Delayed Interrupt

Open Qsys and go to Nios properties.

Add a tightly coupled (TC) code port and possibly a TC data port.

Close Nios properties.

Add 2 onchip memories and connect one of them to Nios TC code port and the other to TC data port.

In your case I believe 4kByte for TC code memory is enough.

TC data must be large enough to store ImgBuff, then size >= (460 x 640 x 4) if you need 32bit data; this would be more than 1MByte and probably exceeds your fpga resources, so you can not use TC data and you have to keep data in ddr2.

Now, let's say you named tc_code your TC memory component.

Then place the following directive just after the declaration of a function you want to be executed in TC memory:

int main(void) __attribute__ ((section (".tc_code")));

The same can be done with variable you want to be accessed very very fast:

int fastBuffer[256] __attribute__ ((section (".tc_data")));