Linux: Useful programs for embedded Linux systems

• Dropbear: SSH server and client let you get a remote console on the target device and Copy files to/from the target device.
• thttpd: Tiny/Turbo/Throttling HTTP server
• Boa Webserver
• lighthttpd Webserver
• TinyLogin

To be continued...

C Programming: Bit Masking

Bit Masking Table:

1     - > Bit 1
2     - > Bit 2
4     - > Bit 3
8     - > Bit 4
16   - > Bit 5
32   - > Bit 6
64   - > Bit 7
128 - > Bit 8

Example:

if(buffer[0] & 1 == 0) 

{

    // Frist bit is set to 0

}
else

{

   // First bit is set to 1

} 

if(buffer[0] & 64 == 0) 

{

    // Bit number 7 is set to 0

}

else

{

    // Bit number 7 is set to 1

}

Linux: Quick note, U-Boot and BusyBox Compiling

# Root File System
    mkfs.jffs2 -r root-fs/ -o myRootImage.jffs2 -e 128 -l -n

# U-Boot
    $make distclean

    $export PATH=/opt/arm-2007q1/bin/:$PATH

    $make at91sam9263ek_config

    $make CROSS_COMPILE=/opt/arm-2007q1/bin/arm-none-linux-gnueabi-

    $mkimage -A arm -O linux -C none -T kernel -a 20008000 -e 20008000 -n linux-2.6 -d arch/arm/boot/Image uImage

    $mkimage -A arm -O linux -C none -T kernel -a 20008000 -e 20008000 -n linux-2.6 -d arch/arm/boot/zImage uImage

# Busybox
    $make defconfig
   
    $make ARCH=arm CROSS_COMPILE=/opt/arm-2007q1/bin/arm-none-linux-gnueabi- CONFIG_STATIC=y CONFIG_PREFIX=/home/mohamed/busyboxfs install

Embedded: SPI Bitbanging

#define CLKLOW()       // Put SCLK GPIO to LOW

#define CLKHIGH()      // Put SCLK GPIO to HIGH

#define ASSERTCS()     // Put /CS GPIO to LOW

#define DEASSERTCS()   // Put /CS GPIO to HIGH

#define READMISO()     // MISO GPIO status?

#define MOSIHIGH()     // MOSI GPIO to HIGH

#define MOSILOW()      // MOSI GPIO to LOW

#define POWERON()      // VCC GPIO to HIGH

#define POWERDOWN      // VCC GPIO to LOW

#define SPISPPED       140

void spi_init()
{
    POWERON();
    CLKHIGH();
    DEASSERTCS();  
}

/////////////////////////////////////////////////////////////////////////////////////////////////

void spi_write_byte_SPIBitBang8BitsMode0(unsigned char byte)
{       
    unsigned char bit;
    ASSERTCS();
    for (bit = 0; bit < 8; bit++) {
        /* write MOSI on trailing edge of previous clock */
        if (byte & 0x80)
            MOSIHIGH();
        else
            MOSILOW();
        byte <<= 1;
 
        /* half a clock cycle before leading/rising edge */
        SPIDELAY(SPISPEED/2);
        CLKHIGH();
 
        /* half a clock cycle before trailing/falling edge */
        SPIDELAY(SPISPEED/2);
 
        /* read MISO on trailing edge */
        //byte |= READMISO();
        CLKLOW();
    } 

    DEASSERTCS();

}

/////////////////////////////////////////////////////////////////////////////////////////////////

void spi_write_byte(unsigned char byte)   /* Pseudo Code */

{

    TEMP = 100000000B;

    SS = 0;

    SCK = 1; 

   WHILE(TEMP)

       MOSI = (WRITE_BUFFER && TEMP);

       TEMP >> 1;

       SCK ^= 1;

   END WHILE

   SS = 1

}

/////////////////////////////////////////////////////////////////////////////////////////////////

unsigned char spi_read_byte()   /* Pseudo Code */

{

   SS = 0;

   SCK = 1;

   Count = 8;

   WHILE(count)

      READ_BUFFER | = MISO;

      READ_BUFFER << 1;

      Count--;

      SCK ^= 1;

   END WHILE

   SS = 1

}

////////////////////////

void spi_stop()

{

   POWERDOWN();

}

For more information on SPI, please visit this Wikipedia article

Linux: Mounting JFFS2 on an MTD RAM Device

$ modprobe jffs2

$ modprobe mtdblock

$ modprobe mtdram

$ dd if=jffs2.bin of=/dev/mtdblock0

$ mount -t jffs2 /dev/mtdblock0 /mnt/flash

And now to save changes we do:

$ dd if=/dev/mtdblock0 of=new-jffs2.bin.

Linux: Creating a JFFS2 Root File System

mkfs.jffs2 -r /mnt/flash -e 128 -b -o rootfs.jffs2

First we mount the ext2 file system image on a loopback device on an arbitrary mount point on our development workstation. Next we invoke the MTD utility mkfs.jffs2 to create the JFFS2 file system image. 

The -r flag tells mkfs.jffs2 where the root file system image is located. 

The -e instructs mkfs.jffs2 to build the image while assuming a 128KB block size. The default is 64KB. JFFS2 does not exhibit its most efficient behavior if the Flash device contains a different block size than the block size of the image. Finally, we display a long listing and discover that the resulting JFFS2 root file system image has been reduced in size by more than 60 percent. When you are working with limited Flash memory, this is a substantial reduction in precious Flash resource usage.

The -b flag is the -big-endian flag. This instructs the mkfs.jffs2 utility to create a JFFS2 Flash image suitable for use on a big-endian target. 

Finally we boot target using:

console=ttyS0,115200 rootfstype=jffs2 root=/dev/mtdblock2

Linux: Adding a new boot argument to the Kernel

static unsigned int my_super_new_boot_argument = 1;

is_my_super_new_boot_argumennt(char *str)
{
  get_option(&str, &my_super_new_boot_argument);
  return 1;
}

/* Handle parameter "my_super_new_boot_argument=" */
__setup("my_super_new_boot_argument=",     is_my_super_new_boot_argumennt);

if (my_super_new_boot_argument) 

{
   /* ... */
}