Initial commitHEADmain

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

19 files changed, 1675 insertions, 0 deletions

diff --git a/.gitattributes b/.gitattributes
new file mode 100644
index 0000000..1a6c279
--- /dev/null
+++ b/.gitattributes
@@ -0,0 +1 @@
+assets/* linguist-generated
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..1849194
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+out/
+TODO
+*.patch
diff --git a/.nasm/addresses.txt b/.nasm/addresses.txt
new file mode 100644
index 0000000..774e129
--- /dev/null
+++ b/.nasm/addresses.txt
@@ -0,0 +1,10 @@
+nmi,8008,8028
+irq,8028,8029
+reset,8029,809B
+reset::reset_mmc1,803D,803D
+reset::@vblankwait1,8043,8043
+reset::@sprite_reset_loop,804C,804C
+reset::@vblankwait2,805F,805F
+main,809B,80A1
+main::@tbd,809E,809E
+Btree::todo,C000,C001
diff --git a/.nasm/memory.txt b/.nasm/memory.txt
new file mode 100644
index 0000000..0bde330
--- /dev/null
+++ b/.nasm/memory.txt
@@ -0,0 +1,17 @@
+$0180-$01FF: <stack>
+$0200-$02FF: OAM::m_sprites
+$2000: PPU::m_control
+$2001: PPU::m_mask
+$2002: PPU::m_status
+$2003: OAM::m_address
+$2005: PPU::m_scroll
+$4010: APU::m_dmc
+$4014: OAM::m_dma
+$4017: APU::m_frame_counter
+$8000: MMC1::m_control
+$A000: MMC1::m_chr_bank
+$E000: MMC1::m_prg_bank
+
+--- Summary (in bytes) ---
+- Internal RAM: 384/2048 (18.75%)
+- Working RAM: 0/8192 (0.00%)
diff --git a/.nasm/segments.txt b/.nasm/segments.txt
new file mode 100644
index 0000000..8799302
--- /dev/null
+++ b/.nasm/segments.txt
@@ -0,0 +1,5 @@
+- HEADER: 16/16 (100%)
+- PRG0: 161/16384 (0.98%)
+- PRG1: 1/16378 (0.01%)
+- ROMV: 6/6 (100%)
+- ROM2: 8192/8192 (100%)
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..f288702
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,674 @@
+                    GNU GENERAL PUBLIC LICENSE
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+excuse you from the conditions of this License.  If you cannot convey a
+covered work so as to satisfy simultaneously your obligations under this
+License and any other pertinent obligations, then as a consequence you may
+not convey it at all.  For example, if you agree to terms that obligate you
+to collect a royalty for further conveying from those to whom you convey
+the Program, the only way you could satisfy both those terms and this
+License would be to refrain entirely from conveying the Program.
+
+  13. Use with the GNU Affero General Public License.
+
+  Notwithstanding any other provision of this License, you have
+permission to link or combine any covered work with a work licensed
+under version 3 of the GNU Affero General Public License into a single
+combined work, and to convey the resulting work.  The terms of this
+License will continue to apply to the part which is the covered work,
+but the special requirements of the GNU Affero General Public License,
+section 13, concerning interaction through a network will apply to the
+combination as such.
+
+  14. Revised Versions of this License.
+
+  The Free Software Foundation may publish revised and/or new versions of
+the GNU General Public License from time to time.  Such new versions will
+be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
+
+  Each version is given a distinguishing version number.  If the
+Program specifies that a certain numbered version of the GNU General
+Public License "or any later version" applies to it, you have the
+option of following the terms and conditions either of that numbered
+version or of any later version published by the Free Software
+Foundation.  If the Program does not specify a version number of the
+GNU General Public License, you may choose any version ever published
+by the Free Software Foundation.
+
+  If the Program specifies that a proxy can decide which future
+versions of the GNU General Public License can be used, that proxy's
+public statement of acceptance of a version permanently authorizes you
+to choose that version for the Program.
+
+  Later license versions may give you additional or different
+permissions.  However, no additional obligations are imposed on any
+author or copyright holder as a result of your choosing to follow a
+later version.
+
+  15. Disclaimer of Warranty.
+
+  THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
+APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
+HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
+OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
+IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..b04fce7
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,52 @@
+V =
+ifeq ($(strip $(V)),)
+	E = @echo
+	Q = @
+else
+	E = @\#
+	Q =
+endif
+
+# CC65 is set to `xa65` if that exists, otherwise we resort to `cl65` by default.
+XA65_BIN := $(shell command -v xa65 2>/dev/null)
+ifneq ($(XA65_BIN),)
+	CC65   ?= xa65
+else
+	CC65   ?= cl65
+endif
+
+# NOTE: you can configure `CC65` and `CCOPTS` with the compiler and its options
+# that you might require.
+CCOPTS ?= --target nes
+
+# Be strict when using xa65, and extra verbose if V=1.
+ifeq ($(CC65),xa65)
+	CCOPTS += --strict --stats
+endif
+
+##
+# all: clean the workspace and build the ROM file.
+
+.PHONY: all
+all: clean deps build
+
+##
+# clean & deps: clean the workspace and check that all dependencies are met.
+
+.PHONY: clean
+clean:
+	$(Q) rm -rf out
+	$(Q) find . -type f -name "*.nes" -delete
+	$(Q) rm -rf .nasm/
+	$(Q) mkdir -p out/
+
+.PHONY: deps
+deps:
+	@which $(CC65) >/dev/null 2>/dev/null || (echo "ERROR: '$(CC65)' not found." && false)
+
+##
+# build: create the ROM file.
+
+.PHONY: build
+build:
+	$(Q) $(CC65) $(CCOPTS) src/btree.s -C config/mmc1.cfg -o out/btree.nes 1>/dev/null
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..c87a374
--- /dev/null
+++ b/README.md
@@ -0,0 +1,59 @@
+Manipulate B-Trees with your NES/Famicom controller. This is basically an
+implementation of COW-friendly B-Trees in pure 6502 assembly, with a little UI
+on top of it just to showcase it.
+
+## The "game"
+
+The "game" is just a file explorer. Use the arrow keys to go up/down the list,
+and press <kbd>A</kbd> or <kbd>Start</kbd> to edit one of the files. There's
+also the option to create a new file. Press <kbd>A</kbd> or <kbd>Start</kbd> and
+it will prompt you to give it a unique name. With that, a file will be created
+and you will jump into edit mode.
+
+You can edit the file currently selected with the following button mapping:
+
+- <kbd>B</kbd>: change the character.
+- <kbd>A</kbd>: write the character in place.
+- <kbd>Arrows</kbd>: move around the document.
+- <kbd>Start</kbd>: save the file.
+- <kbd>Select</kbd>: go back to the file explorer.
+
+## Internal design
+### The data structure
+
+The main data structure is a COW-friendly B-tree (just like filesystems like
+[btrfs](https://btrfs.readthedocs.io/en/latest/)). You can read all about them
+[here](https://btrfs.readthedocs.io/en/latest/dev/dev-btrfs-design.html). To sum
+things up, these are B+-trees which:
+
+1. Are updated top-down.
+2. Leaf nodes are not chained.
+3. Storage management is done via delayed reference counting.
+
+Here we have the invariant that a node has between 2 to 5 elements before it
+gets split or merged. When a modification happens, it's done top-down, and all
+modified elements are copied in a new location: the update is not done in-place.
+
+### On top of the NES/Famicom
+
+The storage is covered via the 8KB battery-backed PRG-RAM that some chips
+allowed. In particular, here the MMC1 chip is being used just because it's the
+one that allows for this and it's simple enough. This chip allows for having a
+swappable bank, and here's where I've written my code, inside of the "LIBTREE"
+segment and on the `lib.s` file. There is no good reason to have the library
+into another segment, but it felt like a good way to have separation of
+concerns.
+
+In the context of operating systems, we would be manipulating at the page
+level. Out of simplicity here the same is done, the size of which will be the
+one native to the 6502 platform: 256B. Hence, on PRG-RAM we have 32 pages in
+total.
+
+## But, why?
+
+Just for fun :)
+
+## License
+
+Released under the [GPLv3+](http://www.gnu.org/licenses/gpl-3.0.txt), Copyright
+(C) 2026-<i>Ω</i> Miquel Sabaté Solà.
diff --git a/assets/btree.chr b/assets/btree.chr
new file mode 100644
index 0000000..6b06f77
--- /dev/null
+++ b/assets/btree.chr
diff --git a/assets/session.nss b/assets/session.nss
new file mode 100644
index 0000000..c170e67
--- /dev/null
+++ b/assets/session.nss
@@ -0,0 +1,620 @@
+NSTssTXT

