//
// syscall.C
//
// Description:
//  Implements the SYSCALL instruction.
//
// Version:
//      $Id$
//
// Revision:
//      $Log$
//
// Author:
//  Brian J. Alliet
//

#include "includes.h"

// This only allows for a little less than 256K of 
// dynamically alloced memory (libarch limits us to
// 1MB of memory)
static long mips_brk = 768*1024; 

long mips_syscall(long nr, long a0, long a1, long a2) {
    //fprintf(stderr,"syscall: %ld: (%ld,%ld,%ld)\n",nr,a0,a1,a2);
    switch(nr) {
        case 1: /* SYS_exit */
            printf("Process exited with status: %ld\n",a0);
            exit(a0);
            return 0;
        case 6: { /* SYS_write */
            char buf[1024];

            if(a2 > (long) sizeof(buf)) a2 = sizeof(buf);

            for(long i=0;i < a2;i++)
                buf[i] = (char) dmem.mem.get(a1+i);

            if(a0 != 1 && a0 != 2) return -81 /* EBADFD */;
            return write(a0,buf,a2);
        }
        case 8: { /* SYS_fstat */
            if(a0 != 1 && a0 != 2) return -81 /* EBADFD */;
            for(int i=0;i<60;i++) dmem.mem.put(a1+i,0);
            dmem.mem.put(a1+4,0x32); // st_mode == S_IFCHR
            return 0;
        }
        case 19: /* SYS_getpagesize */
            return 4096;
        case 7: { /* SYS_sbrk */
            if(a0 < 0) return -12 /* ENOMEM */;
            if(a0 == 0) return mips_brk;
            long old_brk = mips_brk;    
            a0 = (a0 + 3) & ~3;
            if((unsigned long) mips_brk + a0 >= MEM_SIZE - STACK_SIZE) {
                fprintf(stderr,"WARNING: out of heap space\n");
                return -12 /* ENOMEM */;
            }
            mips_brk += a0;
            return old_brk;
        }
        case 38: /* SYS_memset */
            for(long i=0;i<a2;i++) dmem.mem.put(a0+i,a1);
            return a0;
        default:
            fprintf(stderr,"Unknown syscall: %ld\n",nr);
            return -88 /* ENOSYS */;
    }
}