A detailed walkthrough of implementing the first userspace serial driver for the Helios microkernel OS, written in the Hare programming language. Covers the initramfs tarball format, ELF driver loader, capability-based driver manifest system, and the serial driver's event loop handling IRQs, read/write buffering, and IPC endpoint communication. Demonstrates how Helios isolates drivers in userspace with only the specific capabilities they declare, providing stronger security than monolithic kernels like Linux.
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