Handle PLIC Interrupt in gem5

HiFive Unmatched
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Greetings. I am using the freedom-e-sdk to compile bare-metal applications for the gem5 simulator (it closely models HiFive Unmatched). In the simulator there is a plic that produces an interrupt (int_num = 26). Looking at the examples it’s not clear to me how to setup an interrupt handler. Could someone provide me with some example code on how to do this ? Any help is greatly appreciated.

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Try the SiFive github page and search for ‘baremetal’ for examples.

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@odxa20 By interrupt id=26 you mean GPIO18? You can also see a complete example code of a PLIC handler in the start.s file of Demonstrating MTVEC

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Thank you very much for the replies. The MTVEC example looks quite helpful. I will try to use it as baseline and report back. Concerning the interrupt id. In the gem5 system I am working on there are no GPIOS. I am using that interrupt id to signal that a custom accelerator finished its computation

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@pds I just tested the MTVEC demonstration in gem5 and it worked! Is there a way to achieve the same functionality using the freedom-metal API to make the code more accessible to other people ?

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Thanks @odxa20 As @dconn suggests, there is a freedom-metal example at plic-interrupts.c

A nice general discussion is in the SiFive Interrupt Cookbook though when it comes to PLIC the discussion is a bit abstract.

I like to think about RISC-V interrupt procedural handling flow with the following picture. Peripherals shown are for the FE310 SoC but the diagram is general for all types of core.

riscv-interrupt-handling-path
riscv-interrupt-handling-path1280×720 38.9 KB

You might also find these forum conversations helpful:
What is PLIC interrupt source start and end in interrupt source mapping? and Use of external interrupt in vectored mode.

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Thank you for the example code and similar threads. I had already found the plic-interrupts.c file but was confused as it was using the metal_switch API. How could I do the same thing but for a general external plic interrupt ?

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A slightly more general PLIC example with the freedom metal API is in the plic-baremetal repo; a more extended version is in example-plic-baremetal-multicore.

I still prefer the simplicity, minimal latency, and memory overhead of assembly for interrupt handlers.

Note that clearing the external interrupt source is peripheral specific, in addition to the claim/complete process.