Re: Trying to DMA data from PCI bus to IDE
phil_at_armstrong.invalid
Date: 08/20/03
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Date: Wed, 20 Aug 2003 09:50:13 +0100
In article <5ff867d6.0308191032.6fc61c36@posting.google.com>,
LegoGT <legoburns@yahoo.com> wrote:
>I'm trying to use a PC104 IO board that utilizes the PLX PCI9080 chip
>to handle DMA transfers across the PCI bus to the rest of the PC104
>stack. I've been able to take the data from the IO board, DMA it to
>memory, and then use the regular Linux functions to write it to the
>hard drive. Even though my drive is using the highest UDMA settings
>(ATA66 for a solid state drive) and have tweaked the hdparm, it seems
>as if there's too much Linux file overhead involved to get it any
>faster -- especially because I'm trying to "stream" lots of data
>really fast for an extended time period to anywhere on the drive
>(I'll deal with the partitions and FAT later). It seems as if Linux
>"waits" for about 5sec before it starts to write ANYTHING to the
>drive. Even if I turn off all of the caching settings in hdparm.
>This tells me that it's a caching technique specific to the kernel
>that *hopefully* I can turn off.
hdparm has nothing to do with the kernel's in memory caching of disk
buffers. Look at the values in /proc/sys/vm/ -- you can tweak these to
make the kernel more aggressive about writing out dirty data.
It sounds like you should really be using raw devices instead of
buffered ones. Try setting up a raw device pointing to your disc
partition and writing the data to that instead. I presume you've made
sure that your solid state device is capable of sustained writes at
the speed your data is coming in :)
>So, Does anyone know of/have ideas about a way to configure the
>PCI9080 chip or similar chip to DMA that data to a single address in
>memory? I've set up the drive to receive data via DMA data and write
>it to specific sectors so then the PCI9080 would need to be "pointed
>to" a single location in memory (0x1f0 to be exact for the primary
>IDE). I've been trying everything, but I think there might be
>something having to do with how Linux maps the addresses in virtual
>memory vs. physical for the PCI9080.
>
>Effectively, it should be set up to pull the data from the PCI source
>(a FIFO address on the IO board) and perform a DMA transfer to memory
>while NOT incrementing the destination address.
Er. Can't you do PCI transfers directly between the two devices? No
memory access required then. My knowledge of PCI programming is
pretty sketchy, so I'm not sure how feasible this is in your case.
cheers,
Phil
-- http://www.kantaka.co.uk/ .oOo. public key: http://www.kantaka.co.uk/gpg.txt
- Previous message: Vijay Kumar Zanvar: "problem with ioctl"
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