If you settled for 320 x 480 the prop can fit a 1 bpp vga buffer into memory. You may be able to use external ram to if you over clock the chip to 100Mhz.
While working with AVR MCUs I have used 10ns SRAM wired so the data bus drives the input of an 74HCT244, which is disabled output durring blanking, and the AVR drives the SRAM address bus, during the blanking periods the AVR would write to this external frame buffer, this worked well for up to 12BPP@512x480 (using 640x480 Syncs) (the AVR did have to generate the Sync signals). with this in mind and the nature of the counters in the Prop I would think that the same could be done with the aid of the video generator to produce resolutions up to 1280x1024@12BPP having no palette limit (I am actually testing this very simple circuit this evening).
Oh yeah, the output of the 74hct244 is attached to the resistor DACs going to RGB.
While working with AVR MCUs I have used 10ns SRAM wired so the data bus drives the input of an 74HCT244, which is disabled output durring blanking, and the AVR drives the SRAM address bus, during the blanking periods the AVR would write to this external frame buffer, this worked well for up to 12BPP@512x480 (using 640x480 Syncs) ....
What did you find to be the limiting factor in your AVR project (as far as resolution) -- was it the AVR's MIPs limit, or some other h/w bottleneck? What type of buffer "rewrite" rate did you see? For my part, a buffer refresh rate north of 15-16Hz would be just fine, as long as I can keep the monitor cycling up in the 60+ range to eliminate flicker. (Granted, that's probably not the case with a majority of users/designers looking to squeeze full-blown VGA performance out of an MCU)
On the AVR it was the 20MIPs limit. On the Prop last night I got 1024x768@12BPP in a single cog with the aid of the video shifter.
Because the blanking time is significant on 640x480, you could easily get 20 frames per second on the prop if you redraw the entire buffer, if you only redraw those areas that change you can do much faster.
If you settled for 320 x 480 the prop can fit a 1 bpp vga buffer into memory. You may be able to use external ram to if you over clock the chip to 100Mhz.
FPGA is easier.
Kye/Leon - do you have an recommendations on an FPGA (and o/s programmer?) Since I live in the boonies and have to put in a parts order anyway, I might as well cover all bases. Thanks.
It only has 8-bit VGA, but using it will give you enough experience for building a better VGA system from an FPGA chip, RAM and a video DAC. VGA code is available for it.
I've got their Spartan 3 starter kit, which has eight-colour VGA capability. They also have VGA code for that that I've just downloaded, it gives both 640x480 and 800x600 resolutions. I'll give it a try.
Comments
FPGA is easier.
Oh yeah, the output of the 74hct244 is attached to the resistor DACs going to RGB.
What did you find to be the limiting factor in your AVR project (as far as resolution) -- was it the AVR's MIPs limit, or some other h/w bottleneck? What type of buffer "rewrite" rate did you see? For my part, a buffer refresh rate north of 15-16Hz would be just fine, as long as I can keep the monitor cycling up in the 60+ range to eliminate flicker. (Granted, that's probably not the case with a majority of users/designers looking to squeeze full-blown VGA performance out of an MCU)
Because the blanking time is significant on 640x480, you could easily get 20 frames per second on the prop if you redraw the entire buffer, if you only redraw those areas that change you can do much faster.
Kye/Leon - do you have an recommendations on an FPGA (and o/s programmer?) Since I live in the boonies and have to put in a parts order anyway, I might as well cover all bases. Thanks.
http://www.digilentinc.com/Products/Detail.cfm?NavPath=2,400,790&Prod=BASYS2
It only has 8-bit VGA, but using it will give you enough experience for building a better VGA system from an FPGA chip, RAM and a video DAC. VGA code is available for it.
I've got their Spartan 3 starter kit, which has eight-colour VGA capability. They also have VGA code for that that I've just downloaded, it gives both 640x480 and 800x600 resolutions. I'll give it a try.
Thank you, I'll take a look. With downloadable images how hard could it be??? (famous last words...)