How to read and write value in two different systems?

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There are many ways to do a more portable hardware access. mmap is one of them. Others are a dedicated Kernel driver that more specifically handles the hardware in question and the "uio" stuff that does not seem use specific Kernel code.[/b]

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I have checked many references. Some mentioned the idea of mailbox, which I think is very convenient.

Does it need to add an driver for uclinux to own the access to mailbox. Or any other ideas?

I will gather more information about mmap and uio, coz they are quite new to me.

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Of course it might be that the "LED" "hardware" port does not provide read access to the latches holding the state of the LEDs. IMHO that would be quite unusual. You should check the appropriate HDL implementation and maybe upgrade it.[/b]

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Thanks to your instructions. I have tried the sram, the read and write function runs well.

The problem may be the specific characteristic of LED hardware.