Herein are solutions for computer bus transaction processing by a device that is rebooting. Data and logic of a bus driver of a device are configured to remain loaded and fully operational during an operating system (OS) kernel reboot on the device. That logic is specially memory mapped into an unused area of volatile memory that is not overwritten by the OS kernel. Driver logic is self-contained such that its statically linked codebase contains all logic needed to detect and fully handle an outstanding bus transaction. In an embodiment having a host computer that is connected to a device by a bus, a central processing unit (CPU) of the device bootstraps an OS kernel of the device. Concurrent to bootstrapping the OS kernel, the CPU of the device detects a transaction on the bus that was not initiated by the device, executes an instruction sequence for the transaction, and sends on the bus a response to the transaction.