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Joined: Apr 2012
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Pernod Online Content OP
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Finally implemented character rounding:
Old

New

This also includes a few fixes to the roms, note corrected 'D'.

I'm using a teletext engineering test image for testing and are still some obscure control characters not being handled correctly. Hope to get it submitted for this months release though.


BBC Model B, ATPL Sidewise, Acorn Speech, 2xWatford Floppy Drives, AMX Mouse, Viglen case, etc.
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Nice! I hope it gets submitted for 0.167.

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Pernod Online Content OP
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Completed my saa5050 updates, here's some screenshots to compare old/new with the real thing.
old

new

real

All control codes are now handled correctly.
It is still not perfect though, if you look closely you'll notice the bottom scanline is missing from each character row, most noticeable on y and g. This is not a regression as the old screenshot shows this too. I'll get back to it when I understand more of video handling.


BBC Model B, ATPL Sidewise, Acorn Speech, 2xWatford Floppy Drives, AMX Mouse, Viglen case, etc.
Joined: Apr 2012
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Pernod Online Content OP
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So, I broke malzak and p2000t with this update. I did test them before submitting but obviously not with what actually got submitted.

This has been quite puzzling but I think I now have a conclusion smile

The saa5050 outputs characters of 20 scanlines but the mc6845 has R9 set to 18 and so outputs 19 scanlines (I had fudged saa5050 to accommodate this and so broke malzak etc). This explains why I'm missing the bottom scanline in the above screenshots.

I've now been reliably informed the bbc actually uses the hd6845 http://www.cpcwiki.eu/imgs/c/c0/Hd6845.hitachi.pdf and on page 90:
Quote:
Maximum Raster Address Register (R9) *
This is a register used to program maximum raster address within 5-bit. This register defines total number of rasters per character including line space. This register is programmed as follows.

Non-interlace Mode, Interlace Sync Mode
When total number of rasters is RN, RN-1 shall be programmed.

Interlace Sync & Video Mode
When total number of rasters is RN, RN-2 shall be programmed.

So in interlace mode it would output 20 scanlines when R9 is 18.

I see our implementation of hd6845 doesn't implement this so will try to fix this.

I also noticed we have a MCFG_MC6845_INTERLACE_ADJUST only used in apricot. Is this a workaround for my issue and the apricot should actually use a fixed hd6845?


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Probably related yes. Without the hack the apricot displays 350 instead of 400 lines.

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