Hallo Herr tom ehlert, am Dienstag, 10. August 2021 um 11:04 schrieben Sie:
>>> however if several applications want to access the same DMA controller >>> at the sam time things get complicated. there is no communication >>> between these applications. >> Exactly. That's what the API would somehow need to manage. > you can design APIs all day long, but if nobody is using these APIs > it's a bit pointless. and the BIOS certainly will not suddenly call any > DMA reservation API. > besides this, MSDOS and associated programs got along for a couple of dekades > without such an API. > that said (and I have to admit that I never did any motherboard DMA > programming), I found > http://www.dewassoc.com/support/bios/errors/dma_controllers.htm > 'Direct Memory Access (DMA) Channels > Direct memory access (DMA) channels are basically what the name implies, > the system pathway used by devices to transfer information directly to > and from memory. DMA channel problems are not nearly as frequent as IRQ > issues, > however they do occur. This is probably due to the fact that there are fewer > of them and they are used by far fewer devices. Hence they usually cause > fewer > problems with system setup. > ***Conflicts on DMA channels can often cause very > strange system problems and at times can be very difficult to > diagnose. *** > DMA channels are used most commonly by floppy and tape drives and sound > cards. > so it looks like 'it would have been nice to have a reservation API in > the 80's', but they somehow navigated around these problems. 40 years > ago. > Tom I probably found the reservation API. http://www.dewassoc.com/support/bios/errors/dma_controllers.htm DMA Request (DRQ) and DMA Acknowledgment (DACK) Each DMA channel is comprised of two signals: the DMA request signal (DRQ) and the DMA acknowledgment signal (DACK). Some peripheral cards have separate jumpers for these instead of a single DMA channel jumper. If this is the case, make sure that the DRQ and DACK are set to the same number, otherwise the device won't work! JUMPERS! anybody remembers JUMPERS (and associated problems) ? Tom _______________________________________________ Freedos-devel mailing list Freedos-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freedos-devel
