VGA emulation problem \ VOGONS

VGA emulation problem

Topic actions

First post, by 4A75726120422E

Posted on 2016-02-03, 21:56

4A75726120422E Offline

Rank Newbie

Rank: Newbie
Posts: 1
Joined: 2016-02-03, 20:19

The hardware VGA in text mode allows to read the fonts loaded to RAM by sending value 2 into its Read Map Select Register:

But the DosBox emulator always reads 0 videomemory page, regardless of the RMSR register value:

The Oracle VirtualBox runs this program correctly:

Reply 1 of 3, by keropi

Posted on 2016-02-03, 22:00

keropi Offline

Rank l33t++

Rank: l33t++
Posts: 9695
Joined: 2003-09-08, 06:45
Location: Greece

welcome Jura B.

🎵 🎧 ⏳ ⚡ MK1869, PCMIDI MPU , OrpheusII , Action Rewind , Megacard and 🎶GoldLib soundcard website

Reply 2 of 3, by ripsaw8080

Posted on 2016-02-04, 00:49

ripsaw8080 Offline

Rank DOSBox Author

Rank: DOSBox Author
Posts: 5094
Joined: 2006-04-25, 23:24

keropi wrote:
welcome Jura B.

Thank goodness it isn't in binary... 😵

Anyway, I don't know about the VGA emulation in VirtualBox, but in DOSBox you need to turn off odd/even mode to read the fontmap. So, in addition to what you're doing now, write 0Ch to index 6 of port 3CEh to use the the B800h-BFFFh address window with odd/even off, then write 0Eh to index 6 to turn odd/even mode back on after you're done reading the fontmap.

Reply 3 of 3, by lightmaster

Posted on 2016-02-04, 15:24

lightmaster Offline

Rank Oldbie

Rank: Oldbie
Posts: 627
Joined: 2005-10-01, 12:09
Location: Sol III

Welcome 4A75726120422E!!

Go to top of page Go to top of page

Back to DOSBox General