updated comments for all vcs examples

LICENSE.txt

@@ -6,6 +6,12 @@ GPLv2
 
 ---
 
+https://github.com/gasman/jsspeccy2
+
+GPLv3
+
+---
+
 https://github.com/sehugg/javatari.js
 
 GNU Affero General Public License v3.0

doc/notes.txt

@@ -69,6 +69,7 @@ TODO:
 - C/asm formatter
 - fix WebAudio (https://news.ycombinator.com/item?id=18066474)
 - Safari: verilog scope doesn't work
+- no errors for verilog inline asm
 
 
 WEB WORKER FORMAT

presets/vcs/examples/adventure.a

@@ -5,6 +5,8 @@
 
 	org  $f000
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
 ; Now, we'll finally put everything together and
 ; make a little person with a hat that can move
 ; back and forth and throw rocks. We'll use one player
@@ -21,6 +23,8 @@
 ;
 ; Note: the Y coordinate goes bottom-top, not top-bottom
 ; as in the next section.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 counter	equ $81 ; increments each frame
 yplyr	equ $82	; player y pos

presets/vcs/examples/bankswitching.a

@@ -1,9 +1,23 @@
-
+
 	processor 6502
         include "vcs.h"
         include "macro.h"
         include "xmacro.h"
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
+; The VCS only supports 4096 bytes of address space for
+; cartridge ROMs, but you can use 8192 or more bytes by
+; using a bank-switching scheme. This lets you map segments
+; of address space to multiple ROM segments.
+;
+; This example demonstrates standard Atari bank-switching, 
+; which just lets you switch multiple segments into the main
+; $1000 bytes of cartridge ROM. Because all bytes must be
+; switched at once, this forces you to build a trampoline --
+; a segment of code that remains valid during the bank-switch
+; process.
+;
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
         seg.u Variables

presets/vcs/examples/bigsprite.a

@@ -4,6 +4,18 @@
         include "macro.h"
         include "xmacro.h"
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
+; This example demonstrates 48-pixel sprites.
+; We'll use a technique similar to the Asynchronous Playfields
+; trick -- reprogramming the TIA registers on-the-fly, writing
+; to each register multiple times during the scanline. If we
+; time our writes carefully, we'll be able to draw six unique
+; sprites per scanline, for example to draw a six-digit
+; scoreboard, or one large 48-pixel sprite.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
 	seg.u Variables
         org $80
 
@@ -12,8 +24,6 @@ LoopCount	byte
 
 THREE_COPIES    equ %011
 
-;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-
 	seg Code
 	org $f000
 

presets/vcs/examples/bitmap.a

@@ -4,11 +4,17 @@
         include "macro.h"
         include "xmacro.h"
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
+; This example demonstrates an asymmetric playfield, which
+; allows different patterns for the left and right sides of
+; the playfield, giving you 40 unique playfied pixels per line.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
         seg.u Variables
 	org $80
 
-;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-
 	seg Code
         org $f000
 

presets/vcs/examples/brickgame.a

@@ -1,22 +1,24 @@
-j
+
 	processor 6502
         include "vcs.h"
         include "macro.h"
         include "xmacro.h"
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
 ; We've got collisions working, but now we'd like some more
 ; interaction. We can make a little "breakout" style game
 ; where the ball knocks out rows of bricks. We'll need to
 ; draw several rows of bricks, any or all of which might be
 ; missing.
-
+;
 ; We'll use a technique called "asychronous playfields".
 ; Remember that the playfield is either symmetric (20 pixels
 ; followed by the same 20 pixels reversed) or repeated (20 pixels
 ; repeated twice). But if we change the playfield registers
 ; *during* the scanline, we can make the second half a
 ; different bitmap than the first half.
-
+;
 ; We're going to move away from the HMPx/HMOVE method of
 ; setting object position and use the SetHorizPos method, since
 ; we really need to know the X position of both player and ball
@@ -24,13 +26,15 @@ j
 ; two scanlines per object. But we do it during the overscan
 ; period at the end of the frame, and we've got the cycles
 ; to spare.
-
+;
 ; Also, we're going to keep score and have a rudimentary
 ; scoreboard, which makes this sort of an actual game!
-
+;
 ; Fun fact: Messing with the HMOVE register causes a "comb"
 ; effect on the left 8 pixels of the screen, which can be seen
 ; at the bottom of the screen in the overscan region.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
         seg.u Variables
         org $80

