Cepu (short for cerebral processing unit) is an AArch64 system emulator. It boots Linux 7.1 to a BusyBox shell in about 3 seconds on my MacBook using a device tree and initramfs. It includes a custom accelerator device (CepuCel) and an out-of-tree Rust kernel driver that lets the emulator run simple CNN models.
- Architecture: Single-core AArch64 system emulator targeting an ARMv9-A subset, EL0/EL1 only, little-endian
- CPU: 200+ instruction encodings covering integer, SIMD/FP, load/store, branch, and system operations. 4-level MMU with 4KB pages.
- Devices: GICv2 interrupt controller, PL011 UART, ARMv8 generic timer (24 MHz)
- Accelerator: CepuCel, an MMIO device with ring-buffer command queue, runs matrix multiplication on a dedicated thread
- Disk: CepuDisk, an MMIO block device backed by a host file (
disk.img) — the guest can mkfs and mount it for storage that survives reboots - Drivers: Out-of-tree Linux kernel modules written in Rust (CepuCel accelerator, CepuDisk block driver on the Rust block-layer bindings)
See docs/running.md for how to build the kernel, initramfs, and device tree, and boot the emulator.
- Single core only, no SMP
- No EL2 (hypervisor) or EL3 (secure monitor)
- No GPU or display, headless with serial console
- CepuCel accelerator supports F32 matrix multiplication only
- Not cycle-accurate
I built Cepu to teach myself how CPUs work. You can read about the process at oguza.com/bits-all-the-way-down.
Licensed under the MIT license. See LICENSE.