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Jan Waclawek
10/25/05 10:28
Read: 855 times

#102931 - video, timing, speeds etc.
Responding to: Phillip M Gallo's previous message
Phillip M Gallo said:
The ongoing work is baseband NTSC, monochrome, 256x192, resulting in a square addressable pixel.

OK so let's calculate a bit - correct me if I am wrong.

With direct generation of video in mcu, the mcu is occupied during the active display. For NTSC, there are 525 scan lines per field, so assuming you double the lines (don't interlace), active field is 2*192/525 = cca 73% in the vertical scale; assuming square pixels it means 0.73*0.73=cca 53% of the whole frame (it also means some displayed border, but that was the standard of those fun-8-bitters anyway). Of course the blank/sync generation takes up some time, too, but I think, overally we some 1/3 of the raw performance is still left.

This time might be enough for most of the applications, as for the 1-clocker DS89C4x0 my "mini-benchmark" gives a cca 22x performance enhancement compared to 12MHz plain vanilla 8051, so after the video-cut it has still has the power equivalent of a 30MHz 6-clocker or so (the SiLabs gave me extra 4x, but that does not take into account the jump cache misses, so it's probably slightly less).

This is only the raw power consideration. When it comes to "response", the main restriction is that during the active line the mcu cannot do anything else. This means that a minimum "tick" for any timing is around 64us; assuming, that only the most necessary processing will be performed during the rather short horizontal blanking period; and most of the computing will remain for the vertical blanking period occuring in a 60Hz pace. This also imposes limits for UART reception, but that seems to be quite OK, as the character time for 115200 bauds (8N1) is 87us so 2 characters should not occur during one horizontal line.
However, I2C/SPI slave is more-less excluded even if it would have hardware support (this is valid also for the faster SiLabs or anything else).

As the horizontal scan duration is around 64us, the square pixel and the 73% active field and 256 horizontal pixels give me some 5.5MHz pixel clock, which approximately can be generated as 1/6 of the maximum 33MHz (rotation takes 1 cycle and bit move takes 2, so 3 cycles are left for byte fetch etc. per pixel).

As for color, it is not impossible to produce some 2-bit, 4-bit or even 8-bit output per pixel at the given rate assuming fast external memory. However, this comes at a cost - not only the memory itself, but also the handling of it takes more time - 2, 4, 8 times (although some algorithms might come out faster for the 8-bit version...), and also the addressing space of the '51 is "eaten up"... (from 6kB for the monochrome version up to 48kB for the 8-bit "full color" :-) ).

All in all, I think this is doable and might work quite well; although later we migh find out that a hardware video would be better. And, this is still NTSC (ok I think PAL is not substantially differen); but for VGA, the horizontal scan rate doubles so that would be one order of magnitude harder to achieve.. maybe with the SiLabs, with some considerations?

