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HPI Ready Problem with TMS320C6455

Ilkay Sebnem Kadioglu
Prodigy 60 points
Other Parts Discussed in Thread: TMS320C6455

Dear Sir/Madam,

We produce own boards which have on 6455 DSPs.

My question is about HPI protocol. In spru969b.pdf (TMS320C645x DSP Host Port Interface User's Guide) document, HRDY bit in Control Register (HPIC) can be used for understanding HPI is ready. On the other hand in TMS320C6455 datasheet, "Software handshaking via the HRDY bit of the Host Port Control Register (HPIC) is not supported on the C6455 device". So, we should not use HRDY bit if the HPIC register, and we should trust external HRDY signal for understanding HPI is ready; shouldn't we?

There are some cases about that question:

When we access DSP via HPI,

(first case) HRDY signal is only used for understanding HPI is ready or not, but the reading data is corrupted.

(second case) HRDY signal and HRDY bit of HPIC are used for understanding HPI is ready or not, and the reading data is fine  (we set fetch bit before reading HRDY bit of HPIC)

For first case, we do not operate HPI protocol.

For second case,  it seems that we can operate HPI protocol properly but we encounter rarely a problem that read data is not fine even if HRDY signal and HRDY bit of HPIC are ready.

Can you help us about these question:

  1. Is controlling HRDY signal enough for decision HPI is ready or not for 6455? If answer is “Yes”, why we might be encountering problems (first case)?
  2.  When we set fetch bit of HPIC, what may be changing?

Ilkay

  • 0
    TI__Mastermind 35645 points

    Hi llkay,

    Thanks for your post.

    Basically, the HPI was designed to use the HRDY pin, but in some cases, if the host does not have an input pin to connect to the HRDY pin, the host can check the readiness of the HPI by polling the HRDY bit in the control register (HPIC)

    Actually, accessing fetch bit of HPIC will be applicable only when the host does not have an input pin to connect to the HRDY pin. if this is the case, the host reads the status of HRDY bit of HPIC through software polling. Again, if fetch bit of HPIC is set, the FETCH command and autoincrement HPID read cycles may perform reads in this mode while using HRDY polling.

    To know more details, please walkthrough hardware handshaking using HRDY signal (Section 3.9) and software handshaking using HRDY bit (Section 4) in the C645x HPI user guide as shown below:

    http://www.ti.com/lit/ug/spru969b/spru969b.pdf

    Thanks & regards,

    Sivaraj K

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  • 0 in reply to Sivaraj Kuppuraj
    Prodigy 60 points

    Hi Sivaraj,


    Thank you for your answer.

    I had read http://www.ti.com/lit/ug/spru969b/spru969b.pdf. On own board is possible to measure HRDY signal, and datasheet of 6455 DSP is saying "Software handshaking via the HRDY bit of the Host Port Control Register (HPIC) is not supported on the C6455 device".

     

    Can you help me about that question:

    If we follow only HRDY signal, we can not read reliable data from DSP. If we follow together HRDY signal and HRDY bit of HPIC -despite 6455 DSP does not support HRDY bit of HPIC -, we can read realiable data from DSP. How can it be possible?


    Best regards,

    Ilkay

  • 0 in reply to Ilkay Sebnem Kadioglu
    Prodigy 60 points

    Hi,

    I wrote that message for reminder.

    Ilkay