The Structure and Syntax of the CadEnhance Symbol Description Language (SDL) is described here

Symbol Description Language Structure

The Symbol Description Language (SDL) was designed to be uber-efficient at describing schematic symbol construction, while still being simple to understand and easy to enter.

SDL KEY_WORDS and Constructs are Not case-sensitive. 

An SDL File is a collection of ordered SYMBOL_NAME_DEFINITIONS which enclose MATCH_STATEMENTS and SPACER_COMMANDS.

The number of symbols you create is generally greater than or equal to the number of SYMBOL_NAME_DEFINITIONS.

Moving pins from one symbol to another is generally a cut and paste operation to move MATCH_STATEMENTS in between a different SYMBOL_NAME_DEFINTION.

To add another symbol, you just add another SYMBOL_NAME_DEFINTION with a new name and add or move your MATCH_STATEMENTS between the start and end.

SYMBOL_NAME_DEFINITIONS, MATCH_STATEMENTS and SPACER_COMMANDS can also appear between the start and end of LOOP_DIRECTIVES

SDL also supports Simple VARIABLE_SUBSTITUTION commands.

SYMBOL_NAME_DEFINITION

A SYMBOL_NAME_DEFINITION is used to instruct partBuilder to start placing matching pins into a named symbol.

It has 2 parts, a beginning:

SymbolName=

and an end which is just the terminating semicolon.

';'

The SymbolName is the actual name you want to use for the symbol and it should not contain spaces

 in the simple sample file, the start of the first SYMBOL_NAME_DEFINITION  was

DRAM_ACTL_PINS=

That was followed by several MATCH_STATEMENTS  

and was terminated by the

';' 

character

It instructed partBuilder to create a Symbol named DRAM_ACTL_PINS as a place to add the pins matching all the MATCH_STATEMENTS that follow until the SYMBOL_NAME_DEFINITION is closed.

A SYMBOL_NAME_STATEMENT may often create more than one symbol if the number of pins that the MATCH_STATEMENTS assign to that symbol are greater than the current Configuration Setting of the SYMBOL_PIN_LIMIT.  For instance, a GROUND symbol definition often contains only one MATCH_STATEMENT to assign any pin matching GND to that symbol. If the part has 400 Ground pins and the SYMBOL_PIN_LIMIT is set to 100, it will create 4 SYMBOLS and create a new name for each of the extra symbols it creates (GROUND, GROUND_1, GROUND_2 and GROUND_3)

MATCH_STATEMENTS

MATCH_STATEMENTS are  what tell partBuilder which pins to place within the current symbol, what side to place them on  and any other modifier to enable creating special graphics or properites for the pins that match.

MATCH_STATEMENTS are built out of   LOCATOR, MODIFIER and PIN_MATCH elements

The simplest MATCH_STATEMENT only contains a LOCATOR and a PIN_MATCH, and is entered as

LOCATOR=>PIN_MATCH

The equal-Arrow "=>" separates the PIN_MATCH from the list of LOCATORS and MODIFIERS

MODIFIERS are added on the left hand side of the '=>' either before or after the LOCATOR.

For clarity and easier cut and paste in Excel, our examples will show the LOCATOR first.

MODIFIERS and LOCATORS are separated by the colon character ':' as follows;

LOCATOR:MODIFIER1:MODIFIER2:...MODIFIERn=>PIN_MATCH

There is no restriction on the number of valid MODIFIERS that can be included in  a MATCH_STATEMENT. 

It should be obvious that only one LOCATOR is used per MATCH_STATEMENT 

Some simple MATCH_STATEMENTS are provided in the table below to help get a feel for what they look like as you read more about the structure of them.

Examples of Simple MATCH_STATEMENTS.

LOCATOR Elements

The purpose of the LOCATOR element is to tell partBuilder what side of the symbol to place the matching pins on.

Part builder creates one list for each side  of the symbol, and as it sees a locator, it pushes the matching pins 

Valid Locators are mostly obvious, and are explained in the following table

MODIFIER Elements

Valid Modifiers are explained in the following table. Modifiers may be further broken down by partBuilder to impart extra information as shown

PIN_MATCH Elements

The PIN_MATCH Element is the string that PartBuilder uses to test all pins in the extracted pinData for a match. 

PIN_MATCHES may be entered as a simple string or with a wildcard.

PartBuilder treats all the PIN_MATCHES it extracts from the SDL as a Regular Expression. It actually converts the wildcard '*' internally to the '.*' used in Regular Expressions.

They may also be entered as a valid Perl Regular Expression.

PartBuilder treats all the PIN_MATCHES it extracts from the SDL as a Regular Expression. It actually converts the wildcard '*' internally to the '.*' used in Regular Expressions.

