ACC-72EX User Manual
DPRAM Data Processing
55
DPRAM DATA PROCESSING
Since there are two processors (i.e. UMAC and netX) attempting to access data registers in Dual-Ported
Memory simultaneously, several handshaking modes can be used to guarantee data consistency. Each
sub-block defines the type of handshaking, if any, it requires. The ACC-72EX Setup Assistant software
output file lists the type of handshaking required for each of the sub-blocks available on the COMX
module.
Should handshaking not be used, collision circuitry on the gateway will, in the very least, guarantee
consistency within single byte boundaries.
Non-Cyclic Data Exchange
The mailbox of a communication channel or system channel has two areas that are used for non-cyclic
message transfer to and from the netX.
Send Mailbox (System / Communication Channel)
Packet transfer from UMAC to netX firmware
Receive Mailbox (System / Communication Channel)
Packet transfer from netX firmware to UMAC
For a communication channel, send and receive mailbox areas are used by fieldbus protocols, providing a
non-cyclic data exchange mechanism. Another use of the mailbox system is to allow access to the
firmware running on the netX chip for diagnostic and identification purposes. The
send mailbox
is used
to transfer cyclic data
to
the network or
to
the netX. The
receive mailbox
is used to transfer cyclic data
from
the network or
from
the netX. Modbus Plus or Ethernet TCP/IP is an example of a fieldbus
protocol which utilizes a non-cyclic data exchange.
Whether or not a mailbox is used depends on the function of the firmware.
Note
Each mailbox can hold one packet at a time. netX stores packets in an
internal packet queue; these packets are not retrieved by UMAC. This
queue has limited space and may fill up, so new packets may be lost.
To avoid these deadlock situations, it is strongly recommended to
empty the mailbox frequently, even if packets are not expected by the
UMAC program. Unexpected command packets should be returned to
the sender with an Unknown Command in the status field; unexpected
reply messages can be discarded.
Message or Packets
The non-cyclic packets obtained through the netX mailbox have the following structure:
Hilscher Documentation
ACC-72EX Setup Assistant
Sy
st
em
B
lo
ck
Se
nd
M
ai
lbo
x
usPackagesAccepted
SSMB_usPackagesAccepted
ulDest
SSMB_ulDest
ulSrc
SSMB_ulSrc
ulDestId
SSMB_ulDestId
ulSrcId
SSMB_ulSrcId
ulLen
SSMB_ulLen
ulId
SSMB_ulId
ulState
SSMB_ulState
ulCmd
SSMB_ulCmd
ulExt
SSMB_ulExt
ulRout
SSMB_ulRout
…
SSMB_ultData0 .. SSMB_ultData20
