Advent of Code is an Advent calendar of small programming puzzles for a variety of skill sets and skill levels that can be solved in any programming language you like.

The Conway’s Game of Life community celebrated a landmark achievement on November 9th, 2022. An idea years in the making, the “Reverse Caber Tosser” design finally had all of the pieces it needed to achieve its stated goal.

That goal is simple. Select any pattern that can be built in Life – for example, the Waterbear. Begin with a small number of gliders (now 15) in an otherwise empty Game of Life universe. After enough time goes by, those gliders need to build that pattern. No extra leftover debris, no stray scaffolding, just a pure synthesis of whatever you chose.

Normally, the GPU driver is responsible for details such as scheduling and prioritizing work on the GPU, and preempting jobs when they take too long to run to allow apps to use the GPU fairly. Sometimes the driver takes care of power management, and sometimes that is done by dedicated firmware running on a power management coprocessor. And sometimes there is other firmware taking care of some details of command processing, but it’s mostly invisible to the kernel driver. In the end, especially for simpler “mobile-style” GPUs like ARM Mali, the actual hardware interface for getting the GPU to render something is usually pretty simple: There’s the MMU, which works like a standard CPU MMU or IOMMU, and then the command processor usually takes pointers to userspace command buffers directly, in some kind of registers or ring buffer. So the kernel driver doesn’t really need to do much other than manage the memory and schedule work on the GPU, and the Linux kernel DRM (Direct Rendering Manager) subsystem already provides a ton of helpers to make writing drivers easy! There are some tricky bits like preemption, but those are not critical to get the GPU working in a brand new driver. But the M1 GPU is different…

Just like other parts of the M1 chip, the GPU has a coprocessor called an “ASC” that runs Apple firmware and manages the GPU. This coprocessor is a full ARM64 CPU running an Apple-proprietary real-time OS called RTKit… and it is in charge of everything! It handles power management, command scheduling and preemption, fault recovery, and even performance counters, statistics, and things like temperature measurement! In fact, the macOS kernel driver doesn’t communicate with the GPU hardware at all. All communication with the GPU happens via the firmware, using data structures in shared memory to tell it what to do. And there are a lot of those structures…

this repo will get suuuuuuper unsuablely bloated very soonthis repo will get suuuuuuper unsuablely bloated very soon