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Carl-Henrik Skårstedt 662982404b Link issues 
- Map symbols might not have been updated with their labels
- Relocation index may be off
- Map symbols stored in 16 bits causing truncation of value in symbol
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- Added a tool to dump the values in object files
2015-10-27 20:57:14 -07:00

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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
  • Basic relative sections and linking.
  • C style scoping within '{' and '}': 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 can be defined in a number of ways, such as leading period (.label) or leading at-sign (@label) or terminating dollar sign (label$).
  • 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, -endm adds support for sources using macro/endmacro and repeat/endrepeat combos rather than scoeps).

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

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=6502/6502ill/65c02/65c02wdc/65816: assemble with opcodes for a different cpu
  • -acc=8/16: start assembling with accumulator immediate mode instruction size 8 or 16 bits
  • -xy=8/16: start assembling with index register immediate mode instruction size 8 or 16 bits
  • -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 for current CPU (file or stdout)
  • -sect: display sections loaded and built
  • -vice (file.vs): export a vice symbol file
  • -endm: macro and rept end with endm/endr or endmacro/endrepeat 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 directive. To control the final layout of code and data a 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 Set the CPU to assemble for.
  • ORG (same as PC): Set the current compiling address.
  • LOAD Set the load address for binary formats that support it.
  • SECTION Start a relative section
  • LINK Link a relative section at this address
  • XDEF Make a label available globally
  • INCOBJ Include an object file (.x65) to this file
  • EXPORT Save out additional binary files with argument appended to filename
  • ALIGN Align the address to a multiple by filling with 0s
  • MACRO Declare a macro
  • EVAL Log an expression during assembly.
  • BYTES Insert comma separated bytes at this address (same as BYTE or DC.B)
  • WORDS Insert comma separated 16 bit values at this address (same as WORD or DC.W)
  • TEXT Insert text at this address
  • INCLUDE Include another source file and assemble at this address
  • INCBIN Include a binary file at this address
  • IMPORT Catch-all file inclusion (source, bin, text, object, symbols)
  • CONST Assign a value to a label and make it constant (error if reassigned with other value)
  • LABEL Decorative directive to assign an expression to a label
  • INCSYM Include a symbol file with an optional set of wanted symbols.
  • POOL Add a label pool for temporary address labels
  • #IF / #ELSE / #IFDEF / #ELIF / #ENDIF Conditional assembly
  • STRUCT Hierarchical data structures (dot separated sub structures)
  • REPT Repeat a scoped block of code a number of times.
  • INCDIR Add a directory to look for binary and text include files in.
  • 65816 A16/A8/I16/I8 Directives to control the immediate mode size
  • 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 $fe
	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' 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 (<line#>) <message>: <expression> = <evaluated expression>" 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"

IMPORT

Insert multiple types of data or code at the current address. Import takes an additional parameter to determine what to do with the file data, and can accept reading in a portion of binary data.

The options for import are:

  • source: same as INCLUDE
  • binary: same as INCBIN
  • c64: same as INCBIN but skip first two bytes of file as if this was a c64 prg file
  • text: include text data from another file, default is petscii otherwise add another directive from the TEXT directive
  • object: same as INCOBJ
  • symbols: same as INCSYM, specify list of desired symbols prior to filename.

After the filename for binary and c64 files follow comma separated values for skip data size and max load size. c64 mode will add the two extra bytes to the skip size.

	import source "EQ.S"
	import binary "GFX.BIN",0,256
	import c64 "FONT.BIN",8,8*26
	import text petscii_shifted "LICENSE.TXT"
	import object "engine.x65"
	import symbols InitEffect, UpdateEffect "effect.sym"

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 '

Example:

Function_Name: {
	pool zpWork $f6-$100		; these zero page addresses are available for temporary labels
	zpWork zpTrg.w				; zpTrg will be $fe
	zpWork zpSrc.w				; zpSrc will be $fc

	lda #>Src
	sta zpSrc
	lda #<Src
	sta zpSrc+1
	lda #>Dest
	sta zpDst
	lda #<Dest
	sta zpDst+1

	{
		zpWork zpLen			; zpLen will be $fb
		lda #Length
		sta zpLen
	}
	nop
	{
		zpWork zpOff			; zpOff will be $fb (shared with previous scope zpLen)
	}
	rts

#IF / #ELSE / #IFDEF / #ELIF / #ENDIF

Conditional code parsing is very similar to C directive conditional compilation.

Example:

DEBUG = 1

#if DEBUG
    lda #2
#else
    lda #0
#endif

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 <count> { <code> }. The full word REPEAT is also recognized.

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
}

Note that if the -endm command line option is used (macros are not defined with curly brackets but inbetween macro and endm*) this also affects rept so the syntax for a repeat block changes to

.REPEAT 4
	lsr
.ENDREPEAT

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.

Note that in case a 4 digit hex value is used in 8 bit mode and an immediate mode is allowed but is not currently enable a two byte value will be emitted

	lda #$0043	; will be 16 bit regardless of accumulator mode if in 65816 mode
	lda #$43	; will be 8 bit or 16 bit depending on accumulator mode

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.

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 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.

DSK

DSK is similar to SAV

ENT

ENT defines the label that preceeds it as external

EXT

EXT imports an external label, x65 doesn't need this.

LNK / STR

LNK links the contents of an object file, to fit with the named section method of linking in x65 this keyword has been reworked to have a similar result, the actual linking doesn't begin until the current section is complete.

ADR

Define byte triplets (like DA but three bytes instead of 2)

ADRL

Define values of four bytes.

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

Conditional operators

  • ==: Double equal signs yields 1 if left value is the same as the right value
  • <: If inbetween two values, less than will yield 1 if left value is less than right value

  • : If inbetween two values, greater than will yield 1 if left value is greater than right value

  • <=: If inbetween two values, less than or equal will yield 1 if left value is less than or equal to right value

  • =: If inbetween two values, greater than or equal will yield 1 if left value is greater than or equal to right value

Example:

lda #(((>SCREEN_MATRIX)&$3c)*4)+8
sta $d018

Avoid using parenthesis as the first character of the parameter of an opcode that can be relative addressed instead of an absolute address. This can be avoided by

	jmp (a+b)	; generates a relative jump
	jmp.a (a+b)	; generates an absolute jump
	jmp +(a+b)	; generates an absolute jump

c = (a+b)
	jmp c		; generates an absolute jump
	jmp a+b		; generates an absolute jump

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 a limited release and while all features are in place and tested, more testing is needed to verify the completeness. Primarily tested with personal archive of sources written for Kick assmebler, DASM, TASM, XASM, etc. and passing most of Apple II Prince of Persia and Pinball Construction set.

TODO

  • irp (indefinite repeat)

FIXED

Revisions:

  • 8 - Linking tested and passed with external project (Apple II gs Rastan)
  • 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