# x65 6502 Macro Assembler in a single c++ file using the struse single file text parsing library. Supports most syntaxes. x65 was recently named Asm6502 but was renamed because Asm6502 is too generic, x65 has no particular meaning. Every assembler seems to add or change its own quirks to the 6502 syntax. This implementation aims to support all of them at once as long as there is no contradiction. To keep up with this trend x65 is adding the following features to the mix: * Full expression evaluation everywhere values are used: [Expressions](#expressions) * Basic relative sections and linking. * C style scoping within '{' and '}': [Scopes](#scopes) * Reassignment of labels. This means there is no error if you declare the same label twice, but on the other hand you can do things like label = label + 2. * [Local labels](#labels) can be defined in a number of ways, such as leading period (.label) or leading at-sign (@label) or terminating dollar sign (label$). * [Directives](#directives) support both with and without leading period. * Labels don't need to end with colon, but they can. * No indentation required for instructions, meaning that labels can't be mnemonics, macros or directives. * Conditional assembly with #if/#ifdef/#else etc. * As far as achievable, support the syntax of other 6502 assemblers (Merlin syntax now requires command line argument). In summary, if you are familiar with any 6502 assembler syntax you should feel at home with x65. If you're familiar with C programming expressions you should be familiar with '{', '}' scoping and complex expressions. There are no hard limits on binary size so if the address exceeds $ffff it will just wrap around to $0000. I'm not sure about the best way to handle that or if it really is a problem. There is a sublime package for coding/building in Sublime Text 3 in the *sublime* subfolder. ## Prerequisite x65.cpp requires struse.h which is a single file text parsing library that can be retrieved from https://github.com/Sakrac/struse. ### References * [6502 opcodes](http://www.6502.org/tutorials/6502opcodes.html) * [6502 opcode grid](http://www.llx.com/~nparker/a2/opcodes.html) * [Codebase64 CPU section](http://codebase64.org/doku.php?id=base:6502_6510_coding) ## Command Line Options The command line options specifies the source file, the destination file and what type of file to generate, such as c64 or apple II dos 3.3 or binary or an x65 specific object file. You can also generate a disassembly listing with inline source code or dump the available set of opcodes as a source file. The command line can also set labels for conditional assembly to allow for distinguishing debug builds from shippable builds. Typical command line ([*] = optional): ``` x65 [-DLabel] [-iIncDir] (source.s) (dest.prg) [-lst[=file.lst]] [-opcodes[=file.s]] [-sym dest.sym] [-vice dest.vs] [-obj]/[-c64]/[-bin]/[-a2b] [-merlin] [-endm] ``` **Usage** x65 filename.s code.prg [options] * -i(path): Add include path * -D(label)[=(value)]: Define a label with an optional value (otherwise defined as 1) * -cpu=6502/65c02/65c02wdc/65816: assemble with opcodes for a different cpu * -obj (file.x65): generate object file for later linking * -bin: Raw binary * -c64: Include load address (default) * -a2b: Apple II Dos 3.3 Binary * -sym (file.sym): symbol file * -merlin: use Merlin syntax * -lst / -lst=(file.lst): generate disassembly text from result (file or stdout) * -opcodes / -opcodes=(file.s): dump all available opcodes (file or stdout) * -sect: display sections loaded and built * -vice (file.vs): export a vice symbol file * -endm: macros end with endm or endmacro instead of scoped ('{' - '}') ## Features * **Code** * **Linking** * **Comments** * **Labels** * **Directives** * **Macros** * **Expressions** ### Code Code is any valid mnemonic/opcode and addressing mode. At the moment only one opcode per line is assembled. ### Linking In order to manage more complex projects linking multiple assembled object files is desirable. x65 implements this by saving the state of the assembler as an 'object' file that can be appended into the assembling of another source file with the [INCOBJ](#incobj) directive. To control the final layout of code and data a [SECTION](#section) directive can be used to specify the kind of data that is declared. As a result of the custom object file, fixed address sections (ORG) can be declared within x65 object files. x65 does not support any other type of object file, and the x65 object file format may change throughout development of x65. ### Comments Comments are currently line based and both ';' and '//' are accepted as delimiters. ### Expressions Anywhere a number can be entered it can also be interpreted as a full expression, for example: ``` Get123: bytes Get1-*, Get2-*, Get3-* Get1: lda #1 rts Get2: lda #2 rts Get3: lda #3 rts ``` Would yield 3 bytes where the address of a label can be calculated by taking the address of the byte plus the value of the byte. ### Labels Labels come in two flavors: **Addresses** (PC based) or **Values** (Evaluated from an expression). An address