A Regular Expression is a pattern describing a certain amount of Text.  The Regular Expression can be very general or very restrictive.

In the simplest context, PartBuilder uses a regular expressions to determine if a Pin contains the PIN_MATCH pattern. 

If the PIN_MATCH  is entered as "DQ", PartBuilder will match any pin that Contains DQ anywhere in the pinname.

Excellent references for Regular Expressions exist on the web like the one at this link.

PartBuilder Bus-Enhanced Regular Expressions.

PartBuilder does some behind the scenes work to change the PIN_MATCH  Regular Expressions to enable  placing  bussed pins seamlessly

Its not truly necessary to understand this detail, but In a normal regular expression, the '[]' characters in the pattern match enclose a list of characters to match against

If you were comparing a list of pins dq7 dq6 dq5 dq4 dq3 dq2 dq1 and  dq0 using the regular Expression 'dq[0:7]' , the pattern would only match dq0 and dq7 (and funny enough dq:).

You could get more useful results with 'dq[0-7]' (because 0-7 inside the square brackets says to match any character between 0 and 7) but unfortunately that would not enforce the order of the pins. 

In order to work around this, when PartBuilder sees the 'DQ[0:7]' in a PIN_MATCH it  expands it to 8 seperate PIN_MATCHES DQ0, DQ1, DQ2... DQ7** which are then used as pattern matches.

It also maintains the order of the bits so that they will be added to the symbol in LSB→MSB order if you enter busName[0:7] or MSB→LSB order if you enter busName[7:0]. As described in the table below, it also appends whats called a zero-width-lookahead assertion at the end fo each  to insure that DQ18 doesn't match DQ1 but it would still allow a match of dq1_p

(**it also appends a  zero-width-lookahead assertion to each match to ensure that no other digits are following the ones we want so that DQ18 doesn't match DQ1) 

Examples of Useful PIN_MATCH Regular Expressions

Handling Pins that Match multiple PIN_MATCHES

It takes PartBuilder 2 passes to place matching pins into the proper symbols. It first goes through every pin_match and attaches a list of every MATCH_STATEMENT that each pin matches to the pin. It then makes a second pass, and chooses the MATCH_STATEMENT with the longest PIN_MATCH string to pick the proper MATCH_STATEMENT for that pin. 

Lets provide a simple example:

We have a fictional part with 100 pins named GND, 8 pins named SGND and 2 pins named GTH_RX_SGND and 2 named GTH_TX_SGND

We have the following 2  SYMBOL_NAME_DEFINTIONS in the SDL File

GND_SYM=

LEFT=>SGND

LEFT=>SPACER[1:0]

BOTH=>GND

;

GTH_BLOCK=

LEFT:dpair=>GTH_RX[7:0]_P

RIGHT:dpair=>GTH_RX[7:0]_N

!BSS+2

LEFT=>GTH_RX_SGND

RIGHT=>GTH_TX_SGND

;

Because of this 2 pass approach, the user does not need to concern themselves with what order a MATCH_STATEMENT is placed or what SYMBOL_DEFINTION it is placed in.

They do need to be aware that the 2 pass approach is necessary and that they need to assign more specific PIN_MATCHES to seperate Pins like the example that have common strings in them 

SPACER_COMMANDS

SPACER_COMMANDS allow the user to easily control spacing between groups of pins

There are 3 types:

• SINGLE_SPACERS:
  • LOCATOR=>SPACER,
• MULTIPLE_SPACERS:
  
  • LOCATOR=>SPACER[5:0]
• and SPACER_DIRECTIVES:
  • !BALANCE_SYM_SIDES+n (or !BSS+n)

The first 2 resemble the MATCH_STATEMENTS pretty closely and use the LEFT, RIGHT, TOP and BOTTOM LOCATOR commands.

The !BALANCE_SYM_SIDES directive is used to start a new section in the same symbol without having to keep track of the number of pins you have been adding on the sides of your symbols.

For instance if you have 3 pins on the left and 8 pins on the right, The BALANCE_SYM_SIDES+2 directive would add 5 spacer pins on the left to Balance it with the right side, and then add 2 more spacers on each side.

LOOP_DIRECTIVES AND VARIABLE SUBSTITUTION

SDL LOOP_DIRECTIVES and VARIABLE SUBSTITUTION greatly increase the efficiency of creating parts that contain multiple similar interfaces like a microprocessor with 2 DRAM busses or an FPGA with multiple IO Banks with the same number and types of pins.  They can also be used to quickly break up busses into nicely structured sub-busses 

The Expanded SDL File

PartBuilder first scans the input SDL file to see if it contains  LOOP _DIRECTIVES or Variable Substitution. If it finds any, it creates a new, expanded version of the input SDL file which it saves to the local directory and then uses for the pin to symbol assigment step. The expanded file has all the LOOP_DIRECTIVES and VARIABLE_SUB_DIRECTIVES removed.  The LOOP_DIRECTIVES cause the expander to copy ranges of lines multiple times in the expanded file with the LOOP variables substituted.

