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TMS320C5517: Boot Pin configuration after boot up

Kaka
Guru 24520 points
Part Number: TMS320C5517

Hi TI Experts,

Please let me confirm the following question.
[Question]
Can customer use the boot pins(EM_A[20:15]/GP[26:21]) as Output Pins after boot up?

My customer said that their custom board(it is used the C5517) could not control the boot pins GPIO[26;21] even though EBSR and IODIR was set as below.
EBSR: 0x193F
IODIR2: 0xFFFC

If you have any question, please let me know.
Best regards.
Kaka

  • 0
    TI__Guru**** 161600 points
    Hi,

    I've notified the team. Feedback will be posted here.

    Best Regards,
    Yordan
  • 0
    TI__Mastermind 29810 points
    Kaka-san,

    Yes, the C5517 can control the boot mode pins as GPIO[26:21] after reset. I confirmed it with the C5517 EVM, and in doing so I encountered two possible reasons for the customer's difficulty.

    First is voltage. On the C5517 EVM, DVDDIO2 (DVDDEMIF) is supplied with 1.8V and it cannot be changed on the EVM due to the IO range of the flash memories on the EVM (the C5517 processor can accept 1.8V or 3.3V). The DVDDIO1 voltage on the EVM can be changed to either 1.8V or 3.3V. so if the customer copied the C5517 EVM, they might be expecting 3.3V when driving a '1' through the GPIO instead of 1.8V.

    Second is contention. On the C5517 EVM, there is a level shifting transceiver U13 that always drives out by default. I had to force its OEn pin high in order to prevent contention when the C5517 GP[26:21] pins were also driving high.

    I used the same EBSR and IODIR2 register values you provided, which are correctly set to output the GPIO data. Are they controlling GP[26-21] with the IODATAOUT2 register (1C0Bh@IO)?
    I used a scope probe to measure the voltage on the GPIO pin while toggling IOOUTDATA2. Before forcing OEn on U13 high, the voltage only changed from 0V to ~300mV, indicating contention with another driver.

    We can find out what is going on with the answers to these questions...
    * Is DVDDEMIF the same voltage as DVDDIO (usually 3.3V or 1.8V)? Perhaps the GPIO is changing states, but 1 = 1.8V when 3.3V is expected.
    * What is the behavior of the GPIO pins when being driven by the C5517 GPIO register?
    * Does the measured voltage change at all when being driven by the C5517? This could reveal contention on the pins.
    * Are the pins all stuck low, high, or in the bootmode state?
    * How are the boot mode pins driven? Are they pulled high or low with resistors to GND and VDD?
    * What resistor value is used? They must not be shorted to GND and VDD or the GPIO cannot drive against the short. If they are driven by another device like MCU or IO expander, then the IO on the MCU or IO expander must go Hi-Z (input) to avoid contention on the bus.
    * Can they use CCS register view or memory window with the custom board to toggle the GPIO register bits? This requires JTAG on custom board.

    Hope this helps,
    Mark