Starting a blog!
Published:
I figured it would be fun to keep a record of all the projects I’m working on in a blog format, so I’ve set up the blog page on my website! You’ll be able to access this page at any time by going to ahl27.com/blog!
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Refactoring R’s dendrapply
15 minute read
Published:
As someone who specializes in comparative phylogenomics, I work a lot with phylogenetic trees. Trees are represented in R as dendrogram objects, which are essentially a series of nested lists. Each “node” of the tree is a list with multiple members (two if a binary tree, but dendrogram objects are not constrained to be binary), each of which is another dendrogram object. The leaves are special cases in that they have length 1 and an additional property leaf, which is set to TRUE.
Finishing the 6502 Emulator
1 minute read
Published:
This will be a short blog post–I’ve officially finished v1.0.0 of my 65c02 emulator. Since last time, I’ve fixed a bunch of bugs, finished implementing the 65C02 extended opcode set (including the Rockwell/WDC bit set/clear instructions and test-and-branch instructions), and wrote assembly scripts to test the implementation of (nearly) all the opcodes. The only ones I haven’t thoroughly checked are the Rockwell/WDC extended instructions (e.g. RMB0, SMB0, BBR0, BBS0). I’ve also updated the GUI to graphically iterate through instructions when (r)un is input, meaning you can set up an infinite loop and watch it iterate through. The iteration executes at the same speed the computer normally would (determined by the clock speed), so you can watch it step through programs at slow speeds if you’d like.
Writing a 6502 Emulator, part 2
6 minute read
Published:
Last week, I set up the beginnings of a 6502 emulator, including the core codebase. Unfortunately, a command line application that just runs 6502 assembly code is super hard to debug. The 6502 isn’t equipped with any way to print output by default (unless you’d hook up a 65C22 VIA, but coding that seems tricky), and reading raw bytecode isn’t the easiest thing to do. Other emulators I’ve used (ex. Symon) include a pretty nice GUI to debug applications. I didn’t want to go as far as writing a whole application frontend, but I did think implementing some kind of updated UI would be a great addition for both users and for my personal debugging.
Writing a 6502 Emulator
8 minute read
Published:
I recently watched an awesome video from Computerphile about writing an emulator for the Atari 2600. The 2600 runs off a 6507 processor, which is basically a modified 6502. This got me thinking: how hard would it actually be to write an emulator for a 6502 computer? At this point I’ve already built a computer with one and am close to having a working Forth interpreter–so I’m pretty familiar with how the microprocessor works internally.