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How to running Image in the SDRAM

The following high-level overview lists the tasks that the boot loader performs in a semi-chronological order, immediately following a CPU reset:

  • Early CPU initialization.
    • Enter supervisor mode.
    • Clear the instruction and data caches.
    • Clear the translation look-aside buffers (TLBs).
    • Drain the write and fill buffers.
    • Configure and enable the RAM controller.
    • Ensure that interrupts are cleared and masked.
    • Initialize any required phase-locked loops (PLLs) or timebases such as RTC and tick counter.
  • Optionally relocate the run-time image to RAM. The boot loader may initially run in flash memory after reset.
  • Optionally enable the MMU and caches
  • Copy the copy-section data to its final location. This instantiates initialized global data.
  • Create and populate a reserved memory area to be shared with the OS. This boot arguments or boot args area is used to pass along various bits of information to the OS.
  • Early board-level initialization.
  1. Set up debug UART.
  2. Optionally provide a user menu for configuring loader options.
  3. Initialize the Ethernet controller.
  • Optionally obtain an IP address for the target from a DHCP server. An alternative would be to assign a static IP address to the device.
  • Initialize the TFTP connection. Platform Builder uses the TFTP protocol to download .bin files from the development workstation.
  • Download the .bin file as individual records, then verify each with a checksum, and then store the data where each record indicates it needs to be stored. The operation is slightly different if the run-time image is to be stored in flash memory.
  • Obtain various user settings from Platform Builder, such as boot clean and whether to establish a passive KITL connection, as well as IP and port address information for various Platform Builder service connections.
  • Execute the downloaded .bin file by ensuring the system state is configured appropriately and then jumping to the run-time image's startup address.
 
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