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Is there software that you can run on a Pi that emulates a microcontroller that uses the Pi's I/O pins? That might be an easier to use way to prototype, with th

Is there software that you can run on a Pi that emulates a microcontroller that uses the Pi's I/O pins? That might be an easier to use way to prototype, with the ability to restart the microcontroller while the host is still functioning. It could also be a nice way to emulate additional IoT devices in a neat little package, which might help simulations and debugging.

jimmywanger 9y ago
I think the problem is the realtime. You can certainly write software that emulates a microcontroller on the Pi, but the problem is that it can't guarantee timing, since it's running on Linux fundamentally, and other processes can pre-empt it. For certain things it doesn't matter as much, such as for a door lock or something like that. Then you gotta worry about power consumption, since running cables to your lock is problematic, and it has to run on batteries for months at a time. That's a reason why realtime controllers can't run on Linux - if you were controlling an industrial robot that controls welding temperatures and times, even like 300 ms off can drastically affect the finished product with fit and finish and metal heat treating. "This whole batch of parts worth hundreds of thousands of dollars went bad!" "Well, the network is down, and the robot controller was busy trying to reconnect to the network, so that's why the welds were formed over 300 ms more than they should have been." That can't cut it in industrial applications.
dreamcompiler 9y ago
I think you're asking about writing "direct to the metal" software on the Pi, which I hope someone will address here. To answer your question indirectly, there are ways to bend Linux to do realtime like rt-preempt [0] but it doesn't go as far as RTLinux [1], which virtualizes the entire OS to run under a hypervisor that is essentially just a service routine for a hardware nonmaskable interrupt. Linux isn't even aware it's being preempted in this model. It's a beautiful approach, but RTLinux was proprietary and hard to write code for (because, interrupt handler), so it never achieved much traction. [0] https://rt.wiki.kernel.org/index.php/RT_PREEMPT_HOWTO https://rt.wiki.kernel.org/index.php/RT_PREEMPT_HOWTO [1] https://en.m.wikipedia.org/wiki/RTLinux https://en.m.wikipedia.org/wiki/RTLinux

jimmywanger 9y ago

I think the problem is the realtime. You can certainly write software that emulates a microcontroller on the Pi, but the problem is that it can't guarantee timing, since it's running on Linux fundamentally, and other processes can pre-empt it. For certain things it doesn't matter as much, such as for a door lock or something like that. Then you gotta worry about power consumption, since running cables to your lock is problematic, and it has to run on batteries for months at a time. That's a reason why realtime controllers can't run on Linux - if you were controlling an industrial robot that controls welding temperatures and times, even like 300 ms off can drastically affect the finished product with fit and finish and metal heat treating. "This whole batch of parts worth hundreds of thousands of dollars went bad!" "Well, the network is down, and the robot controller was busy trying to reconnect to the network, so that's why the welds were formed over 300 ms more than they should have been." That can't cut it in industrial applications.

dreamcompiler 9y ago

I think you're asking about writing "direct to the metal" software on the Pi, which I hope someone will address here. To answer your question indirectly, there are ways to bend Linux to do realtime like rt-preempt [0] but it doesn't go as far as RTLinux [1], which virtualizes the entire OS to run under a hypervisor that is essentially just a service routine for a hardware nonmaskable interrupt. Linux isn't even aware it's being preempted in this model. It's a beautiful approach, but RTLinux was proprietary and hard to write code for (because, interrupt handler), so it never achieved much traction. [0] https://rt.wiki.kernel.org/index.php/RT_PREEMPT_HOWTO https://rt.wiki.kernel.org/index.php/RT_PREEMPT_HOWTO [1] https://en.m.wikipedia.org/wiki/RTLinux https://en.m.wikipedia.org/wiki/RTLinux