set then the CRC is loaded from the location
in memory immediately following the data. In either case a CRC is sent. To create a
CRC error on a given packet set the bit to “memory supplied” and provide a bogus CRC
value for the data. With the per packet control one packet can be made bad and the
rest good to test error detection and response. Due to the processing required the
Hardware option will be the “normal” option.
Due to preprocessing and hardware timing constraints the address the hardware is
working with leads the data currently being sent. The following example will help to
