i'm contemplating a minimalist, small, digital video recorder that writes to an SD card or other flash standard. no screen. only a stop and record button. audio, which would at best be mono, isn't really necessary. my source is composite video. i'd like the recorded resolution to be 720x480 @ 30fps. compression and cpu can be adapted to meet these specs. can someone sketch (in functional blocks) or share some pointers on what would be needed and/or what chips could be used?? much appreciated.
If you're into FPGA's here is a sketch to a solution. I've used Xilinx tools most so their tools is in the example. Just insert your favorite FPGA contender.
- Use the 32-bit soft-CPU Microblaze as the main controller. It controls the buttons, LED's, SD-Card. controls the compression- coprocessor (see below) . I dont' think it's a good idea to use the Microblaze for video-compression through a software solution it would sink it..
- Use SPI to talk to the SD-Card, use the standard SPI-controller for Microblaze or some open-source that connect yourself against the Microblaze.
- For compression there are several alternatives(It should probably sit as a Co-processor for good thoughput between CPU and Compression- block) 1) Use a already developed IP-core from Xilinx that are already shipped with the correct Bus-interface to match Microblaze. Just look at the IP-catalog on the web or ask them. 2 ) Get an open-source Compression-core and develop the bus- interface yourself to match Microblaze (i think there are Wizard for that) 3) Develop your own CompressionBlock and connect it as a Co- processor.
As for handling the A/D for incoming Video/Audio you can probably find a circuit that does just that. Just make sure that the output of your A/D matches the format of the input of your compression block. It may demand a RGB-to-YUV that you can write yourself or find on OpenCores for example..
This way all your digtal logic is implemented in ONE circuit which is great when building it later. At least in small volumes.
The development board you would need for this would need quite some logic for the Compression-parts but of course you could simulate the whole system first and then buy a matching board. Maybe you would need some SD-RAM / DDR-RAM for the Compression algorithms, and if so just be sure to buy a development board that includes some.
I would however be interesting to compare the above solution against a solution using several circuits (seperate CPU, Compression-chip) that interconnect by PCB. Development-time/price? Cost of building each product?
Another solution could be to find a System-On-A-Chip that includes all you need:
1) CPU main controller
2) MMC/SD-Controller
3) SD-RAM / DDR-RAM controller
4) Video-compression or at least DSP-instructions.
Maybe the new Atmel AVR32 could fit this descripion... well you need to google on that..
wow spartan3wiz! *thanks* for the detailed response. that was very helpful. i haven't done fpga work,so i'll have a look at the avr32. i really appreciate it.
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