+

+BtnTiles=1

+BtnChecker=0

+BtnSelTiles=0

+BtnChrBank1=1

+BtnChrBank2=0

+BtnChrBank3=0

+BtnChrBank4=0

+BtnGridAll=1

+BtnGridTile=0

+BtnGridAtr=1

+BtnGridBlock=0

+BtnGridScr=0

+BtnSelectedOnlyInverted=0

+BtnSolidityMask=0

+BtnPal=1

+BtnTypeIn=0

+BtnFrameAll=1

+BtnFrameSelected=0

+BtnFrameNone=0

+BtnSpriteSnap=0

+BtnSprite8x16=0

+BtnForce8x16=1

+MenuBestOffsets=0

+MenuLossy=0

+MenuThreshold=0

+MenuNoColorData=0

+MenuMetaSprAutoInc=0

+MenuMetaSprSkipZero=0

+MenuMetaSprMerge=0

+MenuSaveIncName=1

+MenuSaveIncAttr=1

+MenuSaveRLE=0

+CheckLinkedCHRmode=0

+CheckMetatileEditor_ReserveFirst=0

+CheckMetatileEditor_AlignToScreen=0

+BtnMetatileEditor_UseAttributes=0

+BtnMetatileEditor_Clonestamp=0

+BtnMetatileEditor_CloneSnap=0

+BtnMetatileEditor_Tiles=0

+BtnMetatileEditor_Attributes=0

+BtnMetatileEditor_Properties=0

+BtnMetatileEditor_Map=0

+ChkSwapBanks_Properties=0

+ChkSwapBanks_Labels=0

+BtnPPuMaskA=0

+BtnPPuMaskB=0

+BtnPPuMaskLinked=1

+VarNullTile=0

+VarBankActive_mapBuffer=0

+VarBankActive_msprBuffer=0

+VarPalBank_mapBuffer=0

+VarPalBank_msprBuffer=0

+VarTileViewTagBuf=0

+VarBgPalCur=3

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+VarTileActive=243

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+VarPalBank=0

+VarMetaSpriteActive=0

+VarSpriteActive=0

+VarSpriteGridX=64

+VarSpriteGridY=64

+VarNameW=32

+VarNameH=30

+VarNameViewX=0

+VarNameViewY=-1

+VarNameViewX2=0

+VarNameViewY2=-1

+VarNameSelectionL=-1

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+VarNameSelectionT=-1

+VarNameSelectionB=0

+VarNameCopyW=-1

+VarNameCopyH=-1

+VarCHRSelectionL=3

+VarCHRSelectionR=4

+VarCHRSelectionT=15

+VarCHRSelectionB=16

+VarCHRCopyW=-1

+VarCHRCopyH=-1

+VarCHRCopyRect=1

+VarCHRSelectRect=1

+VarCHRBanks=4

+VarCHRBanksUndo=4

+VarCheckpoint_CHRBanks=4

+VarCheckpoint_CHRBanksUndo=4

+VarMtClickID=0

+VarMtClickID_store_2x2=0

+VarMtClickID_store_4x4=0

+VarMtClickID_store_8x8=0

+VarMetatileSets_2x2=4

+VarUndo_metatileSets_2x2=4

+VarCheckpoint_metatileSets_2x2=4

+VarUndo_checkpoint_metatileSets_2x2=4

+VarMetatileSets_4x4=4

+VarUndo_metatileSets_4x4=4

+VarCheckpoint_metatileSets_4x4=4

+VarUndo_checkpoint_metatileSets_4x4=4

+VarMetatileSets_8x8=2

+VarUndo_metatileSets_8x8=2

+VarCheckpoint_metatileSets_8x8=2

+VarUndo_checkpoint_metatileSets_8x8=2

+VarCustomScanlineWarningCyan=2

+VarBrushPresetIndex=0

+BtnStateMtProps0=0

+BtnStateMtProps1=0

+BtnStateMtProps2=0

+BtnStateMtProps3=0

+BtnStateMtProps4=0

+BtnStateMtProps5=0

+BtnStateMtProps6=0

+BtnStateMtProps7=0

+BtnStateCHRProps0=0

+BtnStateCHRProps1=0

+BtnStateCHRProps2=0

+BtnStateCHRProps3=0

+BtnStateCHRProps4=0

+BtnStateCHRProps5=0

+BtnStateCHRProps6=0

+BtnStateCHRProps7=0

+propertyCHRlabel0=solid

+propertyCHRlabel1=dangerous

+propertyCHRlabel2=unlabeled2

+propertyCHRlabel3=unlabeled3

+propertyCHRlabel4=unlabeled4

+propertyCHRlabel5=unlabeled5

+propertyCHRlabel6=escape bit

+propertyCHRlabel7=global condition

+

+

+

+MetaSpriteBankName=session

+MetaspritePlayBackCursor=0

+

+

+FilterCHR=1

+FilterName=1

+FileNameCHR=C:\users\mssola\Desktop\src\git.mssola.com\public\nes\btree.nes\assets\btree

+FileNameName=

+FileNamePal=

+FileNameMetaSpriteBank=

+FileNameTileProps=

+FileNameMetatileText=

+FileNameAssociatedMetatiles=

+FileNameAssociatedTileset=

+CheckboxDoAssociateMetatiles=0

+CheckboxDoAssociateTileset=0

+RadioAutoexport_UseWorkDir=0

+RadioAutoexport_UseSubDir_Project=0

+RadioAutoexport_UseSubDir_NEXXT=0

+CheckAutoexport_MetatileAsBMP=0

+

+

+VarCHRSelected=00[f3]0100[c]

+

+

+Palette=0f0010300f0c21320f0516270f0b1a290f1c21320f1122330f1223340f1324350f1324360f1526370f1627370f1928380f1829380f1b2a390f1b2b3c0f1c2c3b

+

+

+PalUndo=0f0010300f0c21320f0516270f0b1a290f1c21320f1122330f1223340f1324350f1324360f1526370f1627370f1928380f1829380f1b2a390f1b2b3c0f1c2c3b

+

+

+CHRMain=00[101]3c464a52623c00[a]182808[3]3e00[a]3c42023c407e00[a]3c420c02423c00[a]081828487e0800[a]7e407c02423c00[a]3e407c42[2]3c00[a]3e02040810[2]00[a]3c423c42[2]3c00[a]3c42[2]3e023c00[9]3c4299a1[2]99423c00[9]3c42[2]7e42[2]00[a]7c427c42[2]3c00[a]3c4240[2]423c00[a]7c42[4]7c00[a]7c407040[2]7c00[a]3c40[2]7040[2]00[a]3c42404e423c00[a]42[3]7e42[2]00[a]3e08[4]3e00[a]02[3]42[2]3c00[a]44487048444200[a]40[5]7e00[a]42665a42[3]00[a]4262524a464200[a]3c42[4]3c00[a]7c42[2]7c40[2]00[a]3c42[3]3c0600[a]3c42[2]7c444200[a]3e403c02[2]7c00[a]3e08[5]00[a]42[5]3c00[a]22[4]140800[a]42[3]5a664200[a]422418[2]244200[a]41221408[3]00[a]7e040810207e00[9]3c4299a5[2]9f423c00[3ca8]

