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#include <fbos/init.h>
#include <fbos/printk.h>
#include <fbos/mm.h>
#include <fbos/sched.h>
#include <fbos/dt.h>
unsigned long init_stack[4][THREAD_SIZE / sizeof(unsigned long)];
struct task_struct tasks[4] = {
[TASK_INIT] = { .stack = init_stack[0], .addr = nullptr, .entry_offset = 0, },
[TASK_FIZZ] = { .stack = init_stack[1], .addr = nullptr, .entry_offset = 0, },
[TASK_BUZZ] = { .stack = init_stack[2], .addr = nullptr, .entry_offset = 0, },
[TASK_FIZZBUZZ] = { .stack = init_stack[3], .addr = nullptr, .entry_offset = 0, },
};
int next_task;
// TODO: this feels really brittle
__kernel void switch_to(int task_id)
{
const char *ddr = (const char *)tasks[task_id].addr + tasks[task_id].entry_offset;
asm volatile("csrc sstatus, %[mask]" : : [mask] "r"(1 << 8));
asm volatile("mv ra, %0" : : "r"(ddr));
asm volatile("csrw sepc, ra");
asm volatile("sret");
}
/*
* This is the main entry point of the kernel after head.S is done. This
* function can (and will) assume that everything has been reset and that we can
* start the whole thing.
*/
__noreturn __kernel void start_kernel(void *dtb)
{
printk("Welcome to FizzBuzz OS!\n");
// Extract information from the DTB blob.
struct initrd_addr addr = find_dt_initrd_addr(dtb);
extract_initrd((unsigned char *)addr.start, addr.end - addr.start);
next_task = TASK_UNKNOWN;
// At this point everything has already been handled: setup the interrupt
// vector and enable the timer to start ticking and scheduling the three
// tasks at hand.
seconds_elapsed = 0;
setup_interrupts();
idle();
}
__noreturn __kernel void idle(void)
{
for (;;) {
if (next_task != TASK_UNKNOWN && next_task != TASK_INIT) {
switch_to(next_task);
}
asm volatile("wfi");
}
}
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