Francis Stokes
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francis.codes
Francis Stokes
@francis.codes
300 followers 490 following 130 posts
Exploring the Low Level on YouTube as Low Byte Productions

Firmware Engineer

Father x2

(he/him) 🇬🇧🇳🇱
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francis.codes
I've been experimenting with tenting, but I'm not sure if I'm all in. For long extended typing I think I prefer flat, but for regular coding work where it's not constant, the tenting feels really good
Overhear view of the keyboard with the white 3d printed tenting risers set apart.
October 4, 2025 at 7:45 AM
francis.codes
This is my 3rd mechanical keyboard design. I went for a full split this time. It's 3D printed, including the low profile key caps. The switches are gazzew silent black. The halves are wired direct, with 10 pin IDC connectors carrying the rows and columns. No PCB either, the matrix is hand-wired.
A 40% split mechanical keyboard. Both halves are black, symmetrical, with all black keys, except the F, J, and the two space bar keys which are white. None of the keys have symbols. The left half has an exposed raspberry Pi pico, where a USB C cable plugs in. The right half has a decorative feature where the pico would be. The two halves are connected with a decorative cable sheaved in patterned black and white paracord. Both sides are raised up on a small white platform to create an approximate 15° tenting angle.
October 4, 2025 at 7:41 AM
francis.codes
I've fallen down the rabbit hole of building keyboards lately. This is my take on a planck, with a pseudo-split.
Hand-wired with 48 keys, 4 RGB LEDs, runs QMK + Vial on a raspberry pi pico.
It only took me about a day to get used to it, which was a surprise considering it's my first ortholinear!
A view of the fully assembled keyboard on a wooden table. A coiled USB C cable plugs into an exposed raspberry pi pico board which is mounted to the top plate of the keyboard. On either side of the pico sits 24 keys - a distance of about 3cm apart. The keycap set is grayscale, with the bottom row of keys all being white, and the next 3 becoming progressively darker in value. Under the pico there are 4 WS2812 LEDs used for status. An in-progress view of the keyboard being built. The plate is shown upside down with all 48 keys pressed in. The keys are connected together in a hand-wired matrix, with the main backbone of the matrix being made of solid 1mm copper wire. The rows and columns are connected to exposed pins of the raspberry pi pico module with somewhat questionable soldering. The left side is done, while the right side is not yet complete. The RGB LEDs are not connected at all, and the leftmost one is missing entirely.
July 31, 2025 at 1:56 PM
francis.codes
Hexagonal fractal constructed by drawing a circle, with 6 circles inside, and each circle gets 6 more circles inside, etc
March 7, 2025 at 10:03 PM
francis.codes
A serpinsky triangle, constructed by recursively drawing a circle, with 3 circles inside with half the radius, with each circle getting 3 more, and so on.
March 7, 2025 at 9:56 PM
francis.codes
I've got some exciting news to share soon!
A custom built pen plotter, sitting on a (somewhat) messy wooden desk. There is a sharpie pen in the modular pen holder. It appears to be drawing an interrupted circle. To the left of the machine is an organised chaos of wiring harnesses, going off to a couple of hand soldered boards, with an STM32 nucleo devboard at the heart. To the right, tweezers, a crimp tool, and a partial laptop can be seen.
February 2, 2025 at 8:11 AM
francis.codes
If all goes well, I'll be streaming tomorrow afternoon (approximately 1400 UTC+1), reverse engineering the signalling on this remote control, and trying to turn it into a real USB keyboard
Two sides of a ziggo remote control. One side is a normal TV remote, and the other I a little keyboard, intended for use with a media center package
December 27, 2024 at 11:25 AM
francis.codes
A small but impactful hack for my setup at work:

A switch that maps my keyboard to either my Linux or Windows machine.

It's literally just a SP4T switch, a couple of sliced up USB cables, and a cap across the power supply.

The cap keeps remap settings when switching between computers.
Overhead shot of my mechanical keyboard on my desk. The micro USB end goes into a little black box, with a two position switch. Two USB-A wires come out of two sides of the black box, going off to different computers. A shot of the underside of the black box, where the electrical connections are shown. It's not what you'd call pretty! The USB cables are sliced up and soldered in place to the SP4T switch. A 100uF through hole capacitor is soldered across the power rails, with a piece of heat shrink protecting the ground leg from shorting other contact points.
December 20, 2024 at 8:16 AM
francis.codes
Tip for using a (non-cryptographic) pseudorandom number generator in an embedded context:

