Use control port for VIP (blending mixer / test pattern generator)

Hello.

I have a problem with using the control port for the test pattern generator and the alpha blending mixer.

I can write to the registers as defined in the VIP User Guide with IOWR/RD, but with no effect to my VGA screen.

I don't understand the pseudo code completely (page 152 from User Guide)

go = 0;
while (true)
{
status = 0;
while (go != 1 )
wait();
read_control();     //Copies control to internal register
status = 1;
do once for progressive output or twice for interlaced output
{
send_control_packet();
send_image_data_header();
output_test_pattern ();
}
}

especialy the last five lines. The other lines I do understand, that is setting / unsetting the registers, but the last five? Where do I get the data header from?

Can somebody explain it to me? Or has an link to some C source code?

P.S.

I have attached the test pattern generator directly to the vga controller (with timing adapter), with NIOS processor > uC/OSII.

Thank you