Unable to get a high output on a GPIO pin

Hello,
I want to glow an LED on the GPIO and have written a program to modify the
registers. I have managed to write to the physical addresses of the GPIO
port B, as seen in 2440addr.h, but the voltage values are not coming as
expected.
my control register rGPBCON = 0x5555;
pullup register rGPBPUL = 0xff;
data register rGPBDAT = 0xf0;

I have made all the pins as output and have switched on the pins
GPB0,1,2,3. But when I check with a multimeter on GPB0 and GPB1, GPB0 has a
voltage of about -2.1V (with COM conected to ground and the red terminal
connected to GPB0)and GPB1 has a voltage of -0.3 V.
What could I be doing wrong?

Okay, on further investigation, it seems that somehow, the ground pin and
the VCC 3.3V pin functions got interchanged. However, modifying registers
still doesn't do anything, whereas now setting the pin value using the
sysfs method is working.
I have attached my code 
Thanks!

hello,
how to access PORT WITH out driver??