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Old 07-25-2012, 03:51 AM   #1
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How to interact with the processor from within linux, read a GPIO port, use timers...


I am trying to decide if it will be a simple thing to interact with the TI processor of the beaglebone from within linux. Will it require kernel modifications, or the does the standard kernel expose the processor peripherals? Can I get code to run on the chip at the same time linux is running?

I haven't done a kernel before, would that be the best way to expose the peripherals to the linux environment? Would it be similar to writing RTOS routines?

This is a bit outside my comfort zone I'm trying to get the benefit of linux with the control of an RTOS. :-)
Old 07-27-2012, 11:12 AM   #2
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The Linux kernel code runs on the CPU. Userspace applications also run on the CPU. A CPU capable of supporting Linux has the facility to partition the kernel code and data space from userspace code and data, and also to ensure that each userspace process is confined within boundaries prescribed by the OS (kernel). CPUs often include peripherals built onto the CPU silicon, and/or there are external peripheral chips. Accessing those is usually the domain of kernelspace code. The kernel provides a means of access to the peripherals by userspace code through device drivers. It is also possible to create userspace access to peripherals, commonly called userspace drivers. This always requires root privileges, and is commonly done as application-specific code, not intended for any kind of shared access by other applications. Some developers use it as a step in the learning process while developing a full and proper kernel mode driver for a particular peripheral device.

There are extensions to Linux that provide real-time functionality, but otherwise Linux is not a RTOS. It sounds like you may be familiar with something like vxWorks, which is a realtime OS, but does not use protected mode on the CPU, and therefore does not embody the concept of kernel-mode vs usermode. That is done for performance reasons, as the use of protected mode imposes some significant overhead in CPU cycles.

--- rod.
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Old 07-27-2012, 12:01 PM   #3
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Thanks B-)

I thank you for the reply.
Your correct I'm an embedded guy but I tend to use an RTOS (currently sysBIOS) for task management only. I prefer to manage memory on my own as I get a bit better code size and I can tune performance where needed. That said its a lot of work to do anything. So I am looking to start using an OS and prepackaged hardware to provide a richer user interface. But I have some routines that need to be fast so I need access to processor itself.


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