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[DPRG] webcam robot vision limitations
Subject: [DPRG] webcam robot vision limitations
From: Triffid Hunter
triffid_hunter at funkmunch.net
Date: Wed Jun 27 00:12:42 CDT 2007
On Wed, 27 Jun 2007, Next Kiwi wrote:
>
> Hi Chris, that is interesting an you are likely right. Just a question here
> as I work with cameras and wondered why I have never used SD cards for
> real-time stuff.
>
> Correct me if I am wrong but here goes. SD flash card typical is 100 to 300K
> writes for a cards life time. So 300K/15fps will give 20K seconds (333
> minutes) worth of storage before the limit is hit. Is that right ?
yes, but only if you write every frame to the same location in flash.
Modern flash filesystems (and some devices) do wear-levelling, where it
writes each update to the next page so each page is used the same number
of times.
This means you get 100k writes * (1gb/2k=524288 pages) = 52429M page
updates / (800*600/2k = 235 pages per frame) / 15 frames per second =
about 6 months for raw monochrome 800x600, 15fps on a 1gb flash device
with 2KB pages.
> I think RAM may be a better medium and may be faster to read/write too.
this is true, but it's also volatile so it's not suitable for all
applications. Only dram is available in those sizes for reasonable cost,
and it takes a lot more power than sram to maintain its data so battery
backup is of limited usefulness.
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