N20: Reverse-Engineering NES Tetris to add Hard Drop

Author: gridbugs

content/posts/newsletter-020/index.md

@@ -68,6 +68,35 @@ If needed, a section can be split into subsections with a "------" delimiter.
 
 ## Learning Material Updates
 
+### [Reverse-Engineering NES Tetris to add Hard Drop][tetris-hard-drop]
+
+![NES Tetris with Hard Drop and Ghost Piece](tetris-hard-drop.gif)
+_NES Tetris with Hard Drop and Ghost Piece_
+
+A [blog post][tetris-hard-drop] describing the process of reverse-engineering
+the rendering and input-handling logic in the NES version of Tetris, and using
+a [rust embedded domain-specific language][tetris-hard-drop-dsl-example] to
+make a [patching tool][tetris-hard-drop-patch-tool] that
+generates code (6502 machine code) to add hard drop (instantly dropping the
+current piece) and to render a ghost piece (the dotted outline showing where
+the current piece will land).
+
+The patching tool uses the crate [mos6502_assembler][tetris-hard-drop-assembler] to specify 6502 assembly
+in rust and generate machine code. Many of the reverse-engineering experiments were done using
+[this rust NES emulator][tetris-hard-drop-nes-emulator].
+The result is available as an [IPS Patch][tetris-hard-drop-ips-patch].
+
+_Discussions:
+[Hacker News](https://news.ycombinator.com/item?id=26530604),
+[/r/rust](https://reddit.com/r/rust/comments/ma6jqz/using_a_rust_dsl_to_add_hard_drop_to_nes_tetris/)_
+
+[tetris-hard-drop]: https://www.gridbugs.org/reverse-engineering-nes-tetris-to-add-hard-drop/
+[tetris-hard-drop-nes-emulator]: https://github.com/stevebob/mos6502/tree/master/nes-emulator
+[tetris-hard-drop-assembler]: https://github.com/stevebob/mos6502/tree/master/assembler
+[tetris-hard-drop-ips-patch]: https://github.com/stevebob/mos6502/raw/master/tetris-hard-drop-patcher/tetris-hard-drop.ips
+[tetris-hard-drop-patch-tool]: https://github.com/stevebob/mos6502/tree/master/tetris-hard-drop-patcher
+[tetris-hard-drop-dsl-example]: https://github.com/stevebob/mos6502/blob/master/tetris-hard-drop-patcher/src/main.rs#L23
+
 ## Library & Tooling Updates
 
 ## Popular Workgroup Issues in Github