Synchronizing between ISR and main code

Hi eliben,

> What is the best way to ensure safe access to shared data between an

> ISR and the main code ?

That depends on what you are trying to do -- there's usually not a single "best way".

> Is disabling interrupts during the main's code reading of the data the best option ?

In most cases, no. This usually leads to those "mysterious" bugs that show up when

baud rates, cpu clocks, etc. change.

> What are the common guideline when dealing with data synchronization

> in ISRs for Nios ?

Here's a good reference: http://www.xml.com/ldd/chapter/book/ch09.html#t8 (http://www.xml.com/ldd/chapter/book/ch09.html#t8)

A very simple and common technique is to use a circular buffer. The size of the buffer can

be adjusted to meet your requirements ... provided you have adequate memory resources.

Here's a basic overview:

1. The isr reads a "put" pointer, and writes its data. Then updates the put pointer.

2. The app compares the put pointer to a "get" pointer, when unequal, there is data.

3. The app reads (copies, consumes, whatever) the data, then updates the get pointer.

Regards,

--Scott