[SOLVED] MIPS traps not working?

irvanherz · **Joined:** Mon Sep 19, 2016 5:34 am **Posts:** 27

Hello guys, I'm triying to develop simple hello world OS. But I get stuck in interrupt/traps handling. It seem that I miss something,
I have read MIPS32TM Architecture For Programmers Volume III: The MIPS32TM Privileged Resource Architecture. It was said that trap vector for software interrupt is 0x80000180. So, I made new section with VMA base address for interrupt handler at that address. But, why this code not working?

kernel.c

Code:

/* mipsel-linux-gnu-gcc -mips32 -EL -c kernel.c -o kernel.o */
/* mipsel-linux-gnu-ld -Tscript.txt interrupt.o start.o kernel.o -o kernel.elf */
/* qemu-system-mipsel -machine mips -nographic -kernel kernel.elf */

#define R4K_MMIO_BASE 0x14000000
#define R4K_UART0_BASE (R4K_MMIO_BASE + 0x3F8)

void init_uart0() {
    *((char*)(R4K_UART0_BASE + 1)) = 0;
    *((char*)(R4K_UART0_BASE + 3)) = 0x80;
    *((char*)(R4K_UART0_BASE + 0)) = 0x03;
    *((char*)(R4K_UART0_BASE + 1)) = 0x00;
    *((char*)(R4K_UART0_BASE + 3)) = 0x03;
    *((char*)(R4K_UART0_BASE + 2)) = 0xc7;
    *((char*)(R4K_UART0_BASE + 4)) = 0x0b;
}

void print_uart0(const char *s) {
   while(*s) {
      while((*((char*)(R4K_UART0_BASE + 5)) & 0x20) == 0); //wait
      *((char*)(R4K_UART0_BASE + 0)) = *s;
      s++;
   }
}
 
void KMain() {
   init_uart0();
   print_uart0("Hello world!\n");
   //Trap if 0
   asm("teqi $zero,0");
}

//Trap 0
void Int0() {
   print_uart0("Trap say hello world!\n");
}

interrupt.s

Code:

.text
   lui       $t1, %hi(Int0)
   addiu     $t1, %lo(Int0)
   jalr      $t1
   eret

start.s

Code:

/* mipsel-linux-gnu-gcc -mips32 -EL -c start.S -o start.o */

.global _start
_start:
   lui      $sp, %hi(STACK_TOP)
   addiu   $sp, $sp, %lo(STACK_TOP)

   # Enable interrupts in status register
   # bit 0 : Global interrupt enable flag
   # bit 8-15 : Interrupt mask. 1=enabled
   mfc0    $t0, $12
   ori    $t0, $t0, 0xFF01
   mtc0    $t0, $12
   
   lui     $t1, %hi(KMain)
   addiu   $t1, %lo(KMain)
   jalr    $t1
   j .

script.txt

Code:

ENTRY(_start)
SECTIONS
{
 . = 0x80000180;
 .interrupt : { interrupt.o(.text) }
 . = 0x80100400;
 .startup . : {start.o(.text) }
 .text : { *(.text) }
 .data : { *(.data) }
 .bss : { *(.bss COMMON) }
 . = ALIGN(8);
 . = . + 0x1000; /* 4kB of stack memory */
 STACK_TOP = .;
}

After I built and run it under qemu, "Hello world" shown up. But, nothing more. I can't see message from Int0().
Is there anything I missed?

dchapiesky · **Joined:** Sun Dec 25, 2016 1:54 am **Posts:** 204

Could you add a loop please...

Code:

void KMain() {
   init_uart0();
   print_uart0("Hello world!\n");
   //Trap if 0
   asm("teqi $zero,0");
   while(1) {}
}

I just wonder if qemu is exiting simulation before passing the interupt along to your handler....

irvanherz · **Joined:** Mon Sep 19, 2016 5:34 am **Posts:** 27

Quote:

I just wonder if qemu is exiting simulation before passing the interupt along to your handler....

Thanks for your answer. But, finally I found that interrupt still not well prepared. So, this code work well for me

Code:

/* mipsel-linux-gnu-gcc -mips32 -EL -c start.S -o start.o */
.global _start
_start:
   lui      $sp, %hi(STACK_TOP)
   addiu   $sp, $sp, %lo(STACK_TOP)

   # Enable interrupts in status register
   # bit 0 : Global interrupt enable flag
   # bit 8-15 : Interrupt mask. 1=enabled
   # bit 22 : location of interrupt vector. 0:boostrap, 1:normal
   # bit 29-32 : Coprocessor enabled flag
   mfc0    $t0, $12
   
   lui      $t1, 0xFFBF
   ori      $t1, 0xFFFF
   and      $t0, $t0, $t1
   
   lui      $t1, 0xF000
   ori    $t1, $t1, 0xFF07
   or       $t0, $t0, $t1
   mtc0    $t0, $12
   
   lui     $t1, %hi(KMain)
   addiu   $t1, %lo(KMain)
   jalr    $t1
   j .

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[SOLVED] MIPS traps not working?

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