Jan Waclawek

List of 67 messages in thread
8051 8-bit computer      Jeff Corr      10/19/05 06:09      
   (or z80)      Jeff Corr      10/19/05 06:10      
   8051 computer      Craig Steiner      10/19/05 08:05      
      I never cringe on a "fun exercise" I do,      Erik Malund      10/19/05 08:21      
         awesome?      Jeff Corr      10/19/05 11:09      
            Computer      Craig Steiner      10/19/05 11:45      
               8051 Computer.      Arif Deshmukh      10/19/05 11:57      
               Minor corrections      Craig Steiner      10/19/05 20:31      
                  11MHz?      Jan Waclawek      10/20/05 00:59      
                     Not sure      Craig Steiner      10/20/05 08:07      
                        Congratulations      José Félix Díaz Ivorra      10/20/05 11:25      
                           Actually it's teh same        Craig Steiner      10/20/05 12:38      
                        11MHz      Phillip M Gallo      10/20/05 11:33      
                        Re: 8051 computer      Valentin Angelovski      10/20/05 18:37      
                           Just us      Craig Steiner      10/20/05 21:12      
                              Project Team      Sriharsha Vedurmudi      10/21/05 00:42      
                                 me tried      Oleg Sergeev      10/21/05 01:13      
                                    thoughts on project      Jeff Corr      10/21/05 02:28      
                                       What is a true multitasking controller?      Russell Bull      10/21/05 03:54      
                                          multitasking controller      Jan Waclawek      10/21/05 04:05      
                                             video      Oleg Sergeev      10/21/05 06:30      
                                             continued..      Jeff Corr      10/22/05 19:37      
                                          continued..      Jeff Corr      10/22/05 19:35      
                                             I don't think so      Craig Steiner      10/22/05 20:02      
                                                color display?      Jeff Corr      10/22/05 21:36      
                                                   Predko Video      Phillip M Gallo      10/22/05 23:17      
                                                      yes      Jeff Corr      10/23/05 13:38      
                                                      video, timing, speeds etc.      Jan Waclawek      10/25/05 10:28      
                                                         Video Timing.      Phillip M Gallo      10/25/05 14:36      
                                                            6.2MHz pixel clock?      Jan Waclawek      10/26/05 01:20      
                                                               Pixel Clock      Phillip M Gallo      10/26/05 11:39      
                                                                  pix clock      Phillip M Gallo      10/26/05 15:10      
                                                                  overclocking      Jan Waclawek      10/26/05 15:20      
                                                                     pad pixels      Phillip M Gallo      10/26/05 16:15      
                                                just a suggestion      Erik Malund      10/24/05 11:54      
                                                   Speed      Craig Steiner      10/24/05 13:22      
                                                      DS'4x0      Phillip M Gallo      10/24/05 17:26      
                                                      DIP / surface mount      Jeff Corr      10/24/05 19:32      
                                                         a 100MHz chip in a perf board? methinks      Erik Malund      10/25/05 06:33      
                                                Hardware multitasking      Sasha Jevtic      10/24/05 17:49      
                                                Multitasking redefined      Dan Henry      10/25/05 06:55      
                                             Misplaced self belief...      Donald Catto      10/24/05 03:01      
                                                Daunting?      Andy Neil      10/24/05 04:08      
                                                breadboarded      Jeff Corr      10/24/05 12:05      
                                                   TRS-80      Andy Neil      10/24/05 13:07      
                                                      TRS80?      Jan Waclawek      10/24/05 14:45      
                                                         in the beginning there was ..      Erik Malund      10/24/05 14:52      
                                                         TRS-80 Info      Phillip M Gallo      10/24/05 14:54      
                                                            Man those were the days.      Jon Ledbetter      10/24/05 15:22      
                                                               That fast?      Craig Steiner      10/24/05 16:00      
                                                                  More retroinfo      José Félix Díaz Ivorra      10/24/05 16:49      
                                                                  TRS-80 forward speed.      Phillip M Gallo      10/24/05 17:11      
                                                                  Like I said, It was a long time ago      Jon Ledbetter      10/25/05 07:48      
                                                               hrm      Jeff Corr      10/24/05 19:16      
                                                                  TRS80 model 1 speed...      Rob Vassar      10/24/05 19:47      
                                                         TRS80      Jan Waclawek      10/25/05 07:55      
                                                            You think?      Craig Steiner      10/25/05 08:38      
                                                               OK so both      Jan Waclawek      10/25/05 10:30      
                                                   No pictures yet      Craig Steiner      10/24/05 13:27      
                                                      Video Capture Card?      Jon Ledbetter      10/24/05 13:31      
                                                         Nope      Craig Steiner      10/24/05 13:47      
                                                      video output      Jeff Corr      10/24/05 19:27      
                                                Qui?      Rob Vassar      10/24/05 18:45      
                                                Multitasking      Grant Beattie      10/25/05 10:44      
                                                   Real Time and Multi Tasking      Ian Bell      10/25/05 15:47      
                                             Maybe whomever has "no idea what I'm tal      Erik Malund      10/24/05 11:51      
      It's probably at least fast enough ...      Richard Erlacher      11/11/05 00:04      

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