Differences

This shows you the differences between two versions of the page.

--- etc:users:jcmvbkbc:isl [2010/07/13 01:05] – + pack/unpack signatures jcmvbkbc
+++ etc:users:jcmvbkbc:isl [2016/08/08 20:53] (current) – ↷ Page moved from users:jcmvbkbc:isl to etc:users:jcmvbkbc:isl kel
@@ Line 3: / Line 3: @@
 [[http://jcmvbkbc.spb.ru/git/?p=dumb/isl.git;a=summary | Git repo (http)]]
-===== Output files structure =====
+[[http://jcmvbkbc.spb.ru:8000/isle/trac | Project tracker]]
+===== Orthogonal aspects =====
+Orthogonal aspects must be decoupled to the maximal possible extent:
+  * output language
+  * output file structure
+  * user data structures and field names
+  * memory allocation
+===== Output files structure (C) =====
 .h
@@ Line 26: / Line 37: @@
 pack_<interface name>(
     SignalType signal, /* signal type */
-    Param1_t_uunion *p1, /* only present when interface has explicit header */
+    Param1_t_uunion *p1, /* only present when interface has explicit header with non-autogenerated fields */
-    Param2_t_uunion *p2, /* signal data */
+    Param2_t_uunion *p2, /* only present when interface has explicit trailer */
-    Param3_t_uunion *p3, /* only present when interface has explicit trailer */
+    Param3_t_uunion *p3, /* signal data */
     <pdu arg type> pdu, /* pdu output buffer */
     <pdu size arg type> sz /* pdu buffer size */
@@ Line 40: / Line 51: @@
     <pdu size arg type> sz, /* pdu buffer size */
     SignalType *signal, /* signal type */
-    Param1_t_uunion **p1, /* only present when interface has explicit header */
+    Param1_t_uunion **p1, /* only present when interface has explicit header with non-autogenerated fields */
-    Param2_t_uunion **p2, /* signal data */
+    Param2_t_uunion **p2, /* only present when interface has explicit trailer */
-    Param3_t_uunion **p3, /* only present when interface has explicit trailer */
+    Param3_t_uunion **p3, /* signal data */
 );
 </code>
-c
+When the header is absent Param1 corresponds to the trailer. If there's no trailer, its parameter number corresponds to the signal data.
+Interfaces visible from root package, not referenced from other interfaces visible from root package get translated to pack/unpack.
+===== Decoding context =====
+  * basic part:
+    * bit stream location (byte offset, bit offset)
+    * memory allocation context
+  * custom part:
+    * internal variables (managed by 'internal variable assignment' clause)
+===== Field decoder function signature =====
+<code>
+<unpack return type>
+unpack_<field name>(
+  <decoding context type> * dc, /* data location, updated during unpacking */
+  <field type> * p /* filled in by this unpack */
+);
+</code>
+===== Union member naming =====
+<code>
+Header:
+Param1_t_uunion
+{
+    <interface name>_t <interface name>;
+};
+Trailer:
+Param2_t_uunion
+{
+    <interface name>_trailer_t <interface name>_trailer;
+};
+Signal:
+Param3_t_uunion
+{
+    <message name>_t <message name>;
+};
+</code>
+===== Message type =====
+  * when interface header doesn't have explicit messagetype filed, default 'messagetype : 1 byte' field is added to the tail of the interface header;
+===== Mandatory/optional sections =====
+Mandatory_tagged and mandatory_unordered fields need iei. iei values for mandatory_unordered must be unique in each mandatory_unordered section (?).
+  * fields in mandatory section go to binary and back as is;
+  * fields in mandatory_tagged section are prepended by their respective iei when coded. When decoded presence of correct iei is verified;
+  * fields in mandatory_unordered section are coded like mandatory_tagged. When decoded, they may go in arbitrary order; iei not listed in current mandatory_unordered group terminates decoding of the current group (mt);
+All optional fields need iei, which must be unique in each optional section (?).
+  * fields in optional section have satellite <name>Present field in decoded struct; they're encoded and decoded as mandatory_unordered;
+  * fields in optional_ordered section imply <name>Present field in decoded struct; they're encoded and decoded as mandatory_tagged;
+  * fields in optional_repeated form standard list with First, Last, IsAssigned and Length fields; they're encoded in order and decoded in any order;
+All sections may interleave, however mt does not diagnose possible ambiguities when first byte of mandatory field may be valid iei. Such diagnostic would be good.
+Consecutive mandatory_unordered, optional and optional_repeated sections form a cluster where order of fields is insignificant.
+Cluster decoding runs for the length of the current scope. Initially this length is determined by PDU length and may be further narrowed down by the message/field own length.
+Unknown iei triggers TLV recovery mechanism: mt reads 16 (?) bits after iei and use them as length of unknown iei field.
+Only mandatory fields may have LengthRestriction > 1.
