| ??? 09/02/04 17:52 Read: times |
#76826 - RE: Revisiting video & emulation Responding to: ???'s previous message |
Maybe video needn't be decided to "strictly". Decide an interface. How would the central '51 processor write to video? With this flexibility, a single chip '51 video display (which would be a lot of fun and challenge) would be just as approp as a VGA approach. I agree that an 8052-driven video would be more fun and more of a challenge. If we can get an 8052 derivative to generate decent pixel graphics resolution (i.e. not just text) and preferably with color then I'd prefer the 8052-driven approach. Preferably I'd like to see 640x480 with at least 16 colors. In regards to how the central 8052 would write to video, I was thinking along the lines of establishing some kind of communication between the chip. Could be I2C, straight serial, maybe parallel or some number of bits less than 8 in parallel to reduce the number of I/O lines dedicated to video. When the central 8052 wants to write to video we'd define some commands so that, perhaps, drawing a line from (0,0) to (640,480) would be something like (1)(10)[000][000][640][480] where the "1" is a single-byte command of "draw line", the "10" is a single-byte color code, and each of the bracketed numbers are 2-byte coordinates. So a line drawn from (0,0) to (640,480) would be sent to the dedicated 8052 video chip in 10 bytes. Additional commands could be defined to draw individual pixels, rectangles, squares, or whatever. Once the central 8052 writes the command out it can forget about it and leave the video 8052 in charge of updating its memory to reflect the new image. Now if the need for a single approach was desired perhaps a decision regarding two issues would help: 1) Target monitor (TV or VGA) 2) Color/Mono.
In a way the question is do you retain the "Atari" or adopt a "PC" metaphor. I think I'd personally prefer VGA output since we could just attach it to any old monitor we have around or connect it to a mini-VGA if we wanted to make a small portable unit (like the in-car GPS system I was talking about). VGA would also give us crisper graphics, presumably. This could be done with a single '51 variant but keep in mind that done this way you have no more screen display than you have integrated RAM. Why build a character display when bit mapping extends the functionality of even the lowest of resolution displays? I agree. Whether we do this B&W or color, TV or VGA, dedicated 8052 or external VGA chipset, I definitely think we should have pixel-level control of the display. If we just wanted text-based we might as well use an LCD. I believe Prahlad said we could do color VGA qualiy with 20-30 MIPS on an 8052. Can anyone else comment on whether this sounds right? If so, we could use a SiLabs part for the video. They have 128k RAM on-chip, I believe, so 640x480x4 colors would be possible with the on-chip RAM. Would additional XRAM off-chip of the SiLabs be too slow to use for additional video memory to try to get that up to 8 or 16 colors? Regards, Craig Steiner |