presets/vcs/examples/collisions.a

@@ -7,6 +7,8 @@
 	seg.u Variables
 	org  $80
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
 ; In this example, we're going to tackle collision detection,
 ; which is one thing in the VCS that's easier than expected.
 ; The TIA has 15 different collision flags that can detect a
@@ -14,19 +16,21 @@
 ; and playfield. You can check these flags at any time (at the
 ; end of the frame is pretty common). When you're done checking
 ; you clear them all at once by writing to CXCLR.
-
+;
 ; For this example we'll use the ball object, and detect collisions
 ; between it and the playfield and the player. We only know
 ; the Y position of the ball and player (the X position is in
 ; the TIA chip) so we'll base our bounce decisions on the Y position
 ; of the ball (for playfield bounces) or the relative Y position of
 ; ball and player (for player bounces).
-
+;
 ; Note: You can press the button to capture the ball.
-
+;
 ; We're going to also include sound, which is generated by writing
 ; a volume register, a frequency register, and a mode register for
 ; one of two channels.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 counter		byte	; increments each frame
 yplyr		byte	; player y pos

presets/vcs/examples/complexscene.a

@@ -4,6 +4,13 @@
         include "macro.h"
         include "xmacro.h"
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
+; This example demonstrates a scene with a full-screen
+; playfield, and a single sprite overlapping it.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
         seg.u Variables
 	org $80
 

presets/vcs/examples/complexscene2.a

@@ -4,6 +4,14 @@
         include "macro.h"
         include "xmacro.h"
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
+; This example demonstrates a scene with a full-screen
+; playfield, and two sprites overlapping it. This takes more
+; CPU time, so our kernel operates in 4-line chunks.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
         seg.u Variables
 	org $80
 

presets/vcs/examples/lines.a

@@ -4,6 +4,13 @@
         include "macro.h"
         include "xmacro.h"
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
+; This example draws a moving line using 16-bit fixed-point
+; math and a missile object.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
         seg.u Variables
 	org $80
 

presets/vcs/examples/missiles.a

@@ -3,8 +3,8 @@
 	include "vcs.h"
 	include "macro.h"
 
-	org  $f000
-
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
 ; Besides the two 8x1 sprites ("players") the TIA has
 ; two "missiles" and one "ball", which are just variable-length
 ; dots or dashes. They have similar positioning and display
@@ -12,6 +12,10 @@
 ; set the horizontal position of any of them.
 ; But we can also use the HMPx/HMOVE registers directly to move the
 ; objects by small offsets without using this routine every time.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+	org  $f000
 
 counter	equ $81
 

presets/vcs/examples/multisprite2.a

@@ -4,13 +4,15 @@
 	include "macro.h"
 	include "xmacro.h"
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
 ; For lots of games, we'd like to display more than two sprites.
 ; There are lots of different ways to tackle this on the VCS,
 ; but we're going to try for a generalized approach that lets
 ; use have N different sprites at any X-Y coordinate, each with
 ; its own bitmap and color table. This is tricky because we can
 ; only do so much on each scanline.
-
+;
 ; Our approach is to separate the problem into three phases.
 ; In the sort phase, we sort all sprites by Y coordinate.
 ; We do one sort pass per frame, so it may take several frames
@@ -20,7 +22,7 @@
 ; coming up. We then allocate it to one of the two player
 ; objects in hardware and set its position using the SetHorizPos
 ; method. We can set one or both of the player objects this way.
-
+;
 ; In the display phase, we display the objects which we previously
 ; assigned and positioned. First we figure out how many scanlines are
 ; required. If only one object is scheduled, we just use its height.
@@ -30,7 +32,7 @@
 ; registers at the appropriate time. We don't have time to do much
 ; else, so we don't look for any new objects to schedule until
 ; we're done with this loop.
-
+;
 ; This scheme can only display up to two objects on a given
 ; scanline, so if the system tries to schedule a third, it will 
 ; be ignored. Also, the positioning routine takes a few scanlines
@@ -52,6 +54,8 @@
 ; There are still some timing issues to fix as you'll see when you
 ; move the adventure person around with the joystick. These might
 ; add additional lines to the display.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 	seg.u Variables
         org $80

