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+BogdanTheGeek's Blog
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+  • [6]About
+  • [7]Insights
+  • [8]Projects
+  • [9]Thoughts
+
+[10]Hosting a WebSite on a Disposable Vape
+
+2025-09-13Bogdan Ionescu6 min read (1266 words)[11]source [12]report issue
+#[13]programming  #[14]arm  #[15]tools  #[16]electronics  Hosting a WebSite on
+a Disposable Vape
+
+Preface[17]#
+
+This article is NOT served from a web server running on a disposable vape. If
+you want to see the real deal, click [18]here. The content is otherwise
+identical.
+
+Background[19]#
+
+For a couple of years now, I have been collecting disposable vapes from friends
+and family. Initially, I only salvaged the batteries for “future” projects
+(It’s not hoarding, I promise), but recently, disposable vapes have gotten more
+advanced. I wouldn’t want to be the lawyer who one day will have to argue how a
+device with USB C and a rechargeable battery can be classified as “disposable”.
+Thankfully, I don’t plan on pursuing law anytime soon.
+
+Last year, I was tearing apart some of these fancier pacifiers for adults when
+I noticed something that caught my eye, instead of the expected black blob of
+goo hiding some ASIC (Application Specific Integrated Circuit) I see a little
+integrated circuit inscribed “PUYA”. I don’t blame you if this name doesn’t
+excite you as much it does me, most people have never heard of them. They are
+most well known for their flash chips, but I first came across them after
+reading Jay Carlson’s blog post about [20]the cheapest flash microcontroller
+you can buy. They are quite capable little ARM Cortex-M0+ micros.
+
+Over the past year I have collected quite a few of these PY32 based vapes, all
+of them from different models of vape from the same manufacturer. It’s not my
+place to do free advertising for big tobacco, so I won’t mention the brand I
+got it from, but if anyone who worked on designing them reads this, thanks for
+labeling the debug pins!
+
+What are we working with[21]#
+
+The chip is marked PUYA C642F15, which wasn’t very helpful. I was pretty sure
+it was a PY32F002A, but after poking around with [22]pyOCD, I noticed that the
+flash was 24k and we have 3k of RAM. The extra flash meant that it was more
+likely a PY32F002B, which is actually a very different chip.^[23]1
+
+So here are the specs of a microcontroller so bad, it’s basically disposable:
+
+  • 24MHz Coretex M0+
+  • 24KiB of Flash Storage
+  • 3KiB of Static RAM
+  • a few peripherals, none of which we will use.
+
+You may look at those specs and think that it’s not much to work with. I don’t
+blame you, a 10y old phone can barely load google, and this is about 100x
+slower. I on the other hand see a blazingly fast web server.
+
+Getting online[24]#
+
+The idea of hosting a web server on a vape didn’t come to me instantly. In
+fact, I have been playing around with them for a while, but after writing my
+post on [25]semihosting, the penny dropped.
+
+If you don’t feel like reading that article, semihosting is basically syscalls
+for embedded ARM microcontrollers. You throw some values/pointers into some
+registers and call a breakpoint instruction. An attached debugger interprets
+the values in the registers and performs certain actions. Most people just use
+this to get some logs printed from the microcontroller, but they are actually
+bi-directional.
+
+If you are older than me, you might remember a time before Wi-Fi and Ethernet,
+the dark ages, when you had to use dial-up modems to get online. You might also
+know that the ghosts of those modems still linger all around us. Almost all USB
+serial devices actually emulate those modems: a 56k modem is just 57600 baud
+serial device. Data between some of these modems was transmitted using a
+protocol called SLIP (Serial Line Internet Protocol).^[26]2
+
+This may not come as a surprise, but Linux (and with some tweaking even macOS)
+supports SLIP. The slattach utility can make any /dev/tty* send and receive IP
+packets. All we have to do is put the data down the wire in the right format
+and provide a virtual tty. This is actually easier than you might imagine,
+pyOCD can forward all semihosting through a telnet port. Then, we use socat to
+link that port to a virtual tty:
+
+pyocd gdb -S -O semihost_console_type=telnet -T $(PORT) $(PYOCDFLAGS) &
+socat PTY,link=$(TTY),raw,echo=0 TCP:localhost:$(PORT),nodelay &
+sudo slattach -L -p slip -s 115200 $(TTY) &
+sudo ip addr add 192.168.190.1 peer 192.168.190.2/24 dev sl0
+sudo ip link set mtu 1500 up dev sl0
+
+Ok, so we have a “modem”, but that’s hardly a web server. To actually talk TCP/
+IP, we need an IP stack. There are many choices, but I went with [27]uIP
+because it’s pretty small, doesn’t require an RTOS, and it’s easy to port to
+other platforms. It also, helpfully, comes with a very minimal HTTP server
+example.
+
+After porting the SLIP code to use semihosting, I had a working web server&
+mldr;half of the time. As with most highly optimised libraries, uIP was
+designed for 8 and 16-bit machines, which rarely have memory alignment
+requirements. On ARM however, if you dereference a u16 *, you better hope that
+address is even, or you’ll get an exception. The uip_chksum assumed u16
+alignment, but the script that creates the filesystem didn’t. I actually
+decided to modify a bit the structure of the filesystem to make it a bit more
+portable. This was my first time working with perl and I have to say, it’s
+quite well suited to this kind of task.
