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hello everyone and welcome to my talk
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state of retrogaming and Emacs
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[Music]
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first of all a little bit about myself
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my name is neilman I'm 28 years old
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I work as a cyber security consultant
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msg systems and
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test other people's web applications and
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review the source code for security
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problems
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you can reach me by email I have my own
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self-hosted git repositories
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and I have a blog where you can
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occasionally find new posts by me on all
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kinds of things not just emix things
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so but the motivation about this one I
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found that Emacs is the ultimate
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procrastination machine and there are
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lots of fun demonstrations I'll go over
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a few of them
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for example someone made a thing to
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order sell it for himself online so it
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doesn't have to walk over to the shop
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there's plenty rc bots there's some game
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things
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there's an emulator for the z machine
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which you can use to play zorg
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and so I asked myself at this point can
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you actually emulate retro games at
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60fps and it looked around a bit
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and found some projects but none that
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were actually able to
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do it at 60fps so I set out to do my own
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one
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and looked out for a console that you
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can actually emulate at that speed
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using emax with its very very limited
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rendering
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[Music]
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and here's the project chip8.el it's
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pretty much finished
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it clocks into under 1000 sourced lines
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of code
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it supports the superchip 8 extensions
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it runs at full speed all games behave
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okay as far as I'm concerned and
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yeah I'm pretty happy with it it's very
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much the hell world of emulation
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and I might maybe do some other
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emulation projects in the future
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now for the section which is the longest
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bunch of fun facts about ship a dot el
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which I've learned
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during this project so
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what the hell is debate anyway first of
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all unlike many other emulation game
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things it's not a console but a vm
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it was designed for easy parting of home
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computer games
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it wasn't terribly successful and but
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there's still a small community of
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enthusiasts
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writing games for it and there are even
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a few demos
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this vm has system specs it has a very
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very simple 8-bit cpu with 16 registers
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and
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36 fixed size instructions you have a
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whole
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4 kilobyte of ram you have a stack with
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16 return addresses
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the resolution is 64 by 32 black white
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pixels
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rendering is done by drawing sprites
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these are drawn in excel mode meaning
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that if you
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draw a sprite and set a bit it just
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flips over from black to white or white
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to black
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first one you have a modern buzz that
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can just beep at one
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frequency and most unusually there's a
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hexadecimal keypad as input
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so the keys are basically zero to nine
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and a to f
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so how does this whole thing work it
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runs an unspecified speed
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you'll probably have to do some fine
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tune you find the speed you're happy
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with
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sound and delay timers exist they count
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down at 60fps down to zero
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this is done so that you can play a
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sound at some specific time
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the game itself is loaded with a fixed
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offset into ram the program account is
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set to exactly that offset
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and from there it enters the game loop
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where decodes and instruction executes
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it for the side effects and just
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loops and does this at infinitum
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[Music]
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so the game was the first thing where
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into problems the usual game approach is
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to
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do stuff figure out how long to eight
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wait for exactly that much and
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repeat this doesn't work well in imax at
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all because well
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user input basically and
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Emacs is designed to just do whatever it
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needs to do whenever you enter use input
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instead of
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doing things at one specific time if you
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try to do
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interruptable sleep well you get
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unpredictable behavior
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for example can be the timer doesn't run
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at all at next time because you've
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accidentally cancelled it
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if you do uninterruptable sleep it's
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freezes instead which isn't what you
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want either
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so I went for timers which forced me to
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do inversion of control
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meaning that I have to write code in the
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style where it's just call it
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time and this allows this input to
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happen and to
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for things to progress at roughly the
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speed I want to
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so there's the skydiver function which
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is called a 60fps
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and I have to be very careful to not do
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too much in it
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and say this function execute cpu cycles
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decrypt the sound delay registers and
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redraw
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the screen so to map this whole system
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to mx lisp
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I've used just integers and vectors
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which contain even more integers
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this is used for the ram registers
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return stack key state screen and so on
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and so forth basically
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what you would do if you were writing c
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all of this is stored in global
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variables I'm not using any
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lists at all and as a side effect
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there's no constant going on at all
