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66AK2G02: Secondary boot using UART

Bob Walker
Prodigy 30 points
Part Number: 66AK2G02


Since DEVSTAT is set on the rising edge of reset and only affects the primary boot source, how does one select a particular UART to boot during the secondary bootloader phase?

  • 0
    TI__Guru**** 161600 points
    Hi,

    Uart boot is explained in 66AK2G02 TRM. See Section 4.3.2.12 UART Boot Device Configuration in the manual. You can see that the port from which the device will boot is selected with Boot pins [10:9]PORT:
    PORT Port select:
    • 0 = Boot on UART 0
    • 1 = Boot on UART 1
    • 2 = Boot on UART 2
    • 3 = Boot on UART 0

    Best Regards,
    Yordan
  • 0 in reply to Yordan Kovachev
    TI__Guru**** 161600 points
    You can see that for each primary boot mode, you have a backup, that is defined with pins [15:14].

    Best Regards,
    Yordan
  • 0 in reply to Yordan Kovachev
    Prodigy 30 points
    The backup field only specifies the device to use. For example, QSPI specifies the a backup boot with either USB or UART. The question is WHICH USB or UART? The boot flow diagram in figure 4.3.1 shows that the boot re-entry is AFTER the DEVSTAT update, which means that the config data for the UART is not available. It appears that this flowchart needs more detail. What is the mechanism that selects UART0, UART1, UARTn? How is that set and does the secondary (backup) boot option update the DEVSTAT register?
  • 0 in reply to Bob Walker
    TI__Guru** 116770 points
    Bob,

    I agree with your assessment, we need to add the information regarding specific instances of these peripherals that will get used when the bootROM goes to the backup boot mode and I will file a litbug so that this can be addressed. In the meantime, I looked at the bootROM source to see which instance is used and it appears the Min default setup is used to setup back up peripheral which means UART Instance 0 and USB0 is used for backup boot. Min Default values also absent in the BOOTMODE section but can be found by looking at the default values in the boot parameter table in section 4.3.3

    The bootROM will not update the DEVSTAT when it goes to backup boot option.

    Regards,
    Rahul
  • 0 in reply to Rahul Prabhu
    Prodigy 30 points
    Thanks Rahul. That was the answer I was looking for.