Define a .noinit section in RAM in the linkerscript with (NOLOAD), and then define an uninitialised array of u32s. Sum these up and use them to seed the RNG at boot time, when RAM will contain garbage.
#define ENTROPY_POOL_SIZE (32) __attribute__((section(".noinit"))) static u32 ram_entropy_pool[ENTROPY_POOL_SIZE]; static void init_xorshift(void) { u32 seed = 0; for (u32 i = 0; i < ENTROPY_POOL_SIZE; i++) { seed += ram_entropy_pool[i]; } xorshift32_seed(seed); for (u32 i = 0; i < ENTROPY_POOL_SIZE; i++) { ram_entropy_pool[i] = xorshift32_get(); } } .noinit (NOLOAD) : { *(.noinit*) } >ram . = ALIGN(4);
December 12, 2024 at 7:29 PM
francis.codes
I'm sorry, what!?!
A screenshot of my podcast feed, opened on the podcast "Roguelike Radio". It shows a new episode uploaded 18 hours again, with the last one before that being 4 years ago.
December 10, 2024 at 7:27 AM
francis.codes
I've seen copilot generate some unhinged code, but it just went comically off the rails here
typedef struct TCPConnection_t { ... QueueHandle_t rx_queue; QueueHandle_t tx_queue; SemaphoreHandle_t rx_lock; SemaphoreHandle_t tx_lock; SemaphoreHandle_t state_lock; SemaphoreHandle_t unacked_lock; SemaphoreHandle_t unprocessed_lock; SemaphoreHandle_t rx_queue_lock; SemaphoreHandle_t tx_queue_lock; SemaphoreHandle_t rx_queue_empty; SemaphoreHandle_t tx_queue_empty; SemaphoreHandle_t rx_queue_full; SemaphoreHandle_t tx_queue_full; SemaphoreHandle_t rx_queue_not_full; SemaphoreHandle_t tx_queue_not_full; SemaphoreHandle_t rx_queue_not_empty; SemaphoreHandle_t tx_queue_not_empty; SemaphoreHandle_t rx_queue_not_empty_and_not_full; SemaphoreHandle_t tx_queue_not_empty_and_not_full; SemaphoreHandle_t rx_queue_empty_and_not_full; SemaphoreHandle_t tx_queue_empty_and_not_full; SemaphoreHandle_t rx_queue_empty_and_not_empty; SemaphoreHandle_t tx_queue_empty_and_not_empty; SemaphoreHandle_t rx_queue_full_and_not_empty; SemaphoreHandle_t tx_queue_full_and_not_empty; SemaphoreHandle_t rx_queue_full_and_not_full; SemaphoreHandle_t tx_queue_full_and_not_full; SemaphoreHandle_t rx_queue_empty_and_not_full_and_not_empty; SemaphoreHandle_t tx_queue_empty_and_not_full_and_not_empty; SemaphoreHandle_t rx_queue_full_and_not_full_and_not_empty; SemaphoreHandle_t tx_queue_full_and_not_full_and_not_empty; SemaphoreHandle_t rx_queue_empty_and_not_full_and_not_empty_and_not_full; SemaphoreHandle_t tx_queue_empty_and_not_full_and_not_empty_and_not_full; SemaphoreHandle_t rx_queue_full_and_not_full_and_not_empty_and_not_full; SemaphoreHandle_t tx_queue_full_and_not_full_and_not_empty_and_not_full; SemaphoreHandle_t rx_queue_empty_and_not_full_and_not_empty_and_not_full_and_not_empty; SemaphoreHandle_t tx_queue_empty_and_not_full_and_not_empty_and_not_full_and_not_empty; SemaphoreHandle } TCPConnection_t;
December 4, 2024 at 1:20 PM
francis.codes
I got an IP address

My second post about building a networking stack on a microcontoller just dropped.

It covers the packet flow architecture in the firmware, the DHCP process, and a little debugging for flavour

github.com/francisrstok...
A block diagram showing the firmware and packet flow architecture. On the edge of the system there is a SPI/Ethernet connection. That is connected to a "net" block, which h contains a "w5100 driver" abstracted by a "generic ethernet driver". Received packets flow into a layer containing an IP module (and an unimplemented ARP module), from IP into UDP (as well as unimplemented TCP and ICMP modules), and from UDP to a queue on the DHCP module. Outgoing packets flow back up through the same layers.
November 27, 2024 at 7:13 AM
francis.codes
Wrote about a project I've been working on: github.com/francisrstok...
Close up (almost macro) shot of a a bodged arduino ethernet shield, plugged into an STM32 nucleo development board, plugged into a not-completely-discernible protoboard. There are wires of various kinds sprawling out of different parts of the stacked device, and 4 prominent, shining LEDs marked: PWR, LINK, 100M, and FULLD
November 9, 2024 at 9:03 PM
francis.codes
November 1, 2024 at 6:37 AM
francis.codes
It stuck me just how comical it is to have so many different types of connections between the same two devices
Laptop connected to a development board over USB, with a logic analyser attached to the board and connected to the laptop over USB, and an ethernet connection between the laptop and the board.
November 1, 2024 at 6:13 AM