Add the sound/beep.s example

This is the most simple example you can come up when it comes to
producing sound on the NES/Famicom. Basically, a single note is
delivered to the APU which is continuously on.

Signed-off-by: Miquel Sabaté Solà <mssola@mssola.com>

4 files changed, 36 insertions, 0 deletions

diff --git a/shared/apu.s b/shared/apu.s
new file mode 100644
index 0000000..814c446
--- /dev/null
+++ b/shared/apu.s
@@ -0,0 +1,8 @@
+.scope APU
+    m_square_1_envelope = $4000
+    m_square_1_low      = $4002
+    m_square_1_high     = $4003
+    m_dmc               = $4010
+    m_status            = $4015
+    m_frame_counter     = $4017
+.endscope
diff --git a/shared/asm.s b/shared/asm.s
index 67b195c..e67b7a6 100644
--- a/shared/asm.s
+++ b/shared/asm.s
@@ -20,3 +20,11 @@
 .macro JAL ADDR
     jmp ADDR
 .endmacro
+
+;; The __fallthrough__ special statement allows developers to explicitly tell
+;; the assembler that a "fall through" situation does not happen by mistake.
+.ifndef __NASM__
+  .macro __fallthrough__ arg
+    ;; NOTE: nothing to do :)
+  .endmacro
+.endif
diff --git a/shared/oam.s b/shared/oam.s
new file mode 100644
index 0000000..ff23d64
--- /dev/null
+++ b/shared/oam.s
@@ -0,0 +1,11 @@
+.scope OAM
+    m_addr = $2003
+    m_dma  = $4014
+.endscope
+
+.macro OAM_WRITE_SPRITES
+    lda #$00
+    sta OAM::m_addr
+    lda #$02
+    sta OAM::m_dma
+.endmacro
diff --git a/shared/ppu.s b/shared/ppu.s
index 42acb06..8b548e9 100644
--- a/shared/ppu.s
+++ b/shared/ppu.s
@@ -9,3 +9,12 @@
     lda #value
     sta $2007
 .endmacro
+
+.scope PPU
+    m_control = $2000
+    m_mask    = $2001
+    m_status  = $2002
+    m_scroll  = $2005
+    m_address = $2006
+    m_data    = $2007
+.endscope