presets/vcs/examples/multisprite3.a

@@ -4,13 +4,15 @@
 	include "macro.h"
 	include "xmacro.h"
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
 ; For lots of games, we'd like to display more than two sprites.
 ; There are lots of different ways to tackle this on the VCS,
 ; but we're going to try for a generalized approach that lets
 ; use have N different sprites at any X-Y coordinate, each with
 ; its own bitmap and color table. This is tricky because we can
 ; only do so much on each scanline.
-
+;
 ; Our approach is to separate the problem into three phases.
 ; In the sort phase, we sort all sprites by Y coordinate.
 ; We do one sort pass per frame, so it may take several frames
@@ -20,7 +22,7 @@
 ; coming up. We then allocate it to one of the two player
 ; objects in hardware and set its position using the SetHorizPos
 ; method. We can set one or both of the player objects this way.
-
+;
 ; In the display phase, we display the objects which we previously
 ; assigned and positioned. First we figure out how many scanlines are
 ; required. If only one object is scheduled, we just use its height.
@@ -30,7 +32,7 @@
 ; registers at the appropriate time. We don't have time to do much
 ; else, so we don't look for any new objects to schedule until
 ; we're done with this loop.
-
+;
 ; This scheme can only display up to two objects on a given
 ; scanline, so if the system tries to schedule a third, it will 
 ; be ignored. Also, the positioning routine takes a few scanlines
@@ -41,6 +43,8 @@
 ; sprite entry is missed. In the sort phase, we move those sprites
 ; ahead of lower priority sprites in the sort order. This makes
 ; overlapping sprites flicker instead of randomly disappear.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 	seg.u Variables
         org $80

presets/vcs/examples/musicplayer.a

@@ -6,26 +6,30 @@
 
 	org  $f000
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
 ; This program demonstrates a VCS music player based on tracks
 ; and patterns. A pattern is a list of variable-length notes,
 ; each of which is defined by a pitch and duration.
 ; There are two tracks, one for each audio channel.
 ; Each track consists of a list of patterns, each entry being
 ; a byte offset into the Patterns array.
-
+;
 ; The patterns in the tracks are played in-order until one ends,
 ; and then both tracks are restarted. It's up to the composer
 ; to make sure the durations in each track line up properly.
-
+;
 ; Patterns consist of NOTE or TONE commands. TONE sets the
 ; tone of the channel (the AUDCx register) and NOTE plays a note
 ; with a duration taken from a lookup table.
 ; TONE 0 ends a pattern.
-
+;
 ; Both channels share the same logical array for tracks and patterns,
 ; so both tracks can take up to 255 bytes total, and all patterns
 ; can use up to 255 bytes total.
 ; The music player uses 8 bytes of RAM (not counting stack).
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 Trk0idx		equ	$e0	; offset into tracks for channel 0
 Trk1idx		equ	$e1	; offset into tracks for channel 1

presets/vcs/examples/pal.a

@@ -6,6 +6,8 @@
 
 	org  $f000
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
 ; To output a PAL signal, you need the following:
 ;
 ; - 3 scanlines of VSYNC
@@ -14,23 +16,25 @@
 ; - 36 blank lines
 ;
 ; Total = 312 lines (vs 262 for NTSC)
-
+;
 ; PAL runs at 50 Hz (vs 60 Hz for NTSC)
 ; so your game will run more slowly.
 ; Since you have extra cycles to play with, you could just
 ; call your position update routine twice every five frames.
-
+;
 ; Note also that PAL has different colors than NTSC.
 ; (See http://www.randomterrain.com/atari-2600-memories-tia-color-charts.html)
-
+;
 ; The TIMER_SETUP macro only goes up to 215 lines,
 ; so for the PAL visible frame you would need to use
 ; multiple sections (say 215 + 13 = 228) or count manually
 ; like we do in this example.
-
+;
 ; Many VCS games use conditional defines
 ; (IFCONST and IFNCONST in DASM)
 ; to switch between NTSC and PAL constants.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 ; background color
 BGColor	equ $81

presets/vcs/examples/playfield.a

@@ -4,11 +4,15 @@
 	include "macro.h"
 
 	org  $f000
-	
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;	
 ; We're going to mess with the playfield registers, PF0, PF1 and PF2.
 ; Between them, they represent 20 bits of bitmap information
 ; which are replicated over 40 wide pixels for each scanline.
 ; By changing the registers before each scanline, we can draw bitmaps.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 Counter	equ $81
 

presets/vcs/examples/procgen1.a

@@ -4,6 +4,14 @@
         include "macro.h"
         include "xmacro.h"
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
+; This example uses a linear-feedback shift register to
+; procedurally generate random rooms for the player to walk
+; through.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
 	seg.u   Variables
 	org	$80
 

presets/vcs/examples/retrigger.a

@@ -4,6 +4,18 @@
         include "macro.h"
         include "xmacro.h"
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
+; The sprite retrigger trick relies on a behavior when the
+; NUSIZ register is set to display multiple copies of objects
+; (usually two). Basically, if the RESPx register is strobed
+; multiple times on a given scanline, the first (leftmost) copy
+; of the object will be hidden, and the TIA will draw the other
+; copy. You can keep strobing the register to output multiple
+; copies on the same scanline.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
 	org  $f000
 
