[GitHub] [nuttx] masayuki2009 commented on pull request #8762: Support for Kernel build with vexriscv-smp.

["masayuki2009 (via GitHub)" <gi...@apache.org>]

masayuki2009 commented on PR #8762:
URL: https://github.com/apache/nuttx/pull/8762#issuecomment-1463213402

   >qemu for whatever reason allows/handles the access from S -> M mode, maybe @masayuki2009 can explain how that >actually works. I think there is something in the command line options that allows this.
   
   In qemu-rv implementation with BUILD_KERNEL, we call `up_mtimer_initialize()` before transiting to S-mode.
   In addition, I added `qemu_rv_exception_m.S` to handle `qemu_rv_mtimer_interrupt()` which sends an S-mode software interrupt. In `qemu_rv_ssoft_interupt(), it calls `nxsched_process_timer()` if g_stimer_pending is true.
   
   As you can see in the `qemu_rv_ssoft_interupt()`, it also needs to handle IPI (Inter-Processor Interrupt) for SMP which we assume to use ACLINT instead of CLINT. Because ACLINT can send IPI in S-mode directly.
   
   https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc 
   


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