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[C6655] PLL locked in ROM Bootloader?

Naoki Kawada
Guru 19890 points

Hi,

Please take a look at C6655 data sheet.

2.5.3 PLL Boot Configuration Settings

In this table, the default setting of PLLD and PLLM registers seems to be defined by BOOTMODE pins, assuming "Input Clock Freq". These are 50.00/66.67/80.00/100.00/156.25/250.00/312.50/122.88 Mhz.

My understanding is that...
1. this table defines just default values of PLLD/PLLM assuming the above pre-defined input clock frequency and ROM Bootloader *never* configures PLL with them. Configuring MAIN PLL is user's option in IBL.
2. So, user can use another value for input clock freq if it meets the requirement described in 7.5.5 Main PLL Controller/SRIO/HyperLink/PCIe Clock Input Electrical Data/Timing, i.e., 3.2ns(min)/25ns(max)

Is my understanding correct ?

Best Regards,
Kawada

  • 0
    TI__Mastermind 42545 points

    Hi Kawada,
    The following is stated in section 2.2 of the KeyStone Architecture DSP Bootloader User's Guide.
    • The RBL configures the system PLL to set the device speed. The boot configuration pins provide the RBL with the information about the reference clock used in the system. RBL gets the optimal operating speed of the device from the e-fuse register. The various reference clock frequency and operating clock frequency lists are available in the device-specific data manual.
    • The main PLL stays in bypass mode for no-boot, SPI, and I2C boot. For other boot modes, a PLL initialization sequence executes inside the boot ROM to configure the main PLL in PLL mode.
    The RBL will determine the values needed to get the optimal speed based on the input clock frequency specified and the device limits specified in e-fuse and set up the PLL with those values. If you are using a frequency that is not specified in the list available for 'input clock frequency' boot configuration, you should choose a frequency from the list that is higher than the frequency of CORECLK. This will ensure that the PLL is not configured for a frequency that exceeds the capabilities of the C6655.
    Regards, Bill

  • 0 in reply to Bill Taboada
    Guru 19890 points
    Hi Bill,

    Thank you for your help. OK, I understood.

    Best Regards,
    Kawada