TMS320F28388D: eQEP module index detection

Hello,

I am using eQEP module on TMS320F28388D. My source of signal generates index signal gated to A and B as shown on figure 27-3 in reference manual (SPRUII0B).

I have following initialization sequence:

    Set GPIO multiplexor to QEP module

    Init GPIOs as synchronous input,

    QDECCTL[XCR] = 1

    QDECCTL[QIDIRE] = 1

    QEPCTL[FREE_SOFT] = 2

    QPOSMAX = 4095

    QPOSINIT = initialPosition // Obtained from source via serial communication

    QEPCTL[SWI] = 1

    QEPCTL[QPEN] = 1

I have problem with detecting of index signal by the CPU.

• Sometimes, it works OK.
• Sometimes, index pulse is detected one step away:
  • QEPSTS[PCEF] is set to 1
  • QPOSILAT is equal to 1 instead of 0, or 4094 instead of 4095 (depend on direction of movement)
  • By next shaft turn error is usually cleared
  • When I change direction of movement, index error sometimes appears again, sometimes not.
  • I noticed that QEPSTS[FIMF], which should be set when first index is received is NEVER set to 1.
• To make things more complicated, I have two CPUs connected to one source of QEP signal, but they are not acting the same. Sometimes firs one acting problematically, sometimes second one, sometimes both, sometimes both are OK.
  • Also sometimes, when I am spinning by shaft for example to the right, one of CPU detect transition of index signal by turning right, and second one detects transition to the left (QEPSTS[QDLF]).

At first, I used QDECCTL[QIDIRE] = 0

• Issue happened more often
• Difference was not just 1, but usually 2 or 3.
• QEPSTS[FIMF], which should be set when first index is received is sometimes set to 1, sometimes not, again one CPU have the flag set, one not and so on.

When I am looking on QEP signals on logic analyzer, timing of signals looks good.

So, please:

1. Do you see any problem in QEP configuration?
2. Can you please advise me what else I can do to make detection of the index signal working correctly?
3. Is there available any documentation of QDECCTL[QIDIRE] bit functionality? I did not found anything describing what it is good for, what it should solve, …