I am currently working on Super OSD - an on screen display project. http://code.google.com/p/super-osd has all the details.
At the moment I'm using a dsPIC MCU to do the job. This is a very powerful DSP (40 MIPS @ 80 MHz, three-register single-cycle operations and a MAC unit) and, importantly, it comes in a DIP package (because I'm using a breadboard to prototype it.) I'm really getting every last bit of performance out of it running the OSD - the chip has about 200ns or 10 cycles per pixel on the output stage so the code has to be very optimised in this part (for this reason it will always be written in assembly.)
Now I was considering using an FPGA for this because due to the parallel architecture of such a chip it is possible to have a simple logic program running the OSD. Things like drawing lines and algorithmic code would be handled by an MCU, but the actual output would be done with an FPGA. And some simple things like setting pixels or drawing horizontal and vertical lines I would like to integrate onto the FPGA, to improve speed.
I have some questions:
- Will it cost significantly more? The cheapest FPGA's I found were ~£5 each and the dsPIC is £3 each. So it will cost more, but by how much?
- The dsPIC fits in a SO28 package. I would not like to go bigger than SO28 or TQFP44. Most FPGA's I've seen come in BGA or TQFP>100 packages, which aren't an option at the moment, due to the shear size, and the difficulty of soldering them myself.
- How much current is used by an FPGA? The dsPIC solution currently consumes about 55mA +/- 10mA, which is okay at the moment. Would an FPGA consume more or less? Is it variable, or is it pretty much static, like the dsPIC?
- I need at least 12KB of graphics memory to store the OSD graphics. Do FPGA's have this kind of memory available on the chip or is this only available with external chips?