405EP peripheral memory access
Hi,
I am new to Linux embedded programming. I have experience programming microcontrollers and DSPs without an operating system, so I have some idea what I'm doing. Anyhow, I'm trying to use the peripheral memory bus on my 405EP CerfCube from Intrinsyc. Does anyone have an example that I can work from?
To setup the memory's timings, I need access to the DCR register. In the PowerPC datasheet it says to use assembly instructions mtdcr and mfdcr. I don't know much about assembly, but I found a kernel patch that uses these functions. So, working off this patch, I tried making a simple program to read these registers. When I run it, Linux reports an "Illegal instruction" and doesn't let me access the register.
Does access to this bus need to be done in "kernel mode"? If so, where can I find more information about writing a kernel driver? Ideally, I'd like to just open a device file and read/write to the bus.
Thanks!
-Paul
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Quoted 7 lines · Paul Miller
Hi,
I am new to Linux embedded programming. I have experience programming microcontrollers and DSPs without an operating system, so I have some idea what I'm doing. Anyhow, I'm trying to use the peripheral memory bus on my 405EP CerfCube from Intrinsyc. Does anyone have an example that I can work from?
If I remember correctly the Cerf Cube uses PPCboot/U-Boot and ships with the source on a CD.
Quoted 7 lines
To setup the memory's timings, I need access to the DCR register. In the PowerPC datasheet it says to use assembly instructions mtdcr and mfdcr. I don't know much about assembly, but I found a kernel patch that uses these functions. So, working off this patch, I tried making a simple program to read these registers. When I run it, Linux reports an "Illegal instruction" and doesn't let me access the register.
Did you make calls to the patched kernel or paste this function into your user mode program? Some registers are priviledged and only the kernel is allowed to touch them. If you had this function in a user program it won't work.
Quoted 5 lines
Does access to this bus need to be done in "kernel mode"? If so, where can I find more information about writing a kernel driver? Ideally, I'd like to just open a device file and read/write to the bus.
I wrote my first kernel driver based on an example found at
http://www.denx.de . Though It was for kernel version 2.2.x and the Motorla 8xx processor, the example was quite helpful and could still be for you. Its at the botom of the page here
http://www.denx.de/e/index1.php?head=solution-se-head&main=solution-se&subnav=solution-se-subnav&logo=logo-se&mainnav=softwarenav&bottom=bottom-se
One aproach you might take is modifying the PPCBoot source and mapping your device to a memory address and access it using the memory map functions in the kernel.
Quoted 4 lines
Thanks!
-Paul
Its going to be ruff in the begining, but it gets easier. Have fun.
Conn Clark
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Conn Clark
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Electronic Systems Technology Inc. www.esteem.com
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