label is simply placed somewhere in code and a value label is followed by '**=**' and an expression. All labels are rewritable so it is fine to do things like NumInstance = NumInstance+1. Value assignments can be prefixed with '.const' or '.label' but is not required to be prefixed by anything, the CONST keyword should cause an error if the label is modified in the same source file. *Local labels* exist inbetween *global labels* and gets discarded whenever a new global label is added. The syntax for local labels are one of: prefix with period, at-sign, exclamation mark or suffix with $, as in: **.local** or **!local** or **@local** or **local$**. Both value labels and address labels can be local labels. ``` Function: ; global label ldx #32 .local_label ; local label dex bpl .local_label rts Next_Function: ; next global label, the local label above is now erased. rts ``` ### Directives Directives are assembler commands that control the code generation but that does not generate code by itself. Some assemblers prefix directives with a period (.org instead of org) so a leading period is accepted but not required for directives. * [**CPU**](#cpu) Set the CPU to assemble for. * [**ORG**](#org) (same as **PC**): Set the current compiling address. * [**LOAD**](#load) Set the load address for binary formats that support it. * [**SECTION**](#section) Start a relative section * [**LINK**](#link) Link a relative section at this address * [**XDEF**](#xdef) Make a label available globally * [**INCOBJ**](#incobj) Include an object file (.x65) to this file * [**EXPORT**](#export) Save out additional binary files with argument appended to filename * [**ALIGN**](#align) Align the address to a multiple by filling with 0s * [**MACRO**](#macro) Declare a macro * [**EVAL**](#eval) Log an expression during assembly. * [**BYTES**](#bytes) Insert comma separated bytes at this address (same as **BYTE** or **DC.B**) * [**WORDS**](#words) Insert comma separated 16 bit values at this address (same as **WORD** or **DC.W**) * [**TEXT**](#text) Insert text at this address * [**INCLUDE**](#include) Include another source file and assemble at this address * [**INCBIN**](#incbin) Include a binary file at this address * [**CONST**](#const) Assign a value to a label and make it constant (error if reassigned with other value) * [**LABEL**](#label) Decorative directive to assign an expression to a label * [**INCSYM**](#incsym) Include a symbol file with an optional set of wanted symbols. * [**POOL**](#pool) Add a label pool for temporary address labels * [**#IF / #ELSE / #IFDEF / #ELIF / #ENDIF**](#conditional) Conditional assembly * [**STRUCT**](#struct) Hierarchical data structures (dot separated sub structures) * [**REPT**](#rept) Repeat a scoped block of code a number of times. * [**INCDIR**](#incdir) Add a directory to look for binary and text include files in. * [**65816**](#65816) A16/A8/I16/I8 Directives to control the immediate mode size * [**MERLIN**](#merlin) A variety of directives and label rules to support Merlin assembler sources **CPU** Set the CPU to assemble for. This can be updated throughout the source file as needed. **PROCESSOR** is also accepted as an alias. ``` CPU 65816 ``` **ORG** ``` org $2000 (or pc $2000) ``` Start a section with a fixed addresss. Note that source files with fixed address sections can be exported to object files and will be placed at their location in the final binary output when loaded with **INCOBJ**. **SECTION** ``` section Code Start: lda #Data sta $ff rts section BSS Data: byte 1,2,3,4 ``` Starts a relative section. Relative sections require a name and sections that share the same name will be linked sequentially. The labels will be evaluated at link time. Sections can be aligned by adding a comma separated argument: ``` section Data,$100 ``` Sections can be names and assigned a fixed address by immediately following with an ORG directive ``` section Code org $4000 ``` If there is any code or data between the SECTION and ORG directives the ORG directive will begin a new section. The primary purpose of relative sections (sections that are not assembled at a fixed address) is to generate object files (.x65) that can be referenced from a linking source file by using **INCOBJ** and assigned an address at that point using the **LINK** directive. Object files can mix and match relative and fixed address sections and only the relative sections need to be linked using the **LINK** directive. **XDEF** Used in files assembled to object files to share a label globally. All labels that are not xdef'd are still processed but protected so that other objects can use the same label name without colliding. **XDEF ** must be specified before the label is defined, such as at the top of the file. Non-xdef'd labels are kept private to the object file for the purpose of late evaluations that may refer to them, and those labels should also show up in .sym and vice files. ``` XDEF InitBobs InitBobs: rts ``` **INCOBJ** Include an object file for linking into this file. In order to include the object code into a binary the