+

+

+CHRUndo=00[101]3c464a52623c00[a]182808[3]3e00[a]3c42023c407e00[a]3c420c02423c00[a]081828487e0800[a]7e407c02423c00[a]3e407c42[2]3c00[a]3e02040810[2]00[a]3c423c42[2]3c00[a]3c42[2]3e023c00[9]3c4299a1[2]99423c00[9]3c42[2]7e42[2]00[a]7c427c42[2]3c00[a]3c4240[2]423c00[a]7c42[4]7c00[a]7c407040[2]7c00[a]3c40[2]7040[2]00[a]3c42404e423c00[a]42[3]7e42[2]00[a]3e08[4]3e00[a]02[3]42[2]3c00[a]44487048444200[a]40[5]7e00[a]42665a42[3]00[a]4262524a464200[a]3c42[4]3c00[a]7c42[2]7c40[2]00[a]3c42[3]3c0600[a]3c42[2]7c444200[a]3e403c02[2]7c00[a]3e08[5]00[a]42[5]3c00[a]22[4]140800[a]42[3]5a664200[a]422418[2]244200[a]41221408[3]00[a]7e040810207e00[9]3c4299a5[2]9f423c00[cb9]c000[4]e000[2]c000f070[2]e0002b3f01[2]03[3]002b3f01[2]03[3]00e0[2]d0a030b8fc00e0[2]d0a030b8fc0001[2]02[2]05[2]090801[2]02[2]05[2]090880[2]c0[2]e0[2]f01080[2]c0[2]e0[2]f01009[5]19[2]2909[5]19[2]2910f0b030b018f8fc10f0b030b018f8fcb9[3]f9a9[2]f4f5b9[3]f9a9[2]f4f5f7[2]fff5[3]6feff7[2]fff5[3]6fef00[2]3c3f7f7c7d[2]071f3f7ffffcfd[2]00[3]e0f038[2]bce0f8fcfeff3fbf[2]00[c]18ff[2]8a00[c]18ff[2]8bff[2]00[16]ff[2]00[16]c068[2]1ce0[4]c068[2]1ce0[4]2a3d070f667038002a3d070f66703800e060[3]70787c00e060[3]70787c0009[10]f0[5]50[3]f0[5]50[3]2959[2]89b9[4]2959[2]89b9[4]fcf4f6[2]f1f7[3]fcf4f6[2]f1f7[3]555289b9b858a850555289b9b800[3]eacb9197171a150aeacb91971700[3]7c7f[2]3f[3]00[2]fcfff17c7f[2]3f073efef8fcf0e000[2]3fffe71efc[2]f8e000[8]ba8abab8ff[2]1800[9]bb9bbb89ff[2]1800ff[2]00[6]ff[2]00[26]e0[2]c000c0e0f000e0[2]c000c0e0f0002a3e00281c206c102a3e00[6]f0[2]3000383c00[2]f0[2]3000383c00[3]071f3f7f[2]ff[2]00071f3f7f[2]ff[2]00e0f89c8ec6e7[2]00e0f89c8ec6e7[2]00[2]092e4f33f1fc00[2]092e4f33f1fc00[3]2080e4f07400[3]2080e4f07400121a6b5f3ff93600121a6b5f3ff936004094eafffe9f6c004094eafffe9f6c00[3]031ffcff0300[3]031ffcff0308[2]7cfe8301ff5108[2]7cfe8301ff51030607[2]047b94d5030607[2]047b94d58040[2]c040bc525a8040[2]c040bc525a0c1f13[2]3f4cd0df0c1f13[2]3f4cd0df60f098[2]f46e9fff60f098[2]f46e9fff00[13]1f6ff7031f00[3]1f6ff7031f003ef8f3ffdfe3f8003ef8f3ffdfe3f800[10]ff[2]7f[2]3f1f0700ff[2]7f[2]3f1f0700ff[2]fe[2]fcf8e000ff[2]fe[2]fcf8e000f1c7797531190e00f1c7797531190e00d6e1e4f2b8402000d6e1e4f2b8402000f6793f4d0f160a00f6793f4d0f160a006e9ffefdf4e844006e9ffefdf4e8440003fffc1f0300[3]03fffc1f0300[3]51ff0183fe7c08[2]51ff0183fe7c08[2]f47b040704070300f47b0407040703005ebc40c040[2]80005ebc40c040[2]8000df7f3f130c00[3]df7f3f130c00[3]fffefcc83000[3]fffefcc83000[13]80e0b0fcfe9bfefc80e0b0fcfe9bfefc00[20]071f3f7f[2]ff[3]071f3f7f[2]ff[3]e0f8fc9e8ec7e7[2]e0f8fc9e8ec7e7[2]00[2]082e4f33f1fc00[2]082e4f33f1fc