Re: Access to DMA memory while DMA in progress?

[<Paul.Koning%dell.com@localhost>]

> On Oct 27, 2017, at 9:38 AM, Mouse <mouse%Rodents-Montreal.ORG@localhost> wrote:
> 
> ...
> I would like to read the DMA buffer while DMA is still going on.  That
> is, I have a buffer of (say) 64K and the hardware is busily writing
> into it; I want to read the buffer and see what the hardware has
> written in the memory it has written and what used to be there in the
> memory it hasn't.  I'm fine if the CPU's view lags the hardware's view
> slightly, but I do care about the CPU's view of the DMA write order
> matching the hardware's: that is, if the CPU sees the value written by
> a given DMA cycle, then the CPU must also see the values written by all
> previous DMA cycles. 

I'm not sure if that requirement is necessarily supported by hardware.  For example, in machines that have incoherent DMA, I would think it isn't.

	paul