The FEE Server Control Engine of the ALICE-TRD - Westfälische ...

5 The FEEServer Control Engine
The differences for SCSN_CMD_READ are small because only broadcasts require a
different handling. One would expect that sending the SCSN_CMD_READ command
to the broadcast address results in one answer frame from each MCM in the linkpair.
However, the concept of the SCSN bus hardware is one frame in – one frame out (see
section 4.3.5). Therefore the function SCSNBus::readData() which is called by execute(struct
* , unsigned, int) to handle SCSN_CMD_READ creates a separate frame with the read
command for each MCM in the linkpair. These frames are then processed as described
above.
The command SCSN_CMD_BRIDGE sets MCMs to bridge mode. It is used by SCSNBus
::learnConfig() and by the bridge test. In normal configurations this command should not
be used. Before the command is processed all remaining frames in the send buffer are sent
because a SCSN_CMD_BRIDGE always modifies the address scheme of the linkpair. The
function SCSNBus::learnConfig() creates and sends the bridge frames on its own. A bridge
request from the bridge test is processed by the function void SCSNBus::Bridging(unsigned
, unsigned, int).
The command SCSN_CMD_PAUSE has two completely different purposes, depending
on the value in the data field. The dual use of this command has historical reasons. In
both cases first the frames stored in the send buffer are sent. If the value in the data
field is bigger than 0 the program halts for the time in micro seconds given in the data
field. Such a wait command is used when the MCMs need some time to process the
previous commands. If the value in the data field is smaller than zero the status of the
state machine of the MCM named in the dest field is read. This functionality is needed
by some tests.
5.3.4 Transmission Speed
In section 4.3.5 measurements of the throughput of the SCSN bus hardware were shown.
The throughput achieved by class SCSNBus much lower because the class has to compose
the SCSN frames, send them via the SCSN bus, receive the returning frames and check
them. For a list of 5000 ping/write/read SCSN commands, it takes about 1.2 s between
the moment the class SCSNBus gets the list and the moment the class signalize that the
last frame has been received. This results in a transmission speed of 4200 frames per
second or 361.2 kBits/s. Because an SCSN frame has only 32 bit of payload (the data field
of the frame) the netto data transmission rate for the SCSN access in the control engine is
about 134.4 kBits/s.
5.4 Hardware Test Functions
The control engine of the FEEServer provides various tests to check the ROC electronics.
The tests can run only from state STDBY. The reasons for this were already discussed in
section 5.2.2. During a test is running the FSM is in the state TESTING.
All tests are mutually independent so they can be run in any order. However it is
impossible to run more then one test on a chamber concurrently. To launch a test the same
overall procedure is used as for the transition from STDBY to STDBY_CONFIGURED:
The electronics is switched on, configured and the list of SCSN commands is executed
(see section 5.2.3).
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