MESS OUT

=MESS_OUT ($C004CE): Generic VRAM output=

MESS_OUT executes the command buffer in the BIOS's work RAM that starts at BIOS_MESS_BUFFER (constant $10FF00) and goes up to BIOS_MESS_POINT (longword variable $10FDBE). This can be used to display text messages, boxes... on the fix layer (is it used for sprites too ?).

MESS_OUT is automatically called in the SYSTEM_INT1 call. BIOS_MESS_BUSY ($10FDC2.b) can be used to prevent this (when setting up the command list, for example).

The command buffer can be made of commands directly, or pointers to lists in ROM or user RAM. To put commands directly into the buffer, a null pointer ($00.l) needs to be placed before the command list.

Commands are always words.

Command 0
End of actual command list.
 * 1 word

Command 1

 * 2 words

This command specifies if the data will be in bytes or words, and if the size is defined or if an end code has to be reached.


 * If data is in bytes (bit 10 = 0):
 * The next word's upper byte will be the data's constant upper byte (since VRAM can only be written in words).
 * If the data is limited by an end code (bit 9 = 0), the next word's lower byte will be the end code's value.
 * If the data size is defined (bit 9 = 1), the next word's lower byte will be the size (so max length is $FF).


 * If data is in words (bit 10 = 1):
 * If the data is limited by an end code (bit 9 = 0), the next word will be the end code's value.
 * If the data size is defined (bit 9 = 1), the next word will be the size (so max length is $FFFF).

Examples: dc.w $0001,$15FF  ;Data will be read in bytes, upper byte will always be $15, end code is $FF. dc.w $0101,$1520  ;Data will be read in bytes, upper byte will always be $15, data length is $20. dc.w $0201,$8000  ;Data will be read in words, end code is $8000. dc.w $0301,$2044  ;Data will be read in words, data length is $2044.

The format stays the same until command 1 is used again.

Command 2

 * 1 word

Sets the auto-increment value (written to VRAM_MOD ($3C0004)). Is the value sign-extended or not ? dc.w $2002  ;Set auto-inc to $20

Command 3
Sets the VRAM address written to VRAM_ADDR ($3C0000)) to the next word's value. dc.w $0003,$7201  ;Set VRAM address to $7201
 * 2 words

Command 4
Sets the output data address to the next longword. Actual writes to VRAM are done with this command. dc.w $0004 dc.l MESSAGE
 * 3 words

Command 5
Add the next word to the current VRAM address. (This is different from command 2). Useful to skip lines or spaces. dc.w $0005,$001F  ;Add $1F to the current VRAM address
 * 2 words

Command 6
Resume data output (instead of using command 4 again, keep going from the last address).
 * 1 word

Command 7
Directly define the data (instead of using command 4 to point to it). Don't forget the padding byte if the data ends on an odd address. dc.w $0007 dc.b $30,$31,$34,$45,$FF dc.b $00    ;Pad byte
 * at least 2 words

Command 8

 * at least 2 words

Writes with the 8*16 pixels fix font. The commands upper byte will be the data's constant upper byte. The next bytes are data, and the end code is $FF.

The auto-inc is automaticaly set to $20.

dc.w $0108    ;Tileset 1 dc.b $44,$51  ;Data dc.b $FF      ;End code dc.b $00      ;Pad byte

Command 9
Same as command 9 but for japanese characters.

Command A
Call sub command list. The next longword is a pointer to another command list. Return has to be made using command B. dc.w $000A dc.l SUBLIST
 * 3 words

Command B
Return to calling command list.
 * 1 word

Command C
Repeat output. The upper byte of the command is the number of times to output the next word.
 * 2 words

dc.w $090C,$0147  ;Outputs $0147 9 times

Command D

 * 2 words

Repeat and increment output. The upper byte of the command is the number of times to output the next word. The lower byte of the data is incremented each time. dc.w $040D,$42FE  ;Outputs $42FE,$42FF,$4200,$4201

=Example code and command lists= (Slightly modified code from SNK's doc, output gives the above screencap.)

bset.b #0,BIOS_MESS_BUSY movea.l BIOS_MESS_POINT,a0 ;Get current pointer in buffer move.l #0,(a0)+       ;Direct commands move.w #3,(a0)+       ;Set VRAM address to $7318 move.w #$7318,(a0)+ move.w #$0301,(a0)+   ;Words, size = 1 move.w #$0001,(a0)+ move.w #$0007,(a0)+   ;Output data move.w $100000,(a0)+ move.w #0,(a0)+       ;End of this list move.l #MESSAGE1,(a0)+ ;Pointer to list in ROM move.l a0,BIOS_MESS_POINT  ;Update pointer bclr.b #0,BIOS_MESS_BUSY   ;Ready to go rts

MESSAGE1: dc.w $0001    ;Bytes, upper = $00, end code = $FF dc.w $00FF dc.w $2002    ;Auto-inc = $20 dc.w $0003    ;VRAM address = $7024 dc.w $7024 dc.w $0004    ;Write "MESSAGE1" dc.l MS1

dc.w $0005    ;Next line dc.w $0001 dc.w $0006    ;Resume, write "MESSAGE2" dc.w $0005    ;Next line dc.w $0001

dc.w $0007    ;Direct data output dc.b "MESSAGE3" dc.w $FF00    ;End code and pad byte

dc.w $0005    ;Next line dc.w $0001

dc.w $0108    ;8x16 write, fontset 1 dc.b "ABCDE",$FF dc.w $0005    ;Next line dc.w $0001 dc.w $0109    ;8x16 write, fontset 1 dc.b 0,1,2,3,4,$FF dc.w $0005    ;Next 2 lines dc.w $0002 dc.w $000A    ;Sub list calls dc.l SUB_MESS dc.w $000A dc.l SUB_MESS dc.w $000A dc.l SUB_MESS dc.w $0000

MS1: dc.b "MESSAGE 1",$FF dc.b "MESSAGE 2",$FF

SUB_MESS: dc.w $090C    ;Outputs $0022 9 times dc.w $0022 dc.w $070D    ;Outputs $0042 7 times with inc dc.w $0042 dc.w $0005    ;Next line dc.w $0001 dc.w $000B    ;Return