00[2]801088e2f07600[2]801088e2f07600022957ff7ff93600022957ff7ff936004858d6fafc9f6c004858d6fafc9f6c00[3]031ffcff0f00[3]031ffcff0b08[2]7cfe8331ff4508[2]7cfe8331ff4503040507047b94b503040507047b94b580c0[3]40bc525680c0[3]40bc5256060f19[2]2f76f9ff060f19[2]2f76f9ff30f8c8[2]fc320bfb30f8c8[2]fc320bfb00[10]80e0b0fcfe73fefc80e0b0fcfe73fefc00[20]ff[3]7f[2]3f1f07ff[3]7f[2]3f1f07ff[3]fe[2]fcf8e0ff[3]fe[2]fcf8e0f1c7797531190e00f1c7797531190e00d2e0e4f2b900a410d2e0e4f2b900a41076f97fbf2f17220076f97fbf2f1722006f9efcb2f06850006f9efcb2f06850000ffffc1f0300[3]0bfffc1f0300[3]45ff3183fe7c08[2]45ff3183fe7c08[2]f47b040704050300f47b0407040503005ebc40c040c080005ebc40c040c08000ff7f3f130c00[3]ff7f3f130c00[3]fbfefcc83000[3]fbfefcc83000[14]3ef8f3ffdfe3f8003ef8f2fcdce2f800[2]0304050f0b1000[2]0304050f0b1000[2]80c0[2]e0a01000[2]80c0[2]e0a01000[4]1f20489c00[4]1f20489c00[4]f008247200[4]f008247200[3]071f3f5f8f00[b]80e0f0e8c400[e]0f3800[6]0f3800[6]f03c00[6]f03c00[7]0f00[7]0f00[7]e000[7]e000[53]c0e0f0f878002000[2]0400[2]8010207098bff8700010207098bff8700010081c26ee3e1c0010081c26ee3e1c00de41c18347201f00de41c18347201f00f6040682c408f000f6040682c408f000d0703f1f0f070300[9]2c38f0e0c08000[a]60c3c7cfff7f3f0060c3c7cfff7f3f007eff[4]fefc007eff[4]fefc001f3f2040[2]80ff001f3f2040[2]80ff00b078fc7c7838f000b078fc7c7838f000[51]78f8f0e0c000[3]8000[5]2000[23]01[2]03[2]070900[2]01[2]03[2]070970f8e4[6]70f8e4[6]16[2]1a16[2]17[2]1a16[2]1a16[2]17[2]1ab4[2]a4ac2cec[2]2cb4[2]a4ac2cec[2]2c1a16366e[2]af[3]1a16366e[2]af[3]ec[4]fc[2]3844ec[4]fc[2]384400[72]e0f0f8bc5c3c0008040200402000[21]090f19[2]1f[2]17[2]090f19[2]1f[2]17[2]f4[10]1716[3]1f[2]18161716[3]1f[2]1816ac2cec2cec[2]f8ecac2cec2cec[2]f8ecae[3]be[2]800001ae[3]be[2]8000[2]5c429e[3]deaa755c429e[3]00[73]3c5c1cf8f0e000[3]20e000[2]020600[21]01[4]0205080901[4]0205080980[4]40e010f080[4]40e010f0d9[2]a6[2]ff8b[2]8ad9[2]a6[2]ff8b[2]8a9b[2]65[2]ff[3]d19b[2]65[2]ff[3]d1a6[2]7f45[4]7fa6[2]7f45[4]7f65[2]fe[6]65[2]fe[6]00[72]e0380c04060204080100[4]6000[20]09[2]1e1325[2]4b7f09[2]1e1325[2]4b7ff0[2]08f8fc[2]fe[2]f0[2]08f8fc[2]fe[2]8a[4]8bffd9[2]8a[4]8bffd9[2]ddd1dd11ff[2]9b98ddd1dd11ff[2]9b98285c[2]829ed6aa54285c[2]829e00[3]142e[2]414f6b552a142e[2]414f00[73]0206040c38e000[2]8000[3]0100080400[20]01[2]03[3]0705[2]01[2]03[3]0705[2]80[2]c0[3]e0a0[2]80[2]c0[3]e0a0[2]1911191d1f[3]0f1911191d1f[3]0f88[2]98b8f8[3]f088[2]98b8f8[3]f0bbfbab[3]8bfbf3bbfbab[3]8bfbf3dddfd7dfd5d1ddcfdddfd7dfd5d1ddcf00[a0]0d09[2]1b151913150d09[2]1b15191315b090[2]9888[4]b090[2]9888[4]8f[3]97[3]bb[2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+

