UART receive buffer writing and reading

Question

I'm making a simple communication between an ARM mcu and a GSM module.

The problem I'm facing is how to deal with simultaneously writing and reading to and from the FIFO buffer.

Due to scale of the program I have a big buffer array of 1000 bytes long.

At the moment an interrupt is triggered every time a byte received at UART's data register and the interrupt's routine is filling my 1KB FIFO.

My read routine calculates the available data in FIFO and copies some of the data in a second buffer for further processing.

The interrupt routine stops to put more data when no more space is left in FIFO buffer, to prevent overwriting on reading pointer in the cases my main program didn't have the time to process the data.

Now I'm trying to find the best solution to prevent overwriting on reading pointer while interrupt routine never stops to put data. Is there any solution for this or overwriting is inevitable?

Answer 1

On UART receive event:

    FIFO[Wr_pointer]= UART_Char;
    WR_Pointer++;
    WR_Pointer & = 3FF;// FIFO[1024] roll over 1022..1023...0...1...2
    if WR_Pointer==RD_Pointer then
        Overrun= true;
    else
    {
        SizeFIFO = (WR_Pointer - RD_Pointer);
        SizeFIFO & = 3FF;
    }

Circular buffer example. There is no need to copy data from FIFO to another location since the data are just overwritten.

In the application:

SizeFIFO_temp = SizeFIFO; //you don't want a bug when ISR will insert new data while processing the buffer
for i=0 to SizeFIFO_temp  do
{
   Data[i]=FIFO[RD_Pointer]; //it's all up to you how you process the FIFO's data
   RD_Pointer++;
   RD_Pointer &= 3FF; 
}
SizeFIFO = (WR_Pointer - RD_Pointer);
SizeFIFO & = 3FF;

Answer 2

The problem I'm facing is how to deal with simultaneously writing and reading to and from the FIFO buffer.

Sequential Not parallel.

Now I'm trying to find the best solution to prevent overwriting on reading pointer while interrupt routine never stops to put data

Code must never exist always in the ISR(generally,depends on application). You need time to copy data, process data,reset flags and various states etc before a new request can be processed. If you are always receiving data when will you do the rest?.

1.When an interrupt occurs: Disable the interrupt(many forget to do this)

2.Since you have a 1K Buffer(Waste of memory,implement a circular buffer of smaller length),copy the data to a buffer and watch a counter when the minimum number of bytes required for a processing is received. Dont forget to enable the ISR again and reset the counter before leaving ISR.

3.When the minimum number of bytes required for a processing is received,process the data.

Alternatively, you can make the uC as the master that polls the GSM for data when needed so that you have control, instead of GSM sending you data always.