Date: Tue, 23 Jan 1996 15:59:42 -0600 From: Jim Lowe <james@miller.cs.uwm.edu> To: marino.ladavac@aut.alcatel.at Cc: hackers@freebsd.org Subject: Re: Amancio's tv program with capture! Message-ID: <199601232159.PAA21997@miller.cs.uwm.edu>
next in thread | raw e-mail | index | archive | help
> Is it possible to mmap() something to the address returned by shmat()?
>
> Something like:
>
> shmaddr = shmat( shmid, NULL, 0 );
> mapaddr = mmap( shmaddr, ... );
>
> I haven't got a slightest clue about this approach.
>
> /Alby
>
Yes, and no. One should be able to do this, but the frame grabber
can't write into this shmaddr. It has its own constraints to deal
with.
The driver writes to a contiguously, wired down region of memory
that is allocated at bootup time. So we do something like:
i = open("/dev/meteor0", O_RDONLY);
total_size = ((geo.columns*geo.rows*geo.frames*depth+4095)/4096)*4096;
data_addr=mmap((caddr_t)0, total_size + 4096, PROT_READ,
MAP_SHARED, i, (off_t)0);
Now we want X to be able to access this so I tried something like:
ximage = XShmCreateImage(display, fc_visual, depth,
ZPixmap, NULL, $shminfo, vid_stream->mb_width,
vid_stream->mb_height);
shminfo.shmid = shmget (IPC_PRIVATE,
ximage->bytes_per_line * ximage->height,
IPC_CREAT | 0777);
shminfo.shmaddr = ximage->data = shmat(sminfo.shmid, data_addr, 0);
xhminfo.readOnly = True;
XShmAttach(display, &shminfo);
XShmPutImage(display, ...);
If I do a
ximage->data = shmat(sminfo.shmid, 0, 0)
and then a
bcopy(data_addr, image->data, size);
XShmPutImage(display, ...);
It works just fine.
I am not sure how one is suppose to mark a previous defined
memory region as shared and get an id for it to pass along
to X. The whole object is to avoid the ``bcopy'' because
we are talking anywhere from 5-35MBytes/second of data we
have to copy. From the tests that I have done, I can only
get about 40Mbytes/second mem<->mem bandwidth (Triton chipset),
which doesn't leave much (if any) room for anything else.
-Jim
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199601232159.PAA21997>