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Newsgroups: comp.os.msdos.djgpp
Date: Fri, 18 Aug 2017 03:50:50 -0700 (PDT)
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Subject: Can I use transferbuffer temporarly a for short DMA transfer?
From: "RayeR (glaux AT centrum DOT cz) [via djgpp AT delorie DOT com]" <djgpp AT delorie DOT com>
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To: djgpp AT delorie DOT com
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Hi,
I need to do one IDE busmaster DMA tranfer. For this purpose I need a 512+8B buffer in physical memory - I have to fill bussmaster PDRT IO register with physical address of buffer where I put PDR entry and data. 
So it seems to me the easiest way is to use __tb, where I can copy my structures and data via dosmemput and then start DMA transfer by writting to IO registers.
But I don't know how long my data in transferbuffer? Is it shared for some DJGPP functions like if I do a printf or anything calling a DOS it may get overwritten?
Or should I rather allocate dos memory block separately?

The DMA buffer must fulfil 2 conditions: 
1) phys. address must be word aligned - probably OK, AFAIK dosmem is allocated in paragraphs
2) buffer cannot cross over 64kB boudary, e.g. FFF0h + size 512B is wrong, FE00h + size 512B is OK.
Should I care about 2nd condition myself?