 CurRow		equ $8f

presets/vcs/examples/road.a

@@ -3,6 +3,30 @@
         include "macro.h"
         include "xmacro.h"
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
+; This example draws a pseudo-3D road using the two missiles
+; and ball objects. With these, we'll draw the two shoulders
+; of the road, and also the dashed center line.
+;
+; Our plan is this: The two missiles and ball all start at the
+; same position on the horizon. As we go down the screen, we'll
+; move the three objects slightly based on the curve of the road.
+; The left shoulder of the road will be biased a little more to
+; the left, and the right shoulder will bias a little more right.
+; We can use the HMOVE registers for movement, since each object
+; will not need to move more than seven pixels on any given 
+; scanline.
+; 
+; It'd be easier if the scanlines went from bottom to top,
+; because we could just start at the horizontal center of the
+; screen and follow the road curve to the horizon, ending up
+; wherever the road takes us. But scanlines go top to bottom,
+; so we have to also do some preprocessing before the frame begins
+; to figure out where the road ends up.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
         seg.u Variables
 	org $80
 

presets/vcs/examples/score6.a

@@ -4,6 +4,13 @@
         include "macro.h"
         include "xmacro.h"
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
+; This example uses the 48-pixel retriggering method to display
+; a six-digit scoreboard.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
         seg.u Variables
 	org $80
 

presets/vcs/examples/scoreboard.a

@@ -4,6 +4,15 @@
         include "macro.h"
         include "xmacro.h"
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
+; This example draws a scoreboard using the playfield
+; and a 4x5 font. We encode the left and right digits in a
+; single byte, so we just mask one side or the other, and
+; combine them into a 8-bit byte to draw a digit.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
 	seg.u Variables
         org $80
 

presets/vcs/examples/sprite.a

@@ -5,6 +5,8 @@
 
 	org  $f000
 	
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
 ; Sprites are a tricky beast on the 2600.
 ; You only have two of them.
 ; They are 8 bits wide and 1 bit high.
@@ -14,6 +16,8 @@
 ; To position Y, you simply wait until the desired scanline and
 ; set the bits of your sprite to a non-zero value.
 ; Having fun yet? :)
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 Counter	equ $81
 

presets/vcs/examples/tigervision[3E].a

@@ -1,4 +1,4 @@
-
+
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; 64K Tigervision bank-switching example

presets/vcs/examples/timing1.a

@@ -5,12 +5,16 @@
 
 	org  $f000
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
 ; We're going to try to animate sprites horizontally.
 ; Remember, we have to pause the CPU until the exact moment the
 ; scanline hits the desired horizontal position of the sprite.
 ; Since we can't hard-code the SLEEP macro we'll have to do it
 ; dynamically somehow. But since the TIA beam is racing so much
 ; faster than the CPU clock, we'll have to be clever.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 counter	equ $81
 

presets/vcs/examples/timing2.a

@@ -5,6 +5,8 @@
 
 	org  $f000
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
 ; We're going to use a more clever way to position sprites
 ; ("players") which relies on additional TIA features.
 ; Because the CPU timing is 3 times as coarse as the TIA's,
@@ -12,6 +14,8 @@
 ; CPU delays alone.
 ; Additional TIA registers let us nudge the final position
 ; by discrete TIA clocks and thus target all 160 positions.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 counter	equ $81
 

presets/vcs/examples/tinyfonts2.a

@@ -4,10 +4,30 @@
         include "macro.h"
         include "xmacro.h"
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
+; Now that we know how to draw extra-wide sprites, we can
+; apply this technique to another type of object: text.
+;
+; We can draw scoreboards and other kinds of text using the
+; playfield registers. However, these are pretty blocky, and
+; limited to 40 pixels in width. But we can draw lines of text
+; that are 48 pixels width by five pixels high using the
+; sprite retriggering trick.
+;
+; Instead of fetching our bitmap data from ROM, we build a 
+; bitmap in RAM using lookup tables. Building the bitmap array
+; efficiently is a challenge, because we've got to look up 60
+; bytes in memory and combine those into 30 bytes. If we did
+; this without regard to performance, it might consume a few
+; thousand CPU cycles, which would require 30 or 40 scanlines
+; just to set up the sprite.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
         seg.u Variables
 	org $80
 
-
 Temp		.byte
 WriteOfs	.byte ; offset into dest. array FontBuf	
 LoopCount	.byte ; counts scanline when drawing

presets/vcs/examples/wavetable.a

@@ -4,6 +4,14 @@
         include "macro.h"
         include "xmacro.h"
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;
+; This example drives the VCS audio DAC directly to generate
+; 4-voice music. Unfortunately, the CPU is 100% utilized so
+; we can't display anything.
+;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
 	seg.u   Variables
 	org	$80