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

5 The FEEServer Control Engine
i n t hopcount ; / / E x p e c t e d v a l u e o f t h e h o p c o u n t e r f i e l d in
t h e SCSN frame a f t e r a
/ / frame has r e t u r n d from t h i s MCM t o t h e DCS
b o a r d
/ / ( d e f a u l t v a l u e : number o f MCMs in t h e
l i n k p a i r +1)
}MCMInfo ;
Listing 5.2: Structure of MCMInfo
After the data are transferred to the array the function SCSNBusBridge::calculateConfig(
void) is called. The function calculates the other values in MCMInfo.
First, SCSNBusBridge::calculateConfig(void) loops over the array mcm_info and checks
for each element if both variables line_defect and damaged are set to false. If all variables
are set to false, the linkpair has no damages. All MCMs remain unbridged and link 0 of
the linkpair is used for sending. The variables dest, hopcount and link (see listing 5.2) are
set to default values:
dest = default_slave_address,
hopcount = number_of_slaves_in_linkpair,
link = 0.
Second, it is checked if only lines in link 0 but no MCMs are broken. In this case link
1 can be used for the SCSN communication and no MCMs need to be bridged. Since
now the frames shall travel exactly the other way around compared to using link 0, dest,
hopcount and link get new values:
dest = number_of_slaves_in_linkpair−default_slave_address+1,
hopcount = default_slave_address−1,
link = 1.
If either at least one MCM in the linkpair or lines in both links are broken, the linkpair
needs to be bridged. In a first step each error is bridged seperately and the status of the
MCMs is set accordingly. Next the two outermost MCMs with status bridged are searched
and the status of all MCMs in between is set to not avaialabe. Finally the new addressing
scheme is calculated.
The procedure should be illustrated with an example. Assuming, the SCSN line in link
0 between the MCM with the slave ID 4 and 5 is broken and additionally MCM 12 is
damaged (see figure 5.6). In this case the function learnConfig(const vector
&, bool [4], int, int) has set the variable line_defect[0] for MCM 4 to true and the variable
damaged for MCM 12. In a first step calculateConfig(void) sets the status of the MCMs
4 and 5 and of the MCMs 11 and 13 to bridged. In the second step MCM 4 and MCM
13 are identified as the both outermost MCMs in bridge mode. The status of all MCMs
in between is set not avaialabe because these MCMs are not reachable any longer. In the
last step the new addressing scheme is calculated. Listing 5.3 shows the corresponding
source code for the address recalculation.
Furthermore the expected hopcounter for returning broadcasts has to be calculated.
Due to the bridging one has splitted the linkpair in two parts and therefore two values
have to be calculated, one value for each part of the linkpair (listing 5.3).
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for ( i n t s l =1; s l