I am using Beagle Bone Black with Arch Linux ARM OS to communicate with ltc-6804 chip via SPI port. I have came to a point that the interrupt from the OS in the middle of sending read command and receiving measured values causing a trouble for me to get a valid measurement from the chip. Is there any way to "protect" the part of the code being interrupted on the run? In the other words, let the send and read section complete without any interruption.
Electronic – Protect user space critical section from interrupt
interruptslinux
Related Solutions
Can be done with a simple transistor and two resistors. When the 3.3v pin is pulled high, the arduino's interupt pin is pulled low.
simulate this circuit – Schematic created using CircuitLab
Several issues:
- This is the poster case for why you need to carefully chose which pins of the micro will be used in what ways. "I'm using them for interfacing to an LCD" is no excuse. Go use some other pins for the LCD that don't also have a special hardware function you need. Assign pins that use special hardware functions first, then assign general I/O to whatever pins are left over.
- The PIC 16F873A is quite old. There are probably newer PICs with the same footprint that have a lot more I/O capability, possibly including more interrupt on change pins.
- There are other ways to cause a interrupt, such as the INT pin specifically for that purpose, the CCP inputs, and even timer clock inputs if you're clever. Some of these may use up other hardware just to get the interrupt, but there is no harm in that if you weren't going to use that hardware anyway.
- See point one. Assign the pins properly. This really should be obvious.
Best Answer
This is a different approach to your problem, and is not about working within Linux. Instead it is about using other BeagleBone Black resources to solve the problem.
As well as the ARM Corex-A8, the BeagleBone Black also has two more processors, called Programmable Real-Time Unit Subsystem and Industrial Communication Subsystem (PRU-ICSS), often just PRU.
The two PRUs run independently of the ARM running Linux, and so are not affected by Linux scheduling; they won't be interrupted or pre-empted by Linux.
PRUs are intended for real-time processing, and have access to all I/O. They are RISC cores each running at 200MHz, so should be plenty fast enough, and be able to do anything you need. You could dedicate one to your SPI communication task.
They can be programmed in C or assembler. There are several useful articles on the web this one on Hackspace has useful links to key examples and technology. IIRC there are examples showing how to the main 'Linux processor' interacts with a PRU.
Edit:
This is a course on using the PRU.