DOSBox DOS timer overrun bug \ VOGONS

DOSBox DOS timer overrun bug

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First post, by Sika

Posted on 2013-04-19, 16:10

Sika Offline

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Rank: Newbie
Posts: 2
Joined: 2013-04-19, 15:32
Location: Siegen, Germany

Hi community, first my highest acknowledgement for such a superb development.

I have programed many years under DOS using Turbo Pascal. Until about 15 years years ago professionally, lately just for my private use. I know DOSBox is ment (mainly) for games, but running my old DOS software under Win7-64bit in a DOS box is to me like playing games.

I'm not sure if this might concern real games as well, but I found that the DOS timer interrupt (responsible for time and date under DOS) does not consider the daily overrun from 23:59:59 to 00:00:00. Instead it will count on and time will then display hours greater 24, the day does not change.

DOS interrupt calls to reset the time don't change the time in DOSBoxs too. The only way I found to change the time is to write directly to the DOS storage of the timer counter at address $40:$6C.

Thanks,
Joerg

Reply 1 of 3, by ripsaw8080

Posted on 2013-04-19, 16:46

ripsaw8080 Offline

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Rank: DOSBox Author
Posts: 5083
Joined: 2006-04-25, 23:24

Midnight rollover is implemented in SVN. Setting the time with INT 21/2D is intentionally blocked in DOSBox; but as you've noticed it is possible to change the BIOS timer ticks directly, and it can also be done with INT 1A/01. INT 21/2D in SVN allows the time to temporarily be set to 00:00:00 because some games (usually ones made with some flavor of BASIC) do this as a crude way to measure elapsed time.

Reply 2 of 3, by Sika

Posted on 2013-04-19, 17:53

Sika Offline

Rank Newbie

Rank: Newbie
Posts: 2
Joined: 2013-04-19, 15:32
Location: Siegen, Germany

Thanks a lot, it really works 😀

I used DOSBox SVN r3827 and installed the required MSVCP100.dll using "Microsoft Visual C++ 2010 SP1 Redistributable Package" directly from the Microsoft download page.

This is a really cool project.

Thanks,
Joerg

Reply 3 of 3, by macchese

Posted on 2013-09-25, 10:56

macchese Offline

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Rank: Newbie
Posts: 1
Joined: 2013-09-25, 10:52

Hi,
I need to handle correctly time and date, could I use the trunk SVN or I need some specific version/tag/branch instead? tahnk a lot in advance

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