EPI Read Cycle in TM4C129DNCPDT

Hi Amit,

Thank you for responding to my query.

Please refer to following code snippet in blue font.

inline uint8_t
EPIWorkaroundByteRead(uint8_t *pui8Addr)
{
    uint32_t ui32Scratch;
    uint8_t ui8Value;

    __asm
    {
        //
        // Add a NOP to ensure we don’t have a flash read immediately before
        // the EPI read.
        //
        NOP

        //
        // Perform the read we're actually interested in.
        //
        LDRB ui8Value, [pui8Addr]

        //
        // Read from SRAM to ensure that we don't have an EPI read followed by
        // a flash read.
        //
        LDR ui32Scratch, [__current_sp()]
    }

    return(ui8Value);
}

Above code snippet has been excerpted from file epi.h available in TM4C129DNCPDT peripheral software library.

Function inline uint8_t EPIWorkaroundByteRead(uint8_t *pui8Addr), reads a byte of data from external peripheral connected to EPI interface of MCU.

The line of code on following lines in blue font excerpted from above function, is what i am referring to as "Dummy Read Cycle".

//
// Read from SRAM to ensure that we don't have an EPI read followed by
// a flash read.
//
LDR ui32Scratch, [__current_sp()]

My questions about the line of code written above are as follows :

1.   What is purpose of this line of code ?

2.   Could this line of code be omitted from the function ?

3.   What would be the repercussions of omitting the line of code from the function ?

4.   Does the line of code generates read transaction on parallel bus of EPI peripheral ?

5.   is any peripheral register accessed after executing the line of code ?

Thank you,

Sunil Sawant

Hello Sunil

Did you read the errata document for EPI#01? This code is the workaround code for the issue EPI#01.

Regards

Amit