+

+CHRCopy=00[4000]

+

+

+NameTable=00[3c0]

+

+

+NameCopy=00[3c0]

+

+

+NameUndo=00[3c0]

+

+

+AttrTable=00[40]

+

+

+AttrCopy=00[40]

+

+

+AttrUndo=00[40]

+

+

+MetaSprites=ff[10000]

+

+

+iBrushSize=02030405

+

+

+iBrushSnapSize_x=02030405

+

+

+iBrushSnapSize_y=02030405

+

+

+iBrushCursorAlignment=04[4]

+

+

+BrushMask_2a=01[100]

+

+

+BrushMask_3a=000100010001000100[2]010001000100[2]0100010001000100[2]010001000100[2]0100010001000100[2]010001000100[2]0100010001000100[2]010001000100[2]0100010001000100[2]010001000100[2]0100010001000100[2]010001000100[2]0100010001000100[2]010001000100[2]0100010001000100[2]010001000100[2]0100010001000100[2]010001000100[2]0100010001000100[2]010001000100[2]0100010001000100[2]010001000100[2]0100010001000100[2]010001000100[2]0100010001000100[2]010001000100[2]0100010001000100[2]010001000100[2]0100010001000100[2]010001000100[2]0100010001000100[2]010001000100

+

+

+BrushMask_4a=0001[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00[2]01[2]00

+

+

+BrushMask_5a=0001[3]00[2]01[3]00[2]01[3]00[3]01[3]00[2]01[3]00[2]01[3]00[3]01[3]00[2]01[3]00[2]01[3]00[3]01[3]00[2]01[3]00[2]01[3]00[3]01[3]00[2]01[3]00[2]01[3]00[3]01[3]00[2]01[3]00[2]01[3]00[3]01[3]00[2]01[3]00[2]01[3]00[3]01[3]00[2]01[3]00[2]01[3]00[3]01[3]00[2]01[3]00[2]01[3]00[3]01[3]00[2]01[3]00[2]01[3]00[3]01[3]00[2]01[3]00[2]01[3]00[3]01[3]00[2]01[3]00[2]01[3]00[3]01[3]00[2]01[3]00[2]01[3]00[3]01[3]00[2]01[3]00[2]01[3]00[3]01[3]00[2]01[3]00[2]01[3]00[3]01[3]00[2]01[3]00[2]01[3]00[2]

+

+

+BrushMask_6a=01[100]

+

+

+BrushMask_7a=01[100]

+

+

+BrushMask_8a=01[100]

+

+

+BrushMask_2b=00[5]01[6]00[8]01[2]00[6]01[2]00[5]0100[a]0100[3]0100[c]0100[2]0100[c]01000100[e]01[2]00[e]01[2]00[e]01[2]00[e]01[2]00[e]01[2]00[e]01000100[c]0100[2]0100[c]0100[3]0100[a]0100[5]01[2]00[6]01[2]00[8]01[6]00[5]

+

+

+BrushMask_3b=000100[e]01[3]00[e]0100[de]

+

+

+BrushMask_4b=0001[2]00[d]01[4]00[c]01[4]00[d]01[2]00[cd]

+

+

+BrushMask_5b=0001[3]00[c]01[5]00[b]01[5]00[b]01[5]00[c]01[3]00[bc]

+

+

+BrushMask_6b=00[2]01[2]00[d]01[4]00[b]01[6]00[a]01[6]00[b]01[4]00[d]01[2]00[ac]

+

+

+BrushMask_7b=00[2]01[3]00[c]01[5]00[a]01[7]00[9]01[7]00[9]01[7]00[a]01[5]00[c]01[3]00[9b]

+

+

+BrushMask_8b=00[2]01[4]00[b]01[6]00[9]01[8]00[8]01[8]00[8]01[8]00[8]01[8]00[9]01[6]00[b]01[4]00[8a]

+

+

+32_BankViewTable=00000000[100]00001000[100]00002000[100]00003000[100]

+

+

+32_BankViewTableUndo=00000000[100]00001000[100]00002000[100]00003000[100]

+

+

+8_TileCollisionProperties=00[400]

+

+

+8_TileCollisionPropertiesUndo=00[400]

+

+

+PropertyConditions=1[2]0[2]1[2]0[2]1[2]0[2]1[2]0[2]1[2]0[2]1[2]0[2]1[2]0[2]1[2]0[2]

+

+

+PropertyConditionsUndo=1[2]0[2]1[2]0[2]1[2]0[2]1[2]0[2]1[2]0[2]1[2]0[2]1[2]0[2]1[2]0[2]

+

+

+TilePropConditionType=00[7]02

+

+

+TilePropConditionTypeUndo=00[7]02

+

+

+MetatileSet_2x2_id=00[400]

+

+

+MetatileSet_2x2_idUndo=00[400]

+

+

+MetatileSet_2x2_pal=00[400]

+

+

+MetatileSet_2x2_palUndo=00[400]

+

+

+MetatileSet_2x2_props=00[400]

