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why write protect still works

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Offline sergoreg

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why write protect still works
« on: 03 / August / 2008, 23:02:09 »
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Hi,
Sorry maybe this question was I asked before, but I could not find an answer:(

Why there is a need for write protect be turned on to run CHDK on (SD870, DryOS cameras)?
And most importantly how camera still can record images (checked myself) when the switch is on?
even though the manual says it's impossible?
Is the firmware just ignore it?

Other unrelated question:
What is the minimum memory speed for shooting 640x480 30 fps on SD870 ?
Manual recommends format SD card on the camera, but I have to do on a computer to load CHDK.

Best regards,
sergoreg.


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Offline fe50

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Re: why write protect still works
« Reply #1 on: 04 / August / 2008, 03:30:26 »
Hello & welcome sergoreg !

Quote from: sergoreg on 03 / August / 2008, 23:02:09
...Why there is a need for write protect be turned on to run CHDK on (SD870, DryOS cameras)?
And most importantly how camera still can record images (checked myself) when the switch is on?
even though the manual says it's impossible?
Is the firmware just ignore it?
A feature of the Canon cameras to load firmware updates; when the card is locked, the Canon firmware loader loads the CHDK from a bootable card like  a Canon fw update file, that's the way we can take control over the camera. Canon is using a new encryption method on DryOS cameras, the "old" method with the firmware update menu item doesn't work - the encryption isn't decoded yet.

The write protection on SD cards is only done by software, readers (also the reader in the camera) look to the physical position of the lock switch and then handle it by software.

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What is the minimum memory speed for shooting 640x480 30 fps on SD870 ?
You can set up the video quality / bitrate in the video parameters menu, check the lowest setting to measure this out (bitrate 0.25-3.0 / quality 1-99 where 84 is Canon's value for best quality on most cameras).

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Manual recommends format SD card on the camera; but I have to do on a computer to load CHDK.
With cards <= 2GB you can do it in the camera, 4GB cards must be formated with (non-standard) FAT16, bigger SDHC cards need special partitioning & multi partition suppport in CHDK, that have to be done with a card reader.
After formating you have to prepare the SD card again (make card bootable & copy CHDK to the card), 2 mouse clicks under windows with the Cardtricks.
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Offline sergoreg

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Re: why write protect still works
« Reply #2 on: 04 / August / 2008, 20:09:02 »
Thank you, fe50
for a quick reply
It's SD870 is actually my first camera, but I do have some background with x86 assembly.
regarding the minimum memory bandwidth what does it have to be in terms of XXX rating,
I don't think memory manufactures disclose exact numbers  anyway.
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