Going realmode in kernel drivers?

From: Peter B (pb_at_ludd.luth.se)
Date: 11/24/03

  • Next message: Eduard Martinescu: "[Fwd: TWE driver IOCTL's]" 
    To: freebsd-hackers@freebsd.org
Date: Mon, 24 Nov 2003 16:18:14 +0100 (MET)

    i386/FreeBSD-4.x/lkm.

    How does one get into 'realmode' inside a kernel driver?

    The reason for the need is a tight timeing loop that measures the lenght of
    pulses. And disableing interrupts is just not enough.
    Target cpu's are AMD K5 + AMD XP.

    Asfair when reading cycles per opcode. The number of cycles required increase
    about three times when useing protected mode or similar.

    Code excerpt:
        u_int32_t register cnt1;
        u_int32_t register cnt_max=0xFF;
        u_int32_t register *store_ptr;
        u_int32_t register *store_end;
        u_int8_t register last_val=0;

        store_ptr = ..;
        store_end = ..+ SIZ;

        disable_intr();
        for(;;)
            {
            for(cnt1=0; cnt1<cnt_max && ((inb(0x379)&0x20) != last_val); cnt1++)
                ;
            *(store_ptr++) = cnt1;
            if( store_ptr>=store_end )
                break;
            last_val ^= 0x20;
            }
        enable_intr();

    (Will start on a new count every signal flank).

       /P

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  • Next message: Eduard Martinescu: "[Fwd: TWE driver IOCTL's]"