Lab 7: Read the controller

Wow!  Real player control!  In this lab, we cover how to strobe and read
the dpad buttons and hook it in to the existing "engine", such as it is,
so that the little character runs forward only when controlled to do so.

The process is easy, involving strobing the button state into a shift
register and reading it back.  There are some pretty standard algorithms
for doing this, but again, the goal of many of these labs is to make
something as plain and readable as possible first.

diff --git a/README.md b/README.md
index 04fa0e020a012b52ec65bc25745fc166e50d7f41..de8dfe5587363003254562a65d34c30a4b6ab1cf 100644 (file)
--- a/README.md
+++ b/README.md
@@ -26,6 +26,8 @@ demos/labs, please look at the labXX branches.  Current ones include:
 * Lab 3: Pattern, name, and attribute tables
 * Lab 4: Drawing sprites
 * Lab 5: Animating sprites
+* Lab 6: APU init and playing sound
+* Lab 7: Reading the controllers
 
 To build and run:
 ```

diff --git a/src/sprite.asm b/src/sprite.asm
index de5627bfbac83d044f0d9166bb1f1f5cd65ea7f8..2ca8e30776a3e25dba03a6906e31c8c6aa2269d6 100644 (file)
--- a/src/sprite.asm
+++ b/src/sprite.asm
@@ -1,32 +1,42 @@
-; Audio Processing Unit (APU) Basics
+; NES Controller Basics
 ;
-; This lab introduces some very basic code for initializing the RP2A03 APU
-; (used by the NTSC NES) and generating a single sound.  Again, this is done
-; not with a focus on efficacy or efficiency but instead for readability and
-; documentation focused on explaining the roles of various registers.
+; This lab introduces some incredibly basic code for reading the controller
+; state.  This will work in the most basic scenario, which is for reading a
+; standard NES dpad controller, which most emulators will support out of the
+; box.
 ;
-; First off, there's the initialization of the registers to clear, known
-; states.  This is done in the main routine prior to turning on the NMI.
-; recall from previous materials that the NMI provides a heartbeat for the
-; video processing and display, and as such, it's better to do all
-; initialization prior to turning on the NMI.  Since we're going to be playing
-; only one (pretty ugly) sound, we also go ahead and configure that in the
-; main intitialization code, too.
+; The controller interface works as follows:
+; * Writing to the controller register with the strobe bit active causes the
+;   controller's latches to run in "parallel" mode.  Any reads from the
+;   register at this time will give real-time updates on the state of the first
+;   button of the controller (for a dpad, that's A).
+; * A subsequent write to the register with the strobe bit inactive latches in
+;   the last state of the buttons and a shift register will let you read them
+;   out, one button per read.  Different controllers will report on different
+;   bits in the read, but the standard dpad will always report on bit 0.
 ;
-; Essentially, making a sound through the synthesizers works in a common way
-; across all of them: you write in paramters describing the period (the inverse
-; of the frequency) and the volume.  After that, you write a value into the
-; length counter bits which describes how many ticks of the frame counter
-; (running at 240 Hz on the 4-frame config used here) the sound should last.
+; Want to know more about controller reading?  See here:
 ;
-; Muting a channel can be performed through the DMC_LEN_CNT_CTRL_STA register.
-; The bottom 5 bits enable/disable the length counters for the synthesizers,
-; thus effectively muting them.
+; * http://wiki.nesdev.com/w/index.php/Standard_controller
+; * http://wiki.nesdev.com/w/index.php/Controller_reading
+; * http://wiki.nesdev.com/w/index.php/Controller_reading_code
 ;
-; There's enough in this lab to get your feet wet on the APU, but it doesn't
-; cover more advanced topics like sweeps, envelopes, samples, or composing
-; music.
-
+; Really, that's it.  Just for this lab, the R button now controls the walk
+; animation, so the little man now runs only when you tell him to.  To achieve
+; this, I simply inhibit the walk cycle animation unless the button has been
+; pressed.  I sample constantly in the main loop and set a flag, which the
+; NMI vector checks before performing any animations.
+;
+; Believe it or not, at this point, we know enough to make bigger and better
+; applications.  But this code here is horribly structured for doing so.  So,
+; in my next lab, I'm going to clean this up, reorganize it, and try to make
+; a more workable "engine" on which to put advanced topics.
+;
+; Tiny note: I changed the ZEROPAGE to DATA here merely for correctness' sake.
+; The ZEROPAGE should always contain unitialized data, but some of the data
+; was initialized and this gives a linker warning.
+;
+; Thanks again for reading this far and taking this NES 6502 journey with me!
 
 .define SPRITE_PAGE  $0200
 
@@ -87,6 +97,13 @@
 ; Frame counter mode (4 or 5 frame), frame counter interrupt enable/disable
 .define FRAME_CNT_MODE_INT $4017
 
+; Controller 1
+.define CONTROLLER_1_PORT $4016
+.define CONTROLLER_2_PORT $4017
+.define CONTROLLER_STROBE $01
+.define CONTROLLER_LATCH  $00
+.define CONTROLLER_D0_BIT $01
+
 ; Mandatory iNES header.
 .segment "HEADER"
 
@@ -100,7 +117,7 @@
 
 ; "zero page" RAM
 ; This is where we're storing our mutable state.
-.segment "ZEROPAGE"
+.segment "DATA"
 current_frame:
   .byte 0
 sprite_x:
@@ -109,7 +126,8 @@ sprite_y:
   .byte $7F
 frame_count:
   .byte 0
-
+run:
+  .byte 0
 
 
 ; code ROM segment
@@ -210,6 +228,28 @@ zero_oam:
   sta PPUCTRL
 
 forever:
+; read the controller state
+  lda #CONTROLLER_STROBE
+  sta CONTROLLER_1_PORT
+  lda #CONTROLLER_LATCH
+  sta CONTROLLER_1_PORT
+; The controller state is latched, the bits will report in in this
+; order on subsequent reads: A, B, Select, Start, U, D, L, R
+;
+; We only care about the 0 bit because that's where D0, the standard
+; controller, reports in
+  lda CONTROLLER_1_PORT ; A
+  lda CONTROLLER_1_PORT ; B
+  lda CONTROLLER_1_PORT ; Select
+  lda CONTROLLER_1_PORT ; Start
+  lda CONTROLLER_1_PORT ; U
+  lda CONTROLLER_1_PORT ; D
+  lda CONTROLLER_1_PORT ; L
+  lda CONTROLLER_1_PORT ; R
+  and #CONTROLLER_D0_BIT
+; A value of 0 means the button is pressed
+  sta run
+
   jmp forever
 
 nmi:
@@ -230,6 +270,11 @@ nmi:
   lda #0
   sta frame_count
 
+; If run is 0, don't do anything
+  lda run
+  cmp #0
+  beq done
+
 ; We counted 15 NMIs, so let's update the animation frame and
 ; make the little character walk
   lda current_frame