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there are no extra objects created which
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would trigger
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garbage collection pulses this getting
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this red was rather tricky actually and
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there were some
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in garbage collection problems which I
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had to resolve over time
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so the coding instructions for this you
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have to know that all instructions are
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two bytes long
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and the arguments encoded inside them
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for example the jump to address
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instruction
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is encoded as one and three hex digits
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the type is extracted masking with f000
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and then shifting it by 12 bits mask
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means the hd
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performance binary end you can do the
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same with the argument basement with
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zero fff
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and no shift if you do this long enough
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you'll find common patterns for example
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addresses are always encoded like this
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using the last three nibbles in the code
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you'll find a big count which dispatches
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on the type and executes it for the side
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effects
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[Music]
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for testing I've initially just accused
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the rom until I fit ctrl g
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and then use the debug command to run
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the screen to a buffer
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later on I found tiny roms that just
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display a static
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test screen for example logo and looked
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whether it looked right
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I added instructions as needed and went
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through more and more and more roms and
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later I wrote in unit test suite as a
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safety net and this unit test suite it
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just
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sets up an empty emulator state executes
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some instructions and then looks whether
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the
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expected side effects have happened
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for debugging I usually use e-debug but
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this was super ineffective because well
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you don't really want to step through
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big cons doing side effects for every
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single cycle when it can take like 100
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cycles for things to happen
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therefore I've set up logging and
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whenever I locked something
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and couldn't figure out the error I
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compared my lock output with
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instrumented version of another emulator
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and if the locks diverge then I have
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figured out where the bug lies and could
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look deeper into it
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future project idea might be a chip 8
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debugger but I doubt I'll ever
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go into it for analysis I initially
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wrote a disassembler which is a very
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simple thing but super tedious
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especially if you wanted to add advanced
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functionality for example analysis or
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thinking of what part is data what had
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this code
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and I had this great idea for using the
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radari 2 framework
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and adding analysis and disassembly
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plug-in for it
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so I looked into this found okay here
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where you can write plugins in c
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but also in python so I wrote one in
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python and then the scout there's
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actually existing one in core which you
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have to enable explicitly by passing its
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argument so I've tried it and found it's
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not exactly as good as my own one so
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improved this one and submitted pull
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requests until it was at the same level
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[Music]
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rendering was the trickiest part of this
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whole thing because
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well I decided against using a library
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not like there would have been any
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usable library for this
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my usual approach of accelerating svg
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file was too expensive it just created
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too much garbage and took too long time
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I then tried creating mutating strings
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this was either either too expensive
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just like svgs or too complicated I
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tried changing svg tiles which created
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gaps between the lines
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then I tried to create an xpm file which
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was backed by a bull vector
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administrating this bull vector
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but the image caching effect made it
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just every nth frame to appear which
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wasn't good either then I had the idea
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to just use plain text
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and paint the individual characters with
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a different background color this
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this had perfect perfect performance
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there were many optimization attempts
0:08:18.479,0:08:21.840
until I got there and it was
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very very stressful I wasn't sure
0:08:21.840,0:08:26.160
whether I would ever get to accept the
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performance at all
0:08:26.160,0:08:30.319
for sound you only need to a single beep
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so technically it shouldn't be difficult
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to emulate it
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however doing this is hard because Emacs
0:08:33.519,0:08:37.200
officially only supports synchronous
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playback of sounds
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but there's also emax process which you
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can launch in asynchronous way
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so I looked into it and found that
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employee has a slave mode and mpv
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supports listing on the
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fifo for commands so I've created a pipe
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started a past mpv in loop mode and
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always send in pause and pause command
0:08:55.519,0:09:01.839
to the fifo and that way I could control
0:08:58.000,0:09:01.839
when to start beeping and stop beeping
0:09:02.640,0:09:07.200
so yeah that's it so far was a very
0:09:05.760,0:09:09.279
educational experience
0:09:07.200,0:09:10.320
I have tried out a bunch of games which
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were
0:09:10.320,0:09:14.320
well I almost say the worst ports of
0:09:12.640,0:09:15.839
classic games I've ever tried
0:09:14.320,0:09:18.320
it wasn't terribly fun to play them but
0:09:15.839,0:09:21.760
was fun to improve the emulator until
0:09:18.320,0:09:23.279
well things worked good enough
0:09:21.760,0:09:25.120
and I've learned a lot about how
0:09:23.279,0:09:27.760
computers work at this level
0:09:25.120,0:09:28.880
so maybe maybe I'll in the future make
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another emulator
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but uh I'm not sure whether anything
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more advanced like intel 8080 emulator
0:09:34.000,0:09:37.839
will actually run mix fast enough
0:09:36.560,0:09:39.200
but it's still an interesting idea
0:09:37.839,0:09:39.600
because then you could actually have an
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os
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inside Emacs and fulfill that one
0:09:41.680,0:09:45.440
specific meme
0:09:43.120,0:09:47.279
but if I try to do most serious stuff
0:09:45.440,0:09:48.000
I'll probably use chicken scheme which
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is my
0:09:48.000,0:09:53.279
preferred language for serious projects
0:09:49.920,0:09:57.839
and writing neso gamer emulator
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and that's it thank you