One benefit of this approach is it allows the user to clearly see how the loops were expanded, and possibly catch any unintended consequences of the loops. While the user is encouraged to examine the expanded SDL File, They  should be careful not to edit it, as any changes they make to that file will be overwritten the next time PartBuilder reads and expands the input SDL file.

VARIABLE Value Assignment and Substitution

The user can use variables within Loops or just globally change a of a set of PIN_MATCHES in some MATCH_STATEMENTS that they cut and paste.

VARIABLES can be substituted anywhere in the SDL including in Comments, SYMBOL_NAME_DEFINITIONS and MATCH_STATEMENTS.

A Variable is assigned with the following statement:

`LET VAR_NAME=VALUE

The VAR_NAME cannot contain spaces, but it can consist of any other characters except the backtick and the equal sign.

The VALUE can be a number or a string or a mix of numbers and characters and spaces.

To have PartBuilder substitute the current Value of a variable in the SDL, the VARIABLE is prepended with a backtick and suffixed with 2 colons like:

`VAR_NAME:: 

Quick Example:

`LET SYM=3

RX_SYMBOL_`SYM::=

`LET A=[5:0]

LEFT:dpair=>RX`A::_P

RIGHT:dpair=>TX`A::_P

`LET A=[11:6]

LEFT:dpair=>RX`A::_P

RIGHT:dpair=>TX`A::_P

RX_SYMBOL_3=

LEFT:dpair=>RX[5:0]_P

RIGHT:dpair=>TX[5:0]_P

LEFT:dpair=>RX[11:6]_P

RIGHT:dpair=>TX[11:6]_P

LOOP_DIRECTIVES

There are 4 main types of LOOP_DIRECTIVES

Each One must  start at the beginning of a line with the backtick ` character to tell PartBuilder that this is a special line

When PartBuilder Expands the Input SDL file upon seeing a LOOP_DIRECTIVE, it is making a copy of the lines between

the `FOR and `END_FOR and substituting in the LOOP_VARIABLE as it copies

Lets show a simple example before we look at the technical parts

`FOR B in (1..2,15..16)
IO_BANK_`B::=
left:dpair=>clk`B::_i_p
right:dpair=>clk`B::_o_p
!BSS+2
left=>BUS`B::_RX_DQ[7:0]
right=>BUS`B::_TX_DQ[7:0]
;
`ENDFOR

#This File has been expanded by partBuilder from the input file:symbolOrder.txt 
#Do not edit it as any changes you make will be lost the next time partBuilder
#runs the map_pins_to_symbols step


IO_BANK_1=
left:dpair=>clk1_i_p
right:dpair=>clk1_o_p
!BSS+2
left=>BUS1_RX_DQ[7:0]
right=>BUS1_TX_DQ[7:0]
;
IO_BANK_2=
left:dpair=>clk2_i_p
right:dpair=>clk2_o_p
!BSS+2
left=>BUS2_RX_DQ[7:0]
right=>BUS2_TX_DQ[7:0]
;
IO_BANK_15=
left:dpair=>clk15_i_p
right:dpair=>clk15_o_p
!BSS+2
left=>BUS15_RX_DQ[7:0]
right=>BUS15_TX_DQ[7:0]
;

IO_BANK_16=
left:dpair=>clk16_i_p
right:dpair=>clk16_o_p
!BSS+2
left=>BUS16_RX_DQ[7:0]
right=>BUS16_TX_DQ[7:0]
;

ITERATVE_LOOP:

`FOR (LOOP_VAR=START_VAL; LOOP_VAR COMP_OPERATOR END_VAL; LOOPVAR INC_DEC_OPERATOR)

SDL_STATEMENTS (some with `VARNAME:: for substitution )

`END_FOR (or `ENDFOR) 

The first is similar to iterative loops most commonly encountered in programming languages like C and Perl. 

With the advent of the other loop structures, this one has become less useful for building symbols, but can still be used to perform some

simple substitutions to avoid having to add large 

`FOR LOOP_VAR IN (LIST_OF_VALUES)

SDL_STATEMENTS (some with `VARNAME:: for LOOP_VARIABLE substitution )

`END_FOR (or `ENDFOR)

`FOR LOOP_VAR_LIST IN (LIST_OF_VALUES) 

SDL_STATEMENTS (some with `VARNAME:: for substitution )

`END_FOR (or `ENDFOR)

`REPEAT n LOOP

SDL_STATEMENTS (some with BUSSED INC_DEC operators)

`END_REPEAT