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kernel.c
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kernel.c
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#include <stddef.h>
#include "versatilepb.h"
#include "asm.h"
void *memcpy(void *dest, const void *src, size_t n) {
char *d = dest;
const char *s = src;
size_t i;
for(i = 0; i < n; i++) {
d[i] = s[i];
}
return d;
}
void bwputs(char *s) {
while(*s) {
while(*(UART0 + UARTFR) & UARTFR_TXFF);
*UART0 = *s;
s++;
}
}
void task(void) {
bwputs("In other task\n");
while(1);
}
#define STACK_SIZE 1024 /* Size of task stacks in words */
#define TASK_LIMIT 2 /* Max number of tasks we can handle */
#define PIPE_BUF 512 /* Size of largest atomic pipe message */
#define PIPE_LIMIT (TASK_LIMIT*5)
#define TASK_READY 0
#define TASK_WAIT_READ 1
#define TASK_WAIT_WRITE 2
void first(void) {
bwputs("In user mode 1\n");
if(!fork()) task();
bwputs("In user mode 2\n");
while(1);
}
struct pipe_ringbuffer {
int start;
int end;
char data[PIPE_BUF];
};
#define RB_PUSH(rb, size, v) do { \
(rb).data[(rb).end] = (v); \
(rb).end++; \
if((rb).end > size) (rb).end = 0; \
} while(0)
#define RB_POP(rb, size, v) do { \
(v) = (rb).data[(rb).start]; \
(rb).start++; \
if((rb).start > size) (rb).start = 0; \
} while(0)
#define RB_LEN(rb, size) (((rb).end - (rb).start) + \
(((rb).end < (rb).start) ? size : 0))
#define PIPE_PUSH(pipe, v) RB_PUSH((pipe), PIPE_BUF, (v))
#define PIPE_POP(pipe, v) RB_POP((pipe), PIPE_BUF, (v))
#define PIPE_LEN(pipe) (RB_LEN((pipe), PIPE_BUF))
unsigned int *init_task(unsigned int *stack, void (*start)(void)) {
stack += STACK_SIZE - 16; /* End of stack, minus what we're about to push */
stack[0] = 0x10; /* User mode, interrupts on */
stack[1] = (unsigned int)start;
return stack;
}
void _read(unsigned int *task, unsigned int **tasks, size_t task_count, struct pipe_ringbuffer *pipes);
void _write(unsigned int *task, unsigned int **tasks, size_t task_count, struct pipe_ringbuffer *pipes);
void _read(unsigned int *task, unsigned int **tasks, size_t task_count, struct pipe_ringbuffer *pipes) {
task[-1] = TASK_READY;
/* If the fd is invalid, or trying to read too much */
if(task[2+0] > PIPE_LIMIT || task[2+2] > PIPE_BUF) {
task[2+0] = -1;
} else {
struct pipe_ringbuffer *pipe = &pipes[task[2+0]];
if((size_t)PIPE_LEN(*pipe) < task[2+2]) {
/* Trying to read more than there is: block */
task[-1] = TASK_WAIT_READ;
} else {
size_t i;
char *buf = (char*)task[2+1];
/* Copy data into buf */
for(i = 0; i < task[2+2]; i++) {
PIPE_POP(*pipe,buf[i]);
}
/* Unblock any waiting writes
XXX: nondeterministic unblock order
*/
for(i = 0; i < task_count; i++) {
if(tasks[i][-1] == TASK_WAIT_WRITE) {
_write(tasks[i], tasks, task_count, pipes);
}
}
}
}
}
void _write(unsigned int *task, unsigned int **tasks, size_t task_count, struct pipe_ringbuffer *pipes) {
/* If the fd is invalid or the write would be non-atomic */
if(task[2+0] > PIPE_LIMIT || task[2+2] > PIPE_BUF) {
task[2+0] = -1;
} else {
struct pipe_ringbuffer *pipe = &pipes[task[2+0]];
if((size_t)PIPE_BUF - PIPE_LEN(*pipe) <
task[2+2]) {
/* Trying to write more than we have space for: block */
task[-1] = TASK_WAIT_WRITE;
} else {
size_t i;
const char *buf = (const char*)task[2+1];
/* Copy data into pipe */
for(i = 0; i < task[2+2]; i++) {
PIPE_PUSH(*pipe,buf[i]);
}
/* Unblock any waiting reads
XXX: nondeterministic unblock order
*/
for(i = 0; i < task_count; i++) {
if(tasks[i][-1] == TASK_WAIT_READ) {
_read(tasks[i], tasks, task_count, pipes);
}
}
}
}
}
int main(void) {
unsigned int stacks[TASK_LIMIT][STACK_SIZE];
unsigned int *tasks[TASK_LIMIT];
struct pipe_ringbuffer pipes[PIPE_LIMIT];
size_t task_count = 0;
size_t current_task = 0;
size_t i;
*(PIC + VIC_INTENABLE) = PIC_TIMER01;
*TIMER0 = 1000000;
*(TIMER0 + TIMER_CONTROL) = TIMER_EN | TIMER_PERIODIC
| TIMER_32BIT | TIMER_INTEN;
tasks[task_count] = init_task(stacks[task_count], &first);
task_count++;
/* Initialize all pipes */
for(i = 0; i < PIPE_LIMIT; i++) {
pipes[i].start = pipes[i].end = 0;
}
while(1) {
tasks[current_task] = activate(tasks[current_task]);
tasks[current_task][-1] = TASK_READY;
switch(tasks[current_task][2+7]) {
case 0x1: /* fork */
if(task_count == TASK_LIMIT) {
/* Cannot create a new task, return error */
tasks[current_task][2+0] = -1;
} else {
/* Compute how much of the stack is used */
size_t used = stacks[current_task] + STACK_SIZE
- tasks[current_task];
/* New stack is END - used */
tasks[task_count] = stacks[task_count] + STACK_SIZE - used;
/* Copy only the used part of the stack */
memcpy(tasks[task_count], tasks[current_task],
used*sizeof(*tasks[current_task]));
/* Set return values in each process */
tasks[current_task][2+0] = task_count;
tasks[task_count][2+0] = 0;
/* There is now one more task */
task_count++;
}
break;
case 0x2: /* getpid */
tasks[current_task][2+0] = current_task;
break;
case 0x3: /* write */
_write(tasks[current_task], tasks, task_count, pipes);
break;
case 0x4: /* read */
_read(tasks[current_task], tasks, task_count, pipes);
break;
case -4: /* Timer 0 or 1 went off */
if(*(TIMER0 + TIMER_MIS)) { /* Timer0 went off */
*(TIMER0 + TIMER_INTCLR) = 1; /* Clear interrupt */
}
}
/* Select next TASK_READY task */
while(TASK_READY != tasks[current_task =
(current_task+1 >= task_count ? 0 : current_task+1)][-1]);
}
return 0;
}