+

+

+MetatileSet_2x2_propsUndo=00[400]

+

+

+MetatileSet_4x4_id=00[1000]

+

+

+MetatileSet_4x4_idUndo=00[1000]

+

+

+MetatileSet_4x4_pal=00[1000]

+

+

+MetatileSet_4x4_palUndo=00[1000]

+

+

+MetatileSet_4x4_props=00[1000]

+

+

+MetatileSet_4x4_propsUndo=00[1000]

+

+

+MetatileSet_8x8_id=00[2000]

+

+

+MetatileSet_8x8_idUndo=00[2000]

+

+

+MetatileSet_8x8_pal=00[2000]

+

+

+MetatileSet_8x8_palUndo=00[2000]

+

+

+MetatileSet_8x8_props=00[2000]

+

+

+MetatileSet_8x8_propsUndo=00[2000]

+

+

+MetatileSetLabels_2x2=Unlabeled,Unlabeled,Unlabeled,Unlabeled

+MetatileSetLabels_2x2Undo=Unlabeled,Unlabeled,Unlabeled,Unlabeled

+

+MetatileSetLabels_4x4=Unlabeled,Unlabeled,Unlabeled,Unlabeled

+MetatileSetLabels_4x4Undo=Unlabeled,Unlabeled,Unlabeled,Unlabeled

+

+MetatileSetLabels_8x8=Unlabeled,Unlabeled

+MetatileSetLabels_8x8Undo=Unlabeled,Unlabeled

+

+CHRBankLabels=Unlabeled,Unlabeled,Unlabeled,Unlabeled

+

+CHRBankLabelsUndo=Unlabeled,Unlabeled,Unlabeled,Unlabeled

+

+32_NTSC_MsprDuration=00000006[100]

+

+

+32_NTSC_MsprDurationUndo=00000006[100]

+

+

+32_PAL_MsprDuration=00000005[100]

+

+

+32_PAL_MsprDurationUndo=00000005[100]

+

+

+MsprDirectTagStart=0[100]

+

+

+MsprDirectTagStartUndo=0[100]

+

+

+MsprDirectTagLoop=0[100]

+

+

+MsprDirectTagLoopUndo=0[100]

+

+

+MsprDirectTagCall=0[100]

+

+

+MsprDirectTagCallUndo=0[100]

+

+

+MsprDirectTagCall2=0[100]

+

+

+MsprDirectTagCall2Undo=0[100]

+

+

+MsprDirectTagRevert=0[100]

+

+

+MsprDirectTagRevertUndo=0[100]

+

+

+MsprDirectTagSeconds=0[100]

+

+

+MsprDirectTagSecondsUndo=0[100]

+

+

+MsprDirectTagHalfSeconds=0[100]

+

+

+MsprDirectTagHalfSecondsUndo=0[100]

+

+

+Checkpoint_Palette=0f0010300f0c21320f0516270f0b1a290f1c21320f1122330f1223340f1324350f1324360f1526370f1627370f1928380f1829380f1b2a390f1b2b3c0f1c2c3b

+

+

+Checkpoint_PalUndo=0f0010300f0c21320f0516270f0b1a290f1c21320f1122330f1223340f1324350f1324360f1526370f1627370f1928380f1829380f1b2a390f1b2b3c0f1c2c3b

+

+

+Checkpoint_CHRMain=00[4000]

+

+

+Checkpoint_CHRUndo=00[4000]

+

+

+Checkpoint_NameTable=00[3c0]

+

+

+Checkpoint_NameUndo=00[3c0]

+

+

+Checkpoint_AttrTable=00[40]

+

+

+Checkpoint_AttrUndo=00[40]

+

+

+Checkpoint_MetaSprites=ff[10000]

+

+

+Checkpoint_32_BankViewTable=00000000[100]00001000[100]00002000[100]00003000[100]

+

+

+Checkpoint_32_BankViewTableUndo=00000000[100]00001000[100]00002000[100]00003000[100]

+

+

+Checkpoint_8_TileCollisionProperties=00[400]

+

+

+Checkpoint_8_TileCollisionPropertiesUndo=00[400]

+

+

+Checkpoint_PropertyConditions=0[20]

+

+

+Checkpoint_PropertyConditionsUndo=0[20]

+

+

+Checkpoint_TilePropConditionType=00[7]02

+

+

+Checkpoint_TilePropConditionTypeUndo=00[7]02

+

+

+Checkpoint_MetatileSet_2x2_id=00[400]

+

+

+Checkpoint_MetatileSet_2x2_idUndo=00[400]

+

+

+Checkpoint_MetatileSet_2x2_pal=00[400]

+

+

+Checkpoint_MetatileSet_2x2_palUndo=00[400]

+

+

+Checkpoint_MetatileSet_2x2_props=00[400]

+

+

+Checkpoint_MetatileSet_2x2_propsUndo=00[400]

+

+

+Checkpoint_MetatileSet_4x4_id=00[1000]

+

+

+Checkpoint_MetatileSet_4x4_idUndo=00[1000]

+

+

+Checkpoint_MetatileSet_4x4_pal=00[1000]

+

+

+Checkpoint_MetatileSet_4x4_palUndo=00[1000]

+

+

+Checkpoint_MetatileSet_4x4_props=00[1000]

+

+

+Checkpoint_MetatileSet_4x4_propsUndo=00[1000]

+

+

+Checkpoint_MetatileSet_8x8_id=00[2000]

+

+

+Checkpoint_MetatileSet_8x8_idUndo=00[2000]

+

+

+Checkpoint_MetatileSet_8x8_pal=00[2000]

+

+

+Checkpoint_MetatileSet_8x8_palUndo=00[2000]

+

+

+Checkpoint_MetatileSet_8x8_props=00[2000]

+

+

+Checkpoint_MetatileSet_8x8_propsUndo=00[2000]

