MiniMig NTSC

[yaqube]

Hello guys!

I am working on an ECS implementation. I've decided to release intermediate version of the firmware which allows to switch between PAL and NTSC screen modes (or rather PAL-60Hz since there is no short/long line toggling and CPU bus runs at PAL frequency). This is done by a jumper which was used to switch between 15kHz and 31kHz mode.

The video output is only VGA compatible but I've implemented vertical and horizontal interpolation to make the display less blocky (you can independently enable each interpolation by putting a jumper over appropriate pins of the user i/o header - the details are in the picture attached with the firmware file). This is a temporary solution and in the final release it will be done by OSD menu. (PIC firmware upgrade will be necessary.)

If you can test some NTSC versions of games please do this and tell me if they work correctly or not.
Please also share your opinion how you like the interpolated display.

You can download the new firmware from:
http://www.mediafire.com/?mywzlxynsl1

Have fun!

[yaqube]

@alexh

Regarding the changes:
I have rewritten beam counters to use 28 MHz clock. I have implemented comparators to generate programmable sync and blanking as well as programmable screen size. The NTSC/PAL switch is a change of VTOTAL value in a vertical beam comparator. It is not strictly an NTSC mode since the long/short lines toggle is missing, the bus is run at PAL frequency (7.09 MHz) and the Agnus ID is not changed.

In the released version there might be actually some problems on different MiniMigs. The new beamcounters weren't properly synchronised to the bus clock. Additionally my MiniMigs use 10ns memory chips so I might not be aware of problems which some other people can encounter.

Unfortunately I don't have the source code of the released version since it was a work in progress. I have almost finished the implementation of the full ECS chipset. I will release it soon with all the sources.

It would be nice if in the meantime somebody else could implement writing to the emulated floppy drive.

  :-D

[yaqube]

I'm still working on the ECS. It's almost done but there are some things to do yet (i.e. full super hires support in Denise).

I decided to try to find the reasons why some games don't work. I've already found some incompatibilities and fixed them (i.e. NZ Story scrolls fine now) but there are still some. I have an almost fully working Action Replay and some debugging stuff build into my MiniMig. I hope it will help to hunt bugs quickly. If you can report which game and in what way does not work it will be very helpful.

I'm quite busy now but expect new firmware with sourcecode in a few weeks.

@alehx: Are you working on adf write support?

[yaqube]

boing4000 wrote:
@yaqube
What changes did you make for the 50/60Hz switching?
It acts like a PAL and NTSC machine, but some games and demos/intros then show different graphics effects.

The 50/60 Hz mode switch is very simple. The total number of lines in NTSC is limited from 312 (typical value for PAL) to 262. Every line is still 227 colour clocks long like in PAL and there is no short/long line toggling. So it isn't 100% NTSC compatible.
It was a very quick fix for people with monitors which can't sync down to 50Hz.
Many games/demos won't work correctly in NTSC mode because they've never been meant to.

This video filter idea is impressive, looks like a bilinear filter, very useful für large TFT screen
how is it made? please tell us :-)

Yes, it is actually bilinear filtering. I've always wanted my real Amiga to have interpolation of the low-res screens and I planned to build a flicker-fixer with this feature. Thanks to Dennis I could implement this on Minimig.

Now I'm working on improving compatibility with games which were reported to not run on Minimig.