synchronization between two tasks

Question

This is actually a design question for firmware in an embedded system I have two ISRs (of same priority) executed independently . These ISRs are triggered when the h/w generates data. I want a mechanism which must be put in place to synchronise between task1 and task2. task 2 must know about the certain values calculated in task1 which must then be taken into account while computing certain values in task2. I don't have OS primitives to use ie the system does not have any Operating system. Task1 is executed within the context of ISR1 and task2 within the context of ISR2. The processor which we use is a STMicroelectronics 32 controller

EDIT: additional info The processor is connected to certain IPs which trigger interrupts when they are ready with data. These IPs act as type of Accumulators on input streaming frame data.

Answer 1

I wouldn't do heavy processing in interrupt context, just read the data and set a flag.

The flags can then be checked in a simple scheduler in the main loop to execute the tasks as necessary. So tasks can't interrupt each other and can't see inconsistent output of the other task.

A task could also set such a flag to activate another task. E.g. Task1 could activate Task2 because Task2 needs values from Task1.

For the data that is read in the ISR you need some buffer. Depending on the timing of your incoming data that might be a ring buffer or a double buffer.

Answer 2

• Disable interrupts before reading or writing to the shared values
• Re-enable interrupts after reading or writing to the shared values