In RISC-V, interrupts play a crucial role in the system’s exception handling mechanism, allowing the processor to respond to external events and/or internal conditions. Interrupts are a type of asynchronous exception that can occur at any time during program execution. They typically require the processor to pause its current activity, handle the interrupt, and then resume normal operation. One group of interrupts in RISC-V is Machine-Level Interrupts, which can be divided into three important categories:

• External interrupts – triggered by external hardware devices, such as uart and I/O devices.
• Timer interrupts – triggered by the processor’s timer.
• Software interrupts – generated by software instructions.

The mstatus register in RISC-V is a crucial control and status register that manages interrupt handling, privilege levels, and processor state. As a Machine-level (M-mode) register in RISC-V, it plays a key role in CPU configuration.

One of the most important Control and Status Registers (CSR) for enabling interrupts is mie. The corresponding read/write register that holds information on pending interrupts is mip.

For example, to enable the machine timer interrupt, we need to set mstatus.MIE and mie.MTIE interrupt-enable bits. A triggered interrupt can be seen in the mip.MTIP, the interrupt-pending bit for machine timer interrupt.