I just got a BeagleBone Black, and I've been fumbling around the
documentation for almost 3 days, and still don't feel I know how to get
started doing what I want to do....
Goal: I want to create some hard-real-time PRU functionality, create a
less-hard-real-time executive running under Linux, and link the two
together, so that I can control/monitor the functionality at the PRU level
via ethernet.
My background: I have many years of down-to-the-metal embedded systems
development, using no RTOS or an embedded RTOS. I use Windows, and I use
desktop Linux and use the terminal when I need to, but I don't have deep
knowledge of how Linux works.
Given your background, your first decision should probably be Linux or
no-Linux. There are various options to make Linux real-time, but they
start with the Linux knowledge you don't have, and generally add a layer
of complexity above that.
If you need non-real-time access to lots of resources (like USB and
Ethernet) or software stacks (Python, Ruby, web servers, node-js, and
*LOTS* more), you probably want to use Linux. If you have a well
bounded problem, don't need portability, and are comfortable talking
directly to the hardware, use CCS and run bare-metal (or spend some $$$
and use an embedded RTOS that supports the AM335x).
Where I've landed thus far: I have installed the TI Code Composer Studio on
Windows - and it looks reasonable enough. I have a TI AM335x SDK installed
on a Linux PC, and have a micro-SD with the SDK on it, but have not
installed it on the BBB. I have read tons of documentation, but nothing
that walks a newbie through the development and deployment process.
Sticking points and questions:
- I have a gaping hole in my knowledge about embedded Linux, and how to
develop and deploy applications to it. Are there any good online resources
to help me along with this? Books? Other suggestions?
There's embedded Linux and real-time Linux. They aren't the same. It
sounds like you want real-time Linux, which for the ARM means you're
looking at either the Xenomai or the PREEMPT_RT patch sets.
The Xenomai patches take control of hardware interrupts and defer Linux
IRQ processing to maintain hard-real-time. The PREEMPT_RT patches rely
on the SMP support built into the Linux kernel to provide good real-time
performance. PREEMPT_RT works well for chips with quality SMP capable
drivers (ie: x86), but falls a bit flat in the ARM world with a *LOT* of
vendor-provided drivers that are not even SMP safe, much less SMP optimized.
- I am going down the path of installing the TI SDK, but I don't even
know if this is the right thing to do. How do I evaluate my options in the
context of my objectives?
Provide some more details about what you're trying to do and we can
probably make some specific recommendations.
There are prepackaged Xenomai kernels available if you want to go that
route. I personally work with Machinekit, which uses the Xenomai kernel
running on the ARM for decent real-time performance, and code running in
the PRUs to generate step/dir and PWM outputs for controlling 3D
printers or similar CNC machines. There is a hard real-time HAL layer
provided with Machinekit that might make it easy to code what you're
wanting to do, and pre-built images available with the kernel and
everything already installed:
http://www.machinekit.io/
http://elinux.org/Beagleboard:BeagleBoneBlack_Debian#BBW.2FBBB_.28All_Revs.29_Machinekit
- Can I do PRU development and make it run on and with the Debian distro
that is factory installed on the BBB?
Absolutely. There are lots of PRU examples floating around. The
default BeagleBone image provides device-tree support for the PRU as
well as the PRU assembler (pasm), a C compiler, and a PRU Forth.
