From:	"Tims News" <ttodd_nospam AT cct DOT co DOT uk>
Newsgroups:	comp.os.msdos.djgpp
Subject:	DMA, Pointers and Physical Memory
Date:	Fri, 11 May 2001 11:42:10 +0100
Message-ID:	<989577210.22969.0.nnrp-02.c30b1810@news.demon.co.uk>
NNTP-Posting-Host:	[195.11.24.16]
X-NNTP-Posting-Host:	[195.11.24.16]:195.11.24.16
X-Trace:	news.demon.co.uk 989577210 nnrp-02:22969 NO-IDENT [195.11.24.16]:195.11.24.16
X-Complaints-To:	abuse AT demon DOT net
X-Priority:	3
X-MSMail-Priority:	Normal
X-Newsreader:	Microsoft Outlook Express 5.00.2014.211
X-MimeOLE:	Produced By Microsoft MimeOLE V5.00.2014.211
Lines:	55
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp
Reply-To:	djgpp AT delorie DOT com

Hi,

I am currently working on MultiBus II Message Passing and have hit a small
problem with the DMA transfer.

I need to convert a standard pointer (eg. struct mystruct* pInstance) to a
PHYSICAL memory address.  This is not the address of the data to be
transferred (that seems well documented in the FAQ - although I haven't
tried the code yet), this is for the DMA command block.

The code I have at present, does not seem to be working - can anybody help
me please.  Also, PLEASE PLEASE PLEASE, if you send me a "read faq entry n"
could you please also include the link for the FAQ to which you refer - as
far as I can make out there are a number of (all sleightly) different ones
around - Thank You :)

By means of further explanation, below is a snippet of my code:


main()
{

struct cb_short1*    pCmd;

cb_short.info=some_stuff;
AdmaStart(1,pCmd);

}

void     AdmaStart(UINT8 chan, struct cb_short1* pCmd)
{

UINT32  Physical;
UINT16  Selector;

// Convert pointer to physical memory location
  Selector = *((UINT16*)(((UINT8*)(&pCmd))+4));
  __dpmi_get_segment_base_address((UINT32)Selector, &Physical);
  Physical += *((UINT32*)(&pCmd));

// Address of command block
  outportb(CPRL +(CHAN_SEP*chan), Physical &0xFF );
  outportb(CPRH +(CHAN_SEP*chan), (Physical>>16) &0xFF );

// GO!
  outportb(GCR, 1<<(chan+4) |0x0A);

}



Tim
=%¬}

- Raw text -