19. Things you should know about coding for…

Please be aware that the source code files in there are mainly used to test that the compiler and linker work, they are not possibly good examples of how you should write code using WLA DX.

19.1. Z80

Check the Z80 specific directives. All SMS/GG coders should find .SMSTAG, .SDSCTAG and .COMPUTESMSCHECKSUM very useful…

There are shadow register aliases for opcodes that use registers A, F, BC, DE and HL. The shadow register versions are just for convenience, if the programmer wants to explicitly show that he is now using the shadow registers. For example:

AND A ; (original, assembles to 0xA7) AND A’ ; (alias, assembles to 0xA7 and is in reality “AND A”)

Opcodes that make relative label references:

JR *
DJNZ

19.2. 6502

For example mnemonics ADC, AND, ASL, etc… cause problems to WLA, because they take different sized arguments. Take a look at this:

LSR 11       ; $46 $0B
LSR $A000    ; $4E $00 $A0

The first one could also be

LSR 11       ; $4E $0B $00

To really get what you want, use .8BIT, .16BIT and .24BIT directives. Or even better, supply WLA the size of the argument:

LSR 11.W     ; $4E $0B $00

Opcodes that make relative label references:

BCC
BCS
BEQ
BMI
BNE
BPL
BVC
BVS

19.3. 65C02

Read the subsection 6502 as the information applies also to 65C02 coding…

Opcodes that make relative label references:

BCC
BCS
BEQ
BMI
BNE
BPL
BVC
BVS
BRA
BBR*
BBS*

19.4. 65CE02

Read the subsection 6502 as the information applies also to 65CE02 coding…

Opcodes that make relative label references:

BCC
BCS
BEQ
BMI
BNE
BPL
BVC
BVS
BRA
BSR
BBR*
BBS*

19.5. 65816

Read the subsection 6502 as the information applies also to 65816 coding…

WLA-65816 has also few SNES specific directives which are all very helpful. Remember that when you use .LOROM, .HIROM, .SLOWROM and .FASTROM WLA automatically writes the information into the output. .COMPUTESNESCHECKSUM, .SNESHEADER and few others could also be useful.

Use .BASE to set the upmost eight bits of 24-bit addresses.

If possible, use operand hints to specify the size of the operand. WLA is able to deduce the accumulator/index mode to some extent from REP/SEP-mnemonics and .ACCU and .INDEX-directives, but just to be sure, terminate the operand with .B, .W or .L.

AND #10    ; can be two different things, depending on the size of the operand.
AND #10.B  ; forces 8-bit immediate value.
AND #10.W  ; forces 16-bit immediate value.

AND 10     ; can be three different things, depending on the size of the operand.
AND 10.B   ; forces 8-bit address.
AND 10.W   ; forces 16-bit address.
AND 10.L   ; forces 24-bit address.

Or if you must, these work as well:

AND.B #10  ; the same as "AND #10.B".
AND.W #10  ; the same as "AND #10.W".

AND.B 10   ; the same as "AND 10.B".
AND.W 10   ; the same as "AND 10.W".
AND.L 10   ; the same as "AND 10.L".

Opcodes that make relative label references:

BCC
BCS
BEQ
BMI
BNE
BPL
BVC
BVS
BRA
BRL
PER

Use .WDC to start parsing WDC standard assembly code. .NOWDC sets the parser to parse WLA syntax assembly code.

MVN and MVP work as follows:

MVN $xx, $yy
MVN $xxyy
MVP $xx, $yy
MVP $xxyy

xx is the source bank, yy is the target bank.

19.6. MC68000

In addition to operand hints .B, .W and .L we also have .D (32-bit).

19.7. HUC6280

Read the subsection 6502 as the information applies also to HUC6280 coding…

As PC Engine’s zero page starts at $2000 (imagine ZEROPAGE1 label’s address is $2001), operand hint .#b will be useful:

STA ZEROPAGE1.#B  ; $85 $01

It takes the lowest 8 bits of ZEROPAGE1 and hints the assembler’s parser that the operand is 8 bits in size.

Opcodes that make relative label references:

BCC
BCS
BEQ
BMI
BNE
BPL
BVC
BVS
BSR
BBR*
BBS*

19.8. SPC-700

Note that you’ll have to put an exclamation mark before a 16-bit value. For example,

CALL !Main
AND  A, !$1000

Opcodes that make relative label references:

BCC
BCS
BEQ
BMI
BNE
BPL
BVC
BVS
BRA
BBS
BBC
CBNE *
DBNZ *

19.9. Pocket Voice (GB-Z80)

Pocket Voice uses its own MBC. You can enable Pocket Voice mode by selecting Pocket Voice cartridge type ($BE in $0147) and defining correct .ROMBANKMAP and .MEMORYMAP. In PV mode bank 0 is 24KB and the rest are 8KB.

Note that WLA assumes that ROM offset is all the time 0. If you use something else as the offset, make sure to compute the jumps by hand as WLA cannot do that.

Check out tests/gb-z80/include/pocket_voice.i for more information.

19.10. GB-Z80

WLA outputs only $10 when it decodes STOP. Often it’s necessary to put an extra NOP ($00) after a STOP, and sometimes something else, but that’s left entirely to the user.

Opcodes that make relative label references:

JR *