I was recently reviewing some FIFO based serial TX/RX circular buffer code that I thought was buggy in the FIFO part. Since the FIFO was entwined with the ISRs, it was hard to test in isolation. I looked around at some other FIFO implementations for PIC and AVR, and all of them did the same thing, including duplicated all of the FIFO code for every serial port implemented. It seemed to me that it would be better to have the two activities separated to provide better re-usability and test-ability.
Back when I was working on PCI audio drivers, I thought the same thing. Everyone wrote their sample FIFOs directly into the ISR functions in the driver. Back then, I seperated my FIFO out into a separate reusable module that could be tested thoroughly from user land. I grabbed that to use on my current project, but it depended on malloc and free, something notably missing on a lot of 8 bit micro controllers. Also, it would result in extra function call overhead, which is not good in ISRs on PICs (very limited hardware call stack).
Anyway, after debugging the FIFO in my ISRs, I decided to extract it all out into a file of just that code. Then I transformed those functions into macros to do away with the function call overhead.
Here is draft 1, if it is of any use to anyone, and even if it isn’t I certainly wouldn’t mind review/commentary.
I could wrap the globals into a struct, but then I still would need a custom struct for each instance to change the size of the array at run time, unless I required a global struct, and MAKE_FIFO inserted a pointer to a global array…
I’m not sure, which might be better.
Also, if you were to need 32bit elements instead of 8 bit elements, just change the type in MAKE_FIFO.
- BUF_SIZE(prefix)
- GET(prefix, value)
- PEEK(prefix, value)
- NEXT_IN(prefix)
- FLUSH(prefix)
- IS_EMPTY(prefix)
- IS_NOT_EMPTY(prefix)
- KBHIT IS_NOT_EMPTY
- AVAIL IS_NOT_FULL
- RESET - like flush, but also resets ovfl flag.
- Get rid of _len variable.
Add an argument to MAKE_FIFO of type.