sections from the object file must be referenced using the *LINK* directive. **LINK** Link a set of relative sections (sharing the same name) at this address The following lines will place all sections named Code sequentially at location $1000, followed by all sections named BSS: ``` org $1000 link Code link BSS ``` There is currently object file support (use -obj argument to generate), the recommended file extension for object files is .x65. In order to access symbols from object file code use XDEF prior to declaring a label within the object. **LOAD** ``` load $2000 ``` For c64 .prg files this prefixes the binary file with this address. **EXPORT** Allows saving multiple binary files (prg, a2b, bin, etc.) from a single source file build ``` section gamecode_level1 export _level1 ``` will export the section "gamecode_level1" to (output_file)_level1.prg while other sections would be grouped together into (output_file).prg. This allows a single linking source to combine multiple loads overlapping the same memory area ending up in separate files. **ALIGN** ``` align $100 ``` Add bytes of 0 up to the next address divisible by the alignment. If the section is a fixed address (using an ORG directive) align will be applied at the location it was specified, but if the section is relative (using the SECTION directive) the alignment will apply to the start of the section. **MACRO** See the '[Macro](#macro)' section below **EVAL** Example: ``` eval Current PC: * ``` Might yield the following in stdout: ``` Eval (15): Current PC : "*" = $2010 ``` When eval is encountered on a line print out "EVAL (\) \: \ = \" to stdout. This can be useful to see the size of things or debugging expressions. **BYTES** Adds the comma separated values on the current line to the assembled output, for example ``` RandomBytes: bytes NumRandomBytes { bytes 13,1,7,19,32 NumRandomBytes = * - ! } ``` **byte** or **dc.b** are also recognized. **WORDS** Adds comma separated 16 bit values similar to how **BYTES** work. **word** or **dc.w** are also recognized. **TEXT** Copies the string in quotes on the same line. The plan is to do a petscii conversion step. Use the modifier 'petscii' or 'petscii_shifted' to convert alphabetic characters to range. Example: ``` text petscii_shifted "This might work" ``` **INCLUDE** Include another source file. This should also work with .sym files to import labels from another build. The plan is for x65 to export .sym files as well. Example: ``` include "wizfx.s" ``` **INCBIN** Include binary data from a file, this inserts the binary data at the current address. Example: ``` incbin "wizfx.gfx" ``` **CONST** Prefix a label assignment with 'const' or '.const' to cause an error if the label gets reassigned. ``` const zpData = $fe ``` **LABEL** Decorative directive to assign an expression to a label, label assignments are followed by '=' and an expression. These two assignments do the same thing (with different values): ``` label zpDest = $fc zpDest = $fa ``` **INCSYM** Include a symbol file with an optional set of wanted symbols. Open a symbol file and extract a set of symbols, or all symbols if no set was specified. Local labels will be discarded if possible. ``` incsym Part1_Init, Part1_Update, Part1_Exit "part1.sym" ``` **POOL** Add a label pool for temporary address labels. This is similar to how stack frame variables are assigned in C. A label pool is a mini stack of addresses that can be assigned as temporary labels with a scope ('{' and '}'). This can be handy for large functions trying to minimize use of zero page addresses, the function can declare a range (or set of ranges) of available zero page addresses and labels can be assigned within a scope and be deleted on scope closure. The format of a label pool is: "pool start-end, start-end" and labels can then be allocated from that range by ' **STRUCT** Hierarchical data structures (dot separated sub structures) Structs helps define complex data types, there are two basic types to define struct members, and as long as a struct is declared it can be used as a member type of another struct. The result of a struct is that each member is an offset from the start of the data block in memory. Each substruct is referenced by separating the struct names with dots. Example: ``` struct MyStruct { byte count word pointer } struct TwoThings { MyStruct thing_one MyStruct thing_two } struct Mixed { word banana TwoThings things } Eval Mixed.things Eval Mixed.things.thing_two Eval Mixed.things.thing_two.pointer Eval Mixed.things.thing_one.count ``` results in the output: ``` EVAL(16): "Mixed.things" = $2 EVAL(27): "Mixed.things.thing_two" = $5 EVAL(28): "Mixed.things.thing_two.pointer" = $6 EVAL(29): "Mixed.things.thing_one.count" = $2 ``` **REPT** Repeat a scoped block of code a number of times. The syntax is rept \ { \ }. Example: ``` columns = 40 rows = 25 screen_col = $400 height_buf = $1000 rept columns { screen_addr = screen_col ldx height_buf dest = screen_addr remainder = 3 rept (rows+remainder)/4 { stx dest dest = dest + 4*40 } rept 3 { inx remainder = remainder-1 screen_addr = screen_addr + 40 dest = screen_addr rept (rows+remainder)/4 { stx dest dest = dest + 4*40 } } screen_col = screen_col+1 height_buf = height_buf+1 } ``` **INCDIR** Adds a folder to search for INCLUDE, INCBIN, etc. files in ###**65816** * **A16** Set immediate mode for accumulator to be 16 bits * **A8** Set immediate mode for accumulator to be 8 bits * **I16** Set immediate mode for index registers to be 16 bits. **XY16** is also accepted. * **I8** Set immediate mode for index registers to be 8 bits. **XY8** is also accepted. The accumulator and index register mode will be reset to 8 bits if the CPU is switched to something other than 65816. An alternative method is to add .b/.w to immediate mode instructions that support 16 bit modes such as: ``` ora.b #$21 ora.w #$2322 ``` This alleviates some confusion about which mode a certain line might be assembled for when looking at source code. Similarly for instructions that accept 3 byte addresses (bank + address) adding .l instructs the assembler to choose a bank address: ``` and.l $222120 and.l $222120,x jsr.l $203212 ``` Although if six hexadecimal digits are specified the bank + address instruction will be assembled without decoration. Alternatively Merlin simply adds an 'l' to the instruction: ``` andl $222120 andl $222120,x jsrl $203212 ``` x65 Labels are not restricted to 16 bits, the bank byte can be extracted from a label with the '^' operator: ``` lda #^label ``` ###**MERLIN** A variety of directives and label rules to support Merlin assembler sources. Merlin syntax is supported in x65 since there is historic relevance and readily available publicly release source. * [Pinball Construction Set source](https://github.com/billbudge/PCS_AppleII) (Bill Budge) * [Prince of Persia source](https://github.com/jmechner/Prince-of-Persia-Apple-II) (Jordan Mechner) To enable Merlin 8.16 syntax use the '-merlin' command line argument. Where it causes no harm, Merlin directives are supported for non-merlin mode. *LABELS* ]label means mutable address label, also does not seem to invalidate local labels. :label is perfectly valid, currently treating as a local variable labels can include '?' Merlin labels are not allowed to include '.' as period means logical or in merlin, which also means that enums and structs are not supported when assembling with merlin syntax. *Expressions* Merlin may not process expressions (probably left to right, parenthesis not allowed) the same as x65 but given that it wouldn't be intuitive to read the code that way, there are probably very few cases where this would be an issue. **XC** Change processor. The first instance of XC will switch from 6502 to 65C02, the second switches from 65C02 to 65816. To return to 6502 use **XC OFF**. To go directly to 65816 **XC XC** is supported. **MX** MX sets the immediate mode accumulator instruction size, it takes a number and uses the lowest two bits. Bit 0 applies to index registers (x, y) where 0 means 8 bits and 1 means 16 bits, bit 1 applies to the accumulator. Normally it is specified in binary using the '%' prefix. ``` MX %11 ``` **LUP** LUP is Merlingo for loop. The lines following the LUP directive to the keyword --^ are repeated the number of times that follows LUP. **MAC** MAC is short for Macro. Merlin macros are defined on line inbetween MAC and <<< or EOM. Macro arguments are listed on the same line as MAC and the macro identifier is the label preceeding the MAC directive on the same line. **EJECT** An old assembler directive that does not affect the assembler but if printed would insert a page break at that point. **DS** Define section, followed by a number of bytes. If number is positive insert this amount of 0 bytes, if negative, reduce the current PC. **DUM**, **DEND** Dummy section, this will not write any opcodes or data to the binary output but all code and data will increment the PC addres up to the point of DEND. **PUT** A variation of **INCLUDE** that applies an oddball set of filename rules. These rules apply to **INCLUDE** as well just in case they make sense. **USR** In Merlin USR calls a function at a fixed address in memory, x65 safely avoids this. If there is a requirement for a user defined macro you've got the source code to do it in. **SAV** SAV causes Merlin to save the result it has generated so far, which is somewhat similar to the [EXPORT](#export) directive. If the SAV name is different than the source name the section will have a different EXPORT name appended and exported to a separate binary file. ## Expression syntax Expressions contain values, such as labels or raw numbers and operators including +, -, \*, /, & (and), | (or), ^ (eor), << (shift left), >> (shift right) similar to how expressions work in C. Parenthesis are supported for managing order of operations where C style precedence needs to be overridden. In addition there are some special characters supported: * \*: Current address (PC). This conflicts with the use of \* as multiply so multiply will be interpreted only after a value or right parenthesis * <: If less than is not followed by another '<' in an