+
+Blazingly fast[28]#
+
+So how fast is a web server running on a disposable microcontroller. Well,
+initially, not very fast. Pings took ~1.5s with 50% packet loss and a simple
+page took over 20s to load. That’s so bad, it’s actually funny, and I kind of
+wanted to leave it there.
+
+However, the problem was actually between the seat and the steering wheel the
+whole time. The first implementation read and wrote a single character at a
+time, which had a massive overhead associated with it. I previously benchmarked
+semihosting on this device, and I was getting ~20KiB/s, but uIP’s SLIP
+implementation was designed for very low memory devices, so it was serialising
+the data byte by byte. We have a whopping 3kiB of RAM to play with, so I added
+a ring buffer to cache reads from the host and feed them into the SLIP poll
+function. I also split writes in batches to allow for escaping.
+
+Now this is what I call blazingly fast! Pings now take 20ms, no packet loss and
+a full page loads in about 160ms. This was using almost all of the RAM, but I
+could also dial down the sizes of the buffer to have more than enough headroom
+to run other tasks. The project repo has everything set to a nice balance
+latency and RAM usage:
+
+Memory region         Used Size  Region Size  %age Used
+           FLASH:        5116 B        24 KB     20.82%
+             RAM:        1380 B         3 KB     44.92%
+
+For this blog however, I paid for none of the RAM, so I’ll use all of the RAM.
+
+As you may have noticed, we have just under 20kiB (80%) of storage space. That
+may not be enough to ship all of React, but as you can see, it’s more than
+enough to host this entire blog post. And this is not just a static page
+server, you can run any server-side code you want, if you know C that is.
+
+Just for fun, I added a json api endpoint to get the number of requests to the
+main page (since the last crash) and the unique ID of the microcontroller.
+
+Resources[29]#
+
+  • [30]Code for this project
+
+━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+ 1. While getting things together for this post, I came across [31]this project
+    that correctly identified these MCUs as PY32C642, which are pretty much
+    identical to the 002B. [32]↩︎
+
+ 2. Later modems used PPP (Point-to-Point Protocol) [33]↩︎
+
+© 2025 Bogdan Ionescu
+
+References:
+
+[1] https://bogdanthegeek.github.io/blog/
+[2] https://bogdanthegeek.github.io/blog/about
+[3] https://bogdanthegeek.github.io/blog/insights
+[4] https://bogdanthegeek.github.io/blog/projects
+[5] https://bogdanthegeek.github.io/blog/thoughts
+[6] https://bogdanthegeek.github.io/blog/about
+[7] https://bogdanthegeek.github.io/blog/insights
+[8] https://bogdanthegeek.github.io/blog/projects
+[9] https://bogdanthegeek.github.io/blog/thoughts
+[10] https://bogdanthegeek.github.io/blog/projects/vapeserver/
+[11] https://github.com/BogdanTheGeek/blog/tree/main/content/projects/vapeserver.md
+[12] https://github.com/BogdanTheGeek/blog/issues/new?template=corrections.md&title=[Correction]:%20Hosting%20a%20WebSite%20on%20a%20Disposable%20Vape
+[13] https://bogdanthegeek.github.io/blog/tags/programming/
+[14] https://bogdanthegeek.github.io/blog/tags/arm/
+[15] https://bogdanthegeek.github.io/blog/tags/tools/
+[16] https://bogdanthegeek.github.io/blog/tags/electronics/
+[17] https://bogdanthegeek.github.io/blog/projects/vapeserver/#preface
+[18] http://ewaste.fka.wtf/
+[19] https://bogdanthegeek.github.io/blog/projects/vapeserver/#background
+[20] https://jaycarlson.net/2023/02/04/the-cheapest-flash-microcontroller-you-can-buy-is-actually-an-arm-cortex-m0/
+[21] https://bogdanthegeek.github.io/blog/projects/vapeserver/#what-are-we-working-with
+[22] http://pyocd.io/
+[23] https://bogdanthegeek.github.io/blog/projects/vapeserver/#fn:1
+[24] https://bogdanthegeek.github.io/blog/projects/vapeserver/#getting-online
+[25] https://bogdanthegeek.github.io/blog/insights/jlink-rtt-for-the-masses/
+[26] https://bogdanthegeek.github.io/blog/projects/vapeserver/#fn:2
+[27] https://github.com/adamdunkels/uip/tree/uip-0-9
+[28] https://bogdanthegeek.github.io/blog/projects/vapeserver/#blazingly-fast
+[29] https://bogdanthegeek.github.io/blog/projects/vapeserver/#resources
+[30] https://github.com/BogdanTheGeek/semihost-ip
+[31] https://github.com/grahamwhaley/py32c642_vape
+[32] https://bogdanthegeek.github.io/blog/projects/vapeserver/#fnref:1
+[33] https://bogdanthegeek.github.io/blog/projects/vapeserver/#fnref:2