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57 lines
1.9 KiB
57 lines
1.9 KiB
/*
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* Utility functions for process management.
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*
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* Note: in Lab1, only one process (i.e., our user application) exists. Therefore,
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* PKE OS at this stage will set "current" to the loaded user application, and also
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* switch to the old "current" process after trap handling.
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*/
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#include "riscv.h"
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#include "strap.h"
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#include "config.h"
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#include "process.h"
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#include "elf.h"
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#include "string.h"
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#include "spike_interface/spike_utils.h"
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//Two functions defined in kernel/usertrap.S
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extern char smode_trap_vector[];
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extern void return_to_user(trapframe*);
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// current points to the currently running user-mode application.
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process* current = NULL;
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//
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// switch to a user-mode process
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//
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void switch_to(process* proc) {
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assert(proc);
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current = proc;
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// write the smode_trap_vector (64-bit func. address) defined in kernel/strap_vector.S
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// to the stvec privilege register, such that trap handler pointed by smode_trap_vector
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// will be triggered when an interrupt occurs in S mode.
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write_csr(stvec, (uint64)smode_trap_vector);
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// set up trapframe values (in process structure) that smode_trap_vector will need when
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// the process next re-enters the kernel.
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proc->trapframe->kernel_sp = proc->kstack; // process's kernel stack
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proc->trapframe->kernel_trap = (uint64)smode_trap_handler;
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// SSTATUS_SPP and SSTATUS_SPIE are defined in kernel/riscv.h
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// set S Previous Privilege mode (the SSTATUS_SPP bit in sstatus register) to User mode.
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unsigned long x = read_csr(sstatus);
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x &= ~SSTATUS_SPP; // clear SPP to 0 for user mode
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x |= SSTATUS_SPIE; // enable interrupts in user mode
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// write x back to 'sstatus' register to enable interrupts, and sret destination mode.
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write_csr(sstatus, x);
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// set S Exception Program Counter (sepc register) to the elf entry pc.
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write_csr(sepc, proc->trapframe->epc);
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// return_to_user() is defined in kernel/strap_vector.S. switch to user mode with sret.
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return_to_user(proc->trapframe);
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}
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