<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html> <head> <title></title> <link rel="stylesheet" media="screen" type="text/css" href="./style.css" /> <link rel="stylesheet" media="screen" type="text/css" href="./design.css" /> <link rel="stylesheet" media="print" type="text/css" href="./print.css" /> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> </head> <body> <h1 class="sectionedit1947"><a name="data_structure_design_discussion" id="data_structure_design_discussion">Data structure design discussion</a></h1> <div class="level1"> </div> <!-- EDIT1947 SECTION "Data structure design discussion" [1-48] --> <h1 class="sectionedit1948"><a name="concept_diagram" id="concept_diagram">Concept diagram</a></h1> <div class="level1"> <p> (Inspired by gnetman, by Bill Cox) </p> <p> <a href="/./lib/exe/fetch.php?hash=d4505f&media=http%3A%2F%2Fwww2.eng.cam.ac.uk%2F~pcjc2%2Fgeda%2Fdatastructures.png" class="media" title="http://www2.eng.cam.ac.uk/~pcjc2/geda/datastructures.png"><img src="media/http///www2.eng.cam.ac.uk/~pcjc2/geda/datastructures.png" class="media" alt="" /></a> </p> </div> <!-- EDIT1948 SECTION "Concept diagram" [49-178] --> <h2 class="sectionedit1949"><a name="concepts_behind_the_structures" id="concepts_behind_the_structures">Concepts behind the structures</a></h2> <div class="level2"> </div> <!-- EDIT1949 SECTION "Concepts behind the structures" [179-222] --> <h3 class="sectionedit1950"><a name="design" id="design">Design</a></h3> <div class="level3"> <p> This is might not exist as a “file”, as such, but exists as a data structure entity to be the owner of the circuits required in a particular design. The “root circuit” is the uppermost level of hierarchy. </p> </div> <!-- EDIT1950 SECTION "Design" [223-446] --> <h3 class="sectionedit1951"><a name="circuit" id="circuit">Circuit</a></h3> <div class="level3"> <p> A <strong>circuit</strong> entity is the key concept in this model. It defines an electrical block by a its external connections (<strong>MPort</strong>s). A schematic is one way of representing a circuit, hence a circuit object may own or more <strong>page</strong> of schematics. </p> <p> We may also define a <strong>symbolic</strong> (graphic) representation of a circuit - this is like a schematic <strong>page</strong>, however its representation should fit within a single sheet. The minimum a symbolic representation must contain is the <strong>pins</strong> which connect it to higher levels of circuit hierarchy. </p> </div> <!-- EDIT1951 SECTION "Circuit" [447-1004] --> <h3 class="sectionedit1952"><a name="mport" id="mport">MPort</a></h3> <div class="level3"> <p> If it is to be useful as a re-usable block, a sub-<strong>circuit</strong> must expose electrical connectivity for a parent <strong>circuit</strong> to connect with. Each such connection is represented by an <strong>Mport</strong> (Master port). This term (re-used from gnetman) represents the fact that once a circuit is instantiated, we need to differentiate between the connections of each specific instance. This is done with instance specific <strong>Port</strong> structures. The <strong>port</strong>s point back at the <strong>Mport</strong>s (master ports) of the circuit representation. </p> </div> <!-- EDIT1952 SECTION "MPort" [1005-1541] --> <h3 class="sectionedit1953"><a name="instance" id="instance">Instance</a></h3> <div class="level3"> <p> A <strong>circuit</strong> represents a re-usable electrical entity which we may replicate at various points in our design hierarchy. This is done by instantiating the sub-<strong>circuit </strong> in a higher level of hierarchy. Each instance is associated with an <strong>Instance</strong> structure, which is a placeholder for instance specific attributes such as the sub-circuit's hierarchical refdes. </p> </div> <!-- EDIT1953 SECTION "Instance" [1542-1929] --> <h3 class="sectionedit1954"><a name="attrib" id="attrib">Attrib</a></h3> <div class="level3"> <p> An <strong>Attrib</strong> defines meta-data attached which might be attached to a <strong>circuit</strong>, a <strong>circuit</strong>'s <strong>Mport</strong>, a specific <strong>circuit</strong> <strong>instance</strong>, or a <strong>Net</strong>. </p> <p> In a break from gEDA's current <strong>attrib</strong> model, it makes sense to associate the meta-data directly with the particular entity it pertains to, rather than the graphic representation. This is because some forms of sub-<strong>circuit</strong> entity may be defined without a schematic, and could still require this meta-data. It will be possible to reference any <strong>attrib</strong> within the realm of a <strong>circuit</strong> for display on its schematic <strong>page</strong>(s) where that is desired. </p> </div> <!-- EDIT1954 SECTION "Attrib" [1930-2569] --> <h3 class="sectionedit1955"><a name="netlist" id="netlist">Netlist</a></h3> <div class="level3"> <p> A <strong>Netlist</strong> defines the electrical connectivity of a <strong>circuit</strong>. It owns a number of <strong>Net</strong>s, which individually represent a single connection between <strong>Mport</strong>s belonging to this <strong>circuit</strong>, and <strong>ports</strong> of instantiated sub-<strong>circuits</strong>. </p> <p> Initially, it is likely there will only be one netlist for a <strong>circuit</strong> - the one constructed from processing the electrically relevant objects on <strong>page</strong>(s) of the <strong>circuit</strong>'s schematic. </p> <p> Future developments may see multiple netlists for a circuit, possibly some generated / written in an HDL language, and critically, re-exported from a layout package (e.g. PCB). It will be possible to identify and flag up differences in connectivity throughout a design flow, be that from HDL to schematic, or schematic to layout. </p> <p> This has real applications in back-annotation and in design verification. </p> </div> <!