+===== Derived interfaces =====
+  * if derivation is by inversion, another interface is created and parent's pack-only messages become its unpack-only and vice versa;
+  * if derivation is by narrowing, another interface is created and extra messages are removed from there;
+  * derived interface is always represented by the DerivedInterface class;
+===== Validation constraints =====
+==== Interface ====
+  * symbols in pack/unpack sections are visible and refer to messages or interfaces;
+  * every pack/unpack message has corresponding messagetype;
+  * header and trailer follow the rules for fields;
+  * message types are all different;
+==== Field/Message ====
+  * types of subfields are visible, parameterized types has required arguments;
+  * field names are unique in each field contents scope;
+  * no cyclic dependencies of fields/messages (mt does not allow it);
+    * however, even with the current naming rules there may be cyclic dependencies in optional_repeated parts and inside case constructs;
+    * generally every optional parts and case content may have cyclic dependencies;
+==== Constants ====
+  * expression in constant's definition may only refer to other constants and literals;
+  * constants may not have recursive definition;
+===== Language features =====
+==== Definitions ====
+  * children: first level of contained objects;
+  * descendants: all levels of contained objects;
+  * parent: direct container of the object;
+  * ancestor: any indirect container of the object;
+  * sibling: another child of the object's parent;
+==== Namespaces ====
+Namespace is set of object types and the set of rules, that describe how objects of the same name interact in certain scope.
+  * packages (P): last definition is effective in the package scope;
+  * constants, fields, messages, interfaces (CFMI): must be unique in visible scope;
+  * subfields: subfields must be unique in the field contents scope;
+==== Scopes ====
+  * package: children of the package object;
+  * natural scope: package + package scopes of ancestors;
+  * visible scope: package + visible scopes of used packages + visible scopes of ancestors;
+  * field/message/interface header/interface pack-unpack/interface trailer;
+  * field contents: each level of nested braces in field/message/interface (header and trailer parts) definition;
+==== Packages ====
+  * package nesting is unrestricted;
+  * use does not affect P namespace;
+    * if A contains B, B contains C and A use B, one cannot write A use C;
+  * use adds visible scope of the used package to the current visible scope in CFMI namespace;
+    * use directive in transitive, i.e. A use B and B use C means A use C;
+  * only package from natural scope may be used, i.e. package may use only children of its ancestors and its children;
+  * original parser has issues with packages:
+    * it treats root package differently than named packages;
+    * sibling packages don't merge and don't collide, one defined later is effective, others are ignored;
+===== Naming for C output =====
+There are two generic rules:
+  * type names are generated with suffix '_t' added to the base name;
+  * when there's only one subfield in the field it gets reduced, like there's no container structure. Subfield gets basic name of its container;
+    * 'one subfield' is literally one subfield. Presence of the special-purpose subfields that would not get into the structure or constant fillers cancels reduction.
+==== Field/message type ====
+<C field type> = <Field name>_t
+Ex:
+<code>
+field A
+{
+...
+}
+typedef struct {...} A_t;
+</code>
+==== Enum ====
+Enum type:
+  * if this is the only subfield (so that reduction takes place), <C enum type> = <C field type>;
+  * otherwise <C enum type> = <Field name>_<subfield name>_t;
+<C Enum value> = <C enum type>_<Enum value>
+Ex:
+<code>
+field A
+{
+    a : 1 byte { V1 = 1, V2 = 2 };
+}
+field B
+{
+    a : 1 byte { V1 = 1, V2 = 2 },
+    b : 1 byte { V1 = 1, V2 = 2 };
+}
+typedef enum { A_t_V1 = 1, A_t_V2 = 2 } A_t; // reduction
+typedef enum { B_a_t_V1 = 1, B_a_t_V2 = 2 } B_a_t;
+</code>
+==== Case ====
+  * <C choice type> = <C container type>_<tag subfield name>_choice{index, if > 1}
+  * <C choice type_t> = <C choice type>_t
+  * case labels (only literals, tag field enum values or global constants may be used):
+    * for numeric labels <C case name> = case<case label>
+    * for enum labels <C case name> = <enum label>
+Choice is always represented by the following structure:
+<code>
+struct <C choice type_t> { <C choice type_t>_tag_enum _tag; <C choice type_t>_uunion U; };
+typedef enum { <C choice type_t>_tag_enum_<C case name>, ... } <C choice type_t>_tag_enum;
+union <C choice type_t>_uunion { <C choice type>_<C case name>_t <C case name>; ... };
+</code>
+Ex: see case.pdu
+===== Schedule =====
+  * finalize naming for the following items:
+    * exported constants;
+    * cases;
+    * ranges;
+    * arrays of primitive types;
+    * strings;
+    * interfaces, derived and nested;
+    * ?
+  * separate compiler frontend and backend;
+  * implement validators;
+  * implement pack/unpack;
+    * interfaces;
+    * optional/mandatory;
+    * alignment;
+    * type instantiation and deep referencing;
+  * test;
+  * presentation;