LATC_XML format

Before proceeding into the details of the ConfigSystem tool, we should make some points about the LATC_XML format.

1. LATC_XML groups LATC registers by hardware component. At each level a hardware component has some registers, and controls other, lower-level, hardware components.
2. Each hardware component and each register has its own xml node.
3. For many hardware components, the LATC includes several instances of the component. In these cases LATC_XML allows us to configure a single instance by using the ``ID'' attribute of the xml node for that component. Conversely we can use ``ID='BCAST''' to configure all instances of that component.
4. Many registers can be further broken into bit-fields.
5. LATC_XML can be split into more that one file, but with several constraints. MOOT handles many of those constraints, so that they can be summarized in the next four points.
6. We must specify a broadcast value for every register which has more that one instance.
7. We must specify the value for each singleton register exactly once.
8. We may override the broadcast value for any given instance of a register exactly once.
9. We may not mix broadcast settings and specific instance settings in a single file.

The hierarchy of hardware components and hence LATC_XML nodes is shown here.

  <LATC_XML>
    <GEM>  Trigger 
      <ROI/>  ACD region of interest 
      <AOC/>  Miscellaneous trigger 
      <SCH/>  Trigger engine schedule table
      <WIN/>  Trigger window
      <TAM/>  Trigger Accept Messges, prescales, zero-suppression.
      <TIE/>  Trigger Input Enables.  
    </GEM>
    <AEM> ACD Electronics Module
      <ARC ID='[0-11] | BCAST'> ACD Readout Controller
        <AFE ID='[0-17] | BCAST'/> ACD Front-Ends
      </ARC>
    </AEM>
    <TEM ID='[0-15] | BCAST'> Tower Electronics Modules
      <TIC/>  Trigger Interface Controller
      <CCC ID='[0-3] | BCAST'> CAL Cable Controller
        <CRC ID='[0-3] | BCAST'> CAL Readout Controller
          <CFE ID='[0-11] | BCAST'/> CAL Front-Ends
        </CRC>
      </CCC>
      <TCC ID='[0-7] | BCAST'> TKR Cable Controller
        <TRC ID='[0-8] | BCAST'/> TKR Readout Controller
      </TCC>
      <SPT ID='[0-24] | BCAST'> TKR readout splits.
        <TFE ID='[0-23] | BCAST'> TKR Front-Ends.
          <TDC/> TKR Front-End DACs.
        </TFE>
      </SPT>
    </TEM>
  </LATC_XML>

The task of generating configurations is complicated by the fact that the ideal settings for many registers on a single hardware component may vary asynchronously.