-- EDIT1955 SECTION "Netlist" [2570-3435] --> <h3 class="sectionedit1956"><a name="net" id="net">Net</a></h3> <div class="level3"> <p> A <strong>net</strong> associates with structures forming a given electrical connection within this <strong>circuit</strong>. </p> <p> As we also have a graphical representation of the wires (<strong>ConnSegment</strong>s) which make up this connection, each <strong>Net</strong> can be associated with multiple <strong>ConnSegment</strong>s. The association to <strong>Pins</strong> representing <strong>Mport</strong>s of this <strong>circuit</strong> and to the <strong>Pins</strong> of any instantiated sub-<strong>circuits</strong> is made via a <strong>net</strong>'s association to the appropriate <strong>Mport</strong> and <strong>port</strong> structures. </p> </div> <!-- EDIT1956 SECTION "Net" [3436-3940] --> <h3 class="sectionedit1957"><a name="page" id="page">Page</a></h3> <div class="level3"> <p> A <strong>page</strong> is a canvas for placing graphical objects representing a circuit. A <strong>page</strong> can be used to draw an electrically meaningful schematic, or it can be used to draw a symbolic representation of the circuit entity. </p> <p> Whilst most objects on a <strong>page</strong> are graphic primitives, there are some which have a relation to the <strong>circuit</strong>'s electrical specification. </p> <ul> <li class="level1"><div class="li"> <strong>ConnSegments</strong> (or <strong>net</strong>s) represent connected electrical signals within the circuit represented.</div> <ul> <li class="level2"><div class="li"> A connectivity representation (<strong>netlist</strong>) can be built by considering the end-point positioning of these objects.</div> </li> <li class="level2"><div class="li"> <strong>ConnSegment</strong> is intended to be a generalisation of <strong>net</strong>s and <strong>bus</strong>es for the purpose of this diagram.</div> </li> </ul> </li> </ul> <ul> <li class="level1"><div class="li"> <strong>Pins</strong> represent a connection outside this circuit.</div> <ul> <li class="level2"><div class="li"> When constructing a netlist, coincidence of a <strong>ConnSegment</strong> end on these implies an electrical connection to that external port.</div> </li> <li class="level2"><div class="li"> Each <strong>pin</strong> (or group of pins?) represent an external electrical connection with this <strong>circuit</strong>.</div> </li> <li class="level2"><div class="li"> There is a necessary link between a <strong>pin</strong> and the circuit's <strong>Mport</strong> which it represents.</div> </li> </ul> </li> </ul> <ul> <li class="level1"><div class="li"> <strong>complex</strong> objects represent instantiating a sub-<strong>circuit</strong>, and will be linked to a specific <strong>instance</strong> structure.</div> <ul> <li class="level2"><div class="li"> Graphically, this means a <strong>symbolic</strong> representation of the instantiated circuit will be placed on the page.</div> </li> <li class="level2"><div class="li"> Nets ending co-incident with the <strong>pins</strong> of that embedded symbol represent electrical connectivity with the instantiated sub-<strong>circuit</strong> entity.</div> </li> </ul> </li> </ul> </div> <!-- EDIT1957 SECTION "Page" [3941-5460] --> <h1 class="sectionedit1958"><a name="brainstorms" id="brainstorms">Brainstorms</a></h1> <div class="level1"> <p> (from conversation on MSN/<acronym title="Internet Relay Chat">IRC</acronym> on 10th April 2007 – Peter Brett / Peter Clifton) </p> <ul> <li class="level1"><div class="li"> In order to do back annotation, need to be able to change the board part references for anywhere in the schematic. It then makes sense to dissociate the concepts of <strong>InstanceID</strong> and <strong>Board Reference</strong>, and use an <strong>override table</strong> that can override an attribute at any given path within the current <strong>circuit</strong> based on a path composed of <strong>InstanceID</strong>s. <strong>InstanceID</strong>s would be special-cased throughout libgeda as a means for uniquely identifying circuits and instances. An entry in the override table might have the form ”/id1/id2/id3:refdes:U3”</div> </li> </ul> <ul> <li class="level1"><div class="li"> It might be useful to allow nets to have attributes, for instance to specify minimum copper width and spacing for a net, independently from the attributes of net segments.</div> </li> </ul> <ul> <li class="level1"><div class="li"> The schematic editor needs to have sidebars for browsing hierarchy and inspecting attributes. This needs to include a way of seeing where the attributes have been inherited from.</div> </li> </ul> <ul> <li class="level1"><div class="li"> We need to do lazy netlisting, on a circuit-by-circuit basis – the netlists should only be combined into a flat netlist when required by a tool (and even then, most tools can potentially make good use of hierarchy information).</div> </li> </ul> <ul> <li class="level1"><div class="li"> In order to make finding objects by hierarchical path fast (e.g. to implement override tables discussed above) there needs to be a fast way of generating unique identifiers for objects (e.g. 32-bit ints) that can then be used as keys in hashtables.</div> </li> </ul> </div> <!-- EDIT1958 SECTION "Brainstorms" [5461-] --></body> </html>
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