Receive – Interphase Tech CONDOR 4221 User Manual
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Chapter 3 - MACSI Host Interface
90
Receive
The host provides the controller with Receive commands, which specify the host resources to be used for incoming
frames. As frames come in, the controller transfers them to the specified host memory locations, updates the provided
Receive commands, and posts them back to the host.
Receive commands may be allocated to particular ports, or they may be placed in a "free pool", and the controller will
use them as needed. This is done with the ANY bit in the Command Options field. A suggested practice would be to
post a minimum number of Receive commands for each port, to prevent any port from getting starved out by activity
on other ports, and then post a pool of receives to be used by all ports.
The controller will use available internal resources to buffer incoming frames, so that the host does not have to meet
tight timing windows in order to prevent dropped packets. However, receive performance will largely be a function of
how many commands may be aggregated into a single multiple completion return, which will increase as the available
number of host-supplied commands increases.
Finally, receives posted back using the multiple completion mechanism will not be separated by port number. The host
will need to scan the list of returned frames to separate out by ports, if necessary.
Table 3-32. Receive
Receive
Offst
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0x00
Command Code
0x01
Command Options
0x02
Return Status
0x03
Normal Completion Level
Normal Completion Vector
0x04
Error Completion Level
Error Completion Vector
0x05
DMA Transfer Control Word
0x06
Buffer Address (MSW)
0x07
Buffer Address (LSW)
0x08
Reserved
0x09
Max Transfer Size / Actual Transfer Size
0x0A
Reserved
0x0B
Packet Type / Length Field
0x0C
to
0x0E
Source Address
(6 Bytes)
0x0F
Reserved
0x10
Reserved
0x11
Reserved