+

+

+Checkpoint_MetatileSetLabels_2x2=Unlabeled,Unlabeled,Unlabeled,Unlabeled

+Checkpoint_MetatileSetLabels_2x2Undo=Unlabeled,Unlabeled,Unlabeled,Unlabeled

+

+Checkpoint_MetatileSetLabels_4x4=Unlabeled,Unlabeled,Unlabeled,Unlabeled

+Checkpoint_MetatileSetLabels_4x4Undo=Unlabeled,Unlabeled,Unlabeled,Unlabeled

+

+Checkpoint_MetatileSetLabels_8x8=Unlabeled,Unlabeled

+Checkpoint_MetatileSetLabels_8x8Undo=Unlabeled,Unlabeled

+

+Checkpoint_CHRBankLabels=Unlabeled,Unlabeled,Unlabeled,Unlabeled

+

+Checkpoint_CHRBankLabelsUndo=Unlabeled,Unlabeled,Unlabeled,Unlabeled

+

+

+Checkpoint_32_NTSC_MsprDuration=00000006[100]

+

+

+Checkpoint_32_NTSC_MsprDurationUndo=00000000[100]

+

+

+Checkpoint_32_PAL_MsprDuration=00000005[100]

+

+

+Checkpoint_32_PAL_MsprDurationUndo=00000000[100]

+

+

+Checkpoint_MsprDirectTagStart=0[100]

+

+

+Checkpoint_MsprDirectTagStartUndo=0[100]

+

+

+Checkpoint_MsprDirectTagLoop=0[100]

+

+

+Checkpoint_MsprDirectTagLoopUndo=0[100]

+

+

+Checkpoint_MsprDirectTagCall=0[100]

+

+

+Checkpoint_MsprDirectTagCallUndo=0[100]

+

+

+Checkpoint_MsprDirectTagCall2=0[100]

+

+

+Checkpoint_MsprDirectTagCall2Undo=0[100]

+

+

+Checkpoint_MsprDirectTagRevert=0[100]

+

+

+Checkpoint_MsprDirectTagRevertUndo=0[100]

+

+

+Checkpoint_MsprDirectTagSeconds=0[100]

+

+

+Checkpoint_MsprDirectTagSecondsUndo=0[100]

+

+

+Checkpoint_MsprDirectTagHalfSeconds=0[100]

+

+

+Checkpoint_MsprDirectTagHalfSecondsUndo=0[100]

+

+=========================================================

+Current settings switch tiles

+=========================================================

+

+

+

+Metadata:

+---------------------------------------------------------

+Switch tiles enabled=0

+Current preset ID=0

+

+GUI behaviour:

+---------------------------------------------------------

+Use paired mode if possible=1

+Affect backgrounds=1

+Affect sprites=1

+

+Nonpaired mode start set behaviour:

+---------------------------------------------------------

+Nonpaired, Use set of 1st checked switch tile=1

+Nonpaired, Use active set=0

+Nonpaired, Use fixed set=0

+Nonpaired, fixed set ID=0

+

+Paired mode start set behaviour:

+---------------------------------------------------------

+Paired, Use set of 1st checked switch tile=1

+

+Switch tile IDs:

+---------------------------------------------------------

+Switch tile 1 ID=254

+Switch tile 2 ID=253

+Switch tile 3 ID=252

+Switch tile 4 ID=251

+

+Switch tile targets:

+---------------------------------------------------------

+Switch tile 1 target=4096

+Switch tile 2 target=0

+Switch tile 3 target=12288

+Switch tile 4 target=8192

+

+Switch tile checkboxes:

+---------------------------------------------------------

+Switch tile 1 checkbox=1

+Switch tile 2 checkbox=1

+Switch tile 3 checkbox=0

+Switch tile 4 checkbox=0

diff --git a/config/mmc1.cfg b/config/mmc1.cfg
new file mode 100644
index 0000000..4803993
--- /dev/null
+++ b/config/mmc1.cfg
@@ -0,0 +1,22 @@
+MEMORY {
+    # iNES header.
+    HEADER: start = $0, size = $10, fill = yes;
+
+    # Banked PRG ROM: one for the NES game, the other for the library.
+    PRG0: start = $8000, size = $4000, fill = yes, fillval = $00, define = yes;
+    PRG1: start = $C000, size = $3FFA, fill = yes, fillval = $01, define = yes;
+
+    # Hardware Vectors.
+    ROMV: start = $FFFA, size = $0006, fill = yes;
+
+    # No banking on CHR, we keep it simple.
+    ROM2: start = $0000, size = $2000, fill = yes, fillval = $02;
+}
+
+SEGMENTS {
+    HEADER:  load = HEADER, type = ro;
+    FIXED:   load = PRG0, type = ro;
+    LIBTREE: load = PRG1, type = ro;
+    VECTORS: load = ROMV, type = ro;
+    CHARS:   load = ROM2, type = ro;
+}
\ No newline at end of file
diff --git a/include/apu.s b/include/apu.s
new file mode 100644
index 0000000..8a23c49
--- /dev/null
+++ b/include/apu.s
@@ -0,0 +1,4 @@
+.scope APU
+    m_dmc               = $4010
+    m_frame_counter     = $4017
+.endscope
diff --git a/include/asm.s b/include/asm.s
new file mode 100644
index 0000000..f5d39bc
--- /dev/null
+++ b/include/asm.s
@@ -0,0 +1,9 @@
+;; Pseudo-instruction from 'nasm' that is not available for 'ca65'. An empty
+;; implementation is actually quite accurate, as it's just a way for 'nasm' to
+;; perform extra checks when programmers want to explicitly make the code fall
+;; through.
+.ifndef __NASM__
+    .macro __fallthrough__ arg
+        ;; Nothing to do.
+    .endmacro
+.endif
diff --git a/include/mmc1.s b/include/mmc1.s
new file mode 100644
index 0000000..3a6bc5d
--- /dev/null
+++ b/include/mmc1.s
@@ -0,0 +1,5 @@
+.scope MMC1
+    m_control  = $8000
+    m_chr_bank = $A000
+    m_prg_bank = $E000
+.endscope
diff --git a/include/oam.s b/include/oam.s
new file mode 100644
index 0000000..a73494d
--- /dev/null
+++ b/include/oam.s
@@ -0,0 +1,12 @@
+.scope OAM
+    ;; Region in internal RAM where sprites are being allocated for later use in
+    ;; the DMA process. The entire page is reserved, as there are 64 sprites x 4
+    ;; bytes each = 256 bytes in total.
+    m_sprites = $200            ; asan:reserve $100
+
+    ;;;
+    ;; Actual addresses from OAM space.
+
+    m_address = $2003
+    m_dma     = $4014
+.endscope
diff --git a/include/ppu.s b/include/ppu.s
new file mode 100644
index 0000000..dbef40e
--- /dev/null
+++ b/include/ppu.s
@@ -0,0 +1,6 @@
+.scope PPU
+    m_control = $2000
+    m_mask    = $2001
+    m_status  = $2002
+    m_scroll  = $2005
+.endscope
diff --git a/src/btree.s b/src/btree.s
new file mode 100644
index 0000000..2867bf0
--- /dev/null
+++ b/src/btree.s
@@ -0,0 +1,132 @@
+.segment "HEADER"
+    .byte 'N', 'E', 'S', $1A
+
+    ;; We split the PRG-ROM into two 16KB sections, the first fixed (the game
+    ;; itself), and then the second one, which holds the library.
+    .byte $02
+
+    ;; We keep the CHR-ROM simple: the most basic one (8KB) and no windows.
+    .byte $01
+
+    ;; - bit 1: contains battery-backed PRG RAM ($6000-7FFF)
+    ;; - bit 7-4: the lower nibble of the mapper (#%0001 for MMC1)
+    .byte $12
+
+    ;; Blanked out stuff.
+    .res $09, $00
+
+;; asan:fixed-segments FIXED, LIBTREE
+.segment "FIXED"
+.asciiz "@mssola"
+
+.include "../include/apu.s"
+.include "../include/oam.s"
+.include "../include/ppu.s"
+.include "../include/mmc1.s"
+.include "../include/asm.s"
+
+.include "lib.s"
+.include "interrupts.s"
+
+.proc reset
+    ;; Disable interrupts and decimal mode.
+    sei
+    cld
+
+    ;; Disable APU frame counter.
+    ldx #$40
+    stx APU::m_frame_counter
+
+    ;; Setup the stack.
+    ldx #$FF
+    txs                         ; asan:stack $80-$FF
+
+    ;; Disable NMIs and the APU's DMC.
+    inx
+    stx PPU::m_control
+    stx PPU::m_mask
+    stx APU::m_dmc
+
+    ;; Reset MMC1 chip.
+reset_mmc1:
+    inc reset_mmc1
+
+    ;; First PPU wait.
+    bit PPU::m_status
+@vblankwait1:
+    bit PPU::m_status
+    bpl @vblankwait1
+
+    ;; Reset all sprites by simply moving the Y coordinate out of screen.
+    lda #$EF
+    ldx #0
+@sprite_reset_loop:
+    sta OAM::m_sprites, x
+    inx
+    inx
+    inx
+    inx
+    bne @sprite_reset_loop
+
+    ;; DMA setup for sprite reset.
+    lda #$00
+    sta OAM::m_address
+    lda #$02
+    sta OAM::m_dma
+
+    ;; Second PPU wait. After that the PPU is stable.
+@vblankwait2:
+    bit PPU::m_status
+    bpl @vblankwait2
+
+    ;;;
+    ;; Configure the MMC1 chip.
+
+    ;; The control register:
+    ;;
+    ;;  - bits 0-1: nametable arrangement: horizontal mirroring.
+    ;;  - bits 2-3: PRG-ROM fixed at $8000 (game), swappable at $C000 (library).
+    ;;  - bit 4:    CHR-ROM: 8KB at a time.
+    lda #%00001011
+    sta MMC1::m_control
+    lsr
+    sta MMC1::m_control
+    lsr
+    sta MMC1::m_control
+    lsr
+    sta MMC1::m_control
+    lsr
+    sta MMC1::m_control
+
+    ;; CHR bank: 0.
+    lda #0
+    sta MMC1::m_chr_bank
+    sta MMC1::m_chr_bank
+    sta MMC1::m_chr_bank
+    sta MMC1::m_chr_bank
+    sta MMC1::m_chr_bank
+
+    ;; The swappable bank is 1, which contains the library. Also set PRG-RAM to
+    ;; be enabled.
+    lda #1
+    sta MMC1::m_prg_bank
+    sta MMC1::m_prg_bank
+    sta MMC1::m_prg_bank
+    sta MMC1::m_prg_bank
+    sta MMC1::m_prg_bank
+
+    __fallthrough__ main
+.endproc
+
+.proc main
+    jsr Btree::todo
+
+@tbd:
+    jmp @tbd
+.endproc
+
+.segment "VECTORS"
+.addr nmi, reset, irq
+
+.segment "CHARS"
+.incbin "../assets/btree.chr"
diff --git a/src/interrupts.s b/src/interrupts.s
new file mode 100644
index 0000000..be276df
--- /dev/null
+++ b/src/interrupts.s
@@ -0,0 +1,37 @@
+.segment "FIXED"
+
+.proc nmi
+    pha
+    txa
+    pha
+    tya
+    pha
+
+    ;; Sprite DMA.
+    lda #$00
+    sta OAM::m_address
+    lda #$02
+    sta OAM::m_dma
+
+    ;; TODO
+
+    ;; Always reset the scroll just in case.
+    bit PPU::m_status
+    lda #$00
+    sta PPU::m_scroll
+    sta PPU::m_scroll
+
+    ;; Restore registers.
+    pla
+    tay
+    pla
+    tax
+    pla
+
+    rti
+.endproc
+
+;; Unused.
+.proc irq
+    rti
+.endproc
diff --git a/src/lib.s b/src/lib.s
new file mode 100644
index 0000000..64effd0
--- /dev/null
+++ b/src/lib.s
@@ -0,0 +1,7 @@
+.segment "LIBTREE"
+
+.scope Btree
+    .proc todo
+        rts
+    .endproc
+.endscope