expression this evaluates to the low byte of a value (and $ff) * >: If greater than is not followed by another '>' in an expression this evaluates to the high byte of a value (>>8) * ^: Inbetween two values '^' is an eor operation, as a prefix to values it extracts the bank byte (v>>24). * !: Start of scope (use like an address label in expression) * %: First address after scope (use like an address label in expression) * $: Precedes hexadecimal value * %: If immediately followed by '0' or '1' this is a binary value and not scope closure address Example: ``` lda #(((>SCREEN_MATRIX)&$3c)*4)+8 sta $d018 ``` ## Macros A macro can be defined by the using the directive macro and includes the line within the following scope: Example: ``` macro ShiftLeftA(Source) { rol Source rol A } ``` The macro will be instantiated anytime the macro name is encountered: ``` lda #0 ShiftLeftA($a0) ``` The parameter field is optional for both the macro declaration and instantiation, if there is a parameter in the declaration but not in the instantiation the parameter will be removed from the macro. If there are no parameters in the declaration the parenthesis can be omitted and will be slightly more efficient to assemble, as in: ``` .macro GetBit { asl bne % jsr GetByte } ``` Alternative syntax for macros: To support the syntax of other assemblers macro parameters can also be defined through space separated arguments: ``` macro loop_end op lbl { op bne lbl } ldx #4 { sta buf,x loop_end dex ! } ``` Other assemblers use a directive to end macros rather than a scope (inbetween { and }). This is supported by adding '-endm' to the command line: ``` macro ShiftLeftA source rol source asl endm ``` As long as the macro end directive starts with endm it will be accepted, so endmacro will work as well. Currently macros with parameters use search and replace without checking if the parameter is a whole word, the plan is to fix this. ## Scopes Scopes are lines inbetween '{' and '}' including macros. The purpose of scopes is to reduce the need for local labels and the scopes nest just like C code to support function level and loops and inner loop scoping. '!' is a label that is the first address of the scope and '%' the first address after the scope. This means you can write ``` { lda #0 ldx #8 { sta Label,x dex bpl ! } } ``` to construct a loop without adding a label. ##Examples Using scoping to avoid local labels ``` ; set zpTextPtr to a memory location with text ; return: y is the offset to the first space. ; (y==0 means either first is space or not found.) FindFirstSpace ldy #0 { lda (zpTextPtr),y cmp #$20 beq % ; found, exit iny bne ! ; not found, keep searching } rts ``` ### Development Status Currently the assembler is in an early revision and while features are tested individually it is fairly certain that untested combinations of features will indicate flaws and certain features are not in a complete state. **TODO** * Macro parameters should replace only whole words instead of any substring * Add 'import' directive as a catch-all include/incbin/etc. alternative * irp (indefinite repeat) * boolean operators (==, <, >, etc.) for better conditional expressions **FIXED** * 65816 * 65C02 enabled through directives (PROCESSOR/CPU/XC) * 65c02 (currently only through command line, not as a directive) * Now accepts negative numbers, Merlin LUP and MAC keyword support * Merlin syntax fixes (no '!' in labels, don't skip ':' if first character of label), symbol file fix for included object files with resolved labels for relative sections. List output won't disassemble lines that wasn't built from source code. * Export full memory of fixed sections instead of a single section * Option to source disasm output and option to dump all opcodes as a source file for tests * Object file format so sections can be saved for later linking * Added relative sections and relocatable references * Added Apple II Dos 3.3 Binary Executable output (-a2b) * Added more Merlin rules * Added directives from older assemblers * Added ENUM, sharing some functionality with STRUCT * Added INCDIR and command line options * [REPT](#rept) * fixed a flaw in expressions that ignored the next operator after raw hex values if no whitespace * expressions now handles high byte/low byte (\>, \<) as RPN tokens and not special cased. * structs * ifdef / if / elif / else / endif conditional code generation directives * Label Pools added * Bracket scoping closure ('}') cleans up local variables within that scope (better handling of local variables within macros). * Context stack cleanup * % in expressions is interpreted as binary value if immediately followed by 0 or 1 * Add a const directive for labels that shouldn't be allowed to change (currently ignoring const) * TEXT directive converts ascii to petscii (respect uppercase or lowercase petscii) (simplistic) Revisions: * 7 - 65816 support * 6 - 65C02 support * 5 - Merlin syntax * 4 - Object files, relative sections and linking * 3 - 6502 full support * 2 - Moved file out of struse samples * 1 - Built a sample of a simple assembler within struse