ACC-72EX User Manual
DPRAM Data Processing
58
About System and Channel Mailbox
The preferred way to address the netX operating system, rcX, is through the system mailbox. The
preferred way to address a protocol stack is through its channel mailbox. All mailboxes, however, have a
mechanism to route packets to any communication channel or the system channel. Therefore, the
destination identifier ulDest in a packet header has to be filled in according to the targeted receiver (see
the following image).
The above figure and table below illustrate the use of the destination identifier ulDest.
Value
Definition / Description
$0
Packet is passed to the netX operating system rcX
$1
Packet is passed to communication channel 0
$2
Packet is passed to communication channel 1
$3
Packet is passed to communication channel 2
$4
Packet is passed to communication channel 3
$20
Packet is passed to ‘local’ communication or system channel
Else
Reserved, Do Not Use
In regards to the channel identifier 0x00000020 (= Channel Token), the Channel Token is valid for any
mailbox. That way, the UMAC program uses the same identifier for all packets without actually knowing
which mailbox or communication channel is applied. The packet stays “local.” The system mailbox is a
little bit different because it is used to communicate to the netX operating system, rcX. The rcX has its
own range of valid command codes and differs from the communication channels.
If there is a reply packet, the netX operating system returns it to the same mailbox that the request packet
went through. Consequently, the UMAC program has to return its reply packet to the mailbox from which
the request was received.