Details:

IEPx 64-bit timestamp can be incorrect when lower 32-bit data is 0xFFFFFFFC or above (at 250MHz). In this case the upper 32-bit value is updated but lower value is the old number. The issue is seen when IEP counter (IEP_COUNT_REG1 : IEP_COUNT_REG0) is read back-to-back from ICSS PRU cores.

Example 1:

1st read : 0x000000D0(Upper):0xFFFFFFFC(lower)

2nd read : 0x000000D0(Upper):0x00000028(lower)

Example 2:

1st read : 0x000000D7(Upper):0xFFFFFFFC(lower)

2nd read : 0x000000D7(Upper):0x0000002C(lower)

Example 3:

1st read : 0x000000D6(Upper):0xFFFFFFF0(lower)

2nd read : 0x000000D7(Upper):0xFFFFFFFC((lower)

As shown above, this leads to timer increment behavior that is non-monotonic or timer differences to be unusually large as in Example 3 . This is due to 1 cycle race condition when loading 64-bit value from IEPx counter.

Workaround(s):

Note: these workarounds exist in SDK9.2 and later

Workaround in C for PRU:

uint64_t timestamp = (uint64_t) (0x2E0010); 

/* Workaround starts here */

if ((timestamp & 0xFFFFFFFF) >= 0xFFFFFFFC)

{     timestamp = *(uint64_t*) (0x2E0010); } 

/* Workaround ends here */

Workaround in assembly for PRU:

 ldi32 r4, 0xFFFFFFFC ; 0-4 for 250MHz clock
    ;load 64-bit timestamp to r2:r3
    lbco &r2, c26, 0x10, 8
    qbgt skip_iep_read_errata. r2, r4
    ;re-read IEP if IEP_COUNTER_LOW >= 0xFFFF_FFFC
    lbco &r2, c26, 0x10, 8
skip_iep_read_errata: 

Workaround in C for R5F, A53:

uint64_t getIepTimeStamp64 (void)
{
    uint64_t u64Timestamp1 = (volatile uint64_t)(0x300AE010);
    uint64_t u64Timestamp2 = (volatile uint64_t)(0x300AE010);
    if (u64Timestamp2 > u64Timestamp1)
    {
#ifdef __DEBUG
        if (((u64Timestamp2 >> 32)-(u64Timestamp1 >> 32)) == 1)
        {
            /* HW errata fixed due to picking u64Timestamp1*/
            if ((u64Timestamp2 & 0xFFFFFFFF) >= (u64Timestamp1 & 0xFFFFFFFF))
           

{                 DebugP_log ("Errata fixed (1): %llx : %llx\r\n", 
        u64Timestamp1, u64Timestamp2);             }

        }
#endif
        return u64Timestamp1;
    }
    else
    {
#ifdef __DEBUG
        if ((u64Timestamp2 & 0xFFFFFFFF) < (u64Timestamp1 & 0xFFFFFFFF))
       

{             /* Adjust the IEP MSW in the case running into HW errata */             
    DebugP_log ("Errata fixed (2): %llx : %llx\r\n", u64Timestamp1, 
u64Timestamp2);         }

#endif
        /* HW errata fixed due to picking u64Timestamp2*/
        return u64Timestamp2;
    }
}