Interrupts are essential features of microcontrollers that allow them to respond to external or internal events. However, testing and debugging interrupts can be challenging, as they require special tools and techniques. In this article, you will learn how to use a debugger to test a microcontroller's interrupts and verify their functionality.
An interrupt is a signal that causes the microcontroller to stop its current execution and jump to a predefined function called an interrupt service routine (ISR). The ISR performs the necessary actions to handle the interrupt and then returns to the original program. Interrupts can be triggered by various sources, such as timers, sensors, buttons, communication protocols, or software instructions.
The logic interrupt also could be saying as the execution of a sub routine scanning. Basically the PLC will execute the algorithm on main routine from top to down and there will be some sub routine attached to any rung that will be execute if the requirements is satisfy.
Interrupts allow the flow of program execution to be modified by an external event asynchronously. When an interrupt occurs (and is accepted), the execution of the current program is suspended. In most cases, the interrupted program resumes. When an interrupt occurs, program execution jumps directly (almost) to the code required to ‘service’ the interrupt. A special routine executes to service the interrupt, and this routine is called an interrupt handler or interrupt service routine (ISR). Interrupts allow a very fast response of a program to external events (low latency) and may simplify programming when interfacing with external devices with strict timing requirements. They also allow systems to operate in ‘real time.’
Testing interrupts is important to ensure that the microcontroller can handle different scenarios and perform the desired tasks. For example, if you are designing a device that uses a button to switch between modes, you need to test that the interrupt triggered by the button works correctly and does not interfere with other functions. Testing interrupts can also help you identify and fix bugs, optimize performance, and improve reliability.
Testing logic interrupt is crucial to ensure the main algorithm will be execute once the sub routine is completely scanned. Another thing that also important is to understand the PLC habits scanning, as some of PLC has different way of scanning, it could be from down to top of Algorithm.
A debugger is a software tool that allows you to control and monitor the microcontroller's operation. You can use a debugger to set breakpoints, step through code, inspect variables, modify registers, and watch expressions. To use a debugger, you need a hardware device that connects the microcontroller to your computer, such as a programmer, a debugger, or an emulator. You also need a compatible software environment, such as an integrated development environment (IDE) or a command-line interface (CLI).
Breakpoints are locations in the code where you want the debugger to pause the execution and give you access to the microcontroller's state. You can set breakpoints in different ways, depending on the debugger and the code. For example, you can set breakpoints by clicking on a line number, by entering a function name, by specifying a memory address, or by using a conditional expression. You can also enable or disable breakpoints, delete them, or modify them.
To test interrupts with breakpoints, you need to set one or more breakpoints in the ISR or in the main program. Then, you need to run the code and trigger the interrupt source, either manually or automatically. The debugger will stop at the breakpoint and show you the relevant information, such as the interrupt vector, the stack pointer, the registers, and the variables. You can then check if the interrupt is handled correctly, if the ISR performs the expected actions, and if the main program resumes normally.
Interrupt handling typically involves using a debugger like TRACE32, which interfaces through JTAG or Nexus. Load the symbol and debug information, usually found in the ELF file. Set breakpoints and enable interrupts at the ISR location. Configure watch windows to monitor variables or registers. The debugger stops at breakpoints, showing key information interrupt vector, stack pointer, registers, and variables, then confirm interrupt sources by checking status registers like eTPU's ISR in NXP MPC5777C and adjust priorities via registers like IVPR and SRS for interrupt handling.
Sometimes, breakpoints can interfere with the timing or the logic of the interrupt handling, especially if the ISR is time-sensitive or if multiple interrupts occur simultaneously. In that case, you can use other debugger features to test interrupts without breakpoints. For example, you can use watchpoints, which are expressions that trigger the debugger when they change value. You can also use tracepoints, which are locations in the code where the debugger logs data without stopping the execution. You can also use logic analyzers, which are hardware devices that capture and display the signals on the microcontroller's pins.