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1. Initial instruction

• Execution after reset starts at 0xfffffffc
  • A branch instruction (either b or ba; 26 bit ramge) to some boot code is loaded here
    • The Xilinx example branches to in block RAM (bram) at 0xffffff00
    • The RTEMS example branches to download_entry (but I'm not sure how)
  • Potentially a sc (system call) instruction could be loaded here? Any advantage to this?
    • Probably not as the corresponding ivor register (PPC 440) is not loaded yet
    • The PPC 405 doesn't have ivor registers, so it would continue executing at the system call vector

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1. dlEntry.s

   This is written for the PPC 440 found in Xilinx Virtex 5 parts.

• In our case, the boot code starts at startup
  • Other names are start, download_entry and __rtems_entry_point
• Boot code vaguely follows the "Initialization Software Requirements" outlined in the PowerPPC 440x5 Embedded Processor Core User's Manual v7.1 from IBM
  • Why only "vaguely"?
• Clear MSR
• Disable debug events
• Configure instruction and data cache registers
• Set up decrementer and timer registers
• Clear exception registers ECR and XER
• Invalidate instruction and data caches
• Clear the CPU reservation bit
• Set up CCR0, CCR1, MMUCR, CRF and CTR
• Set up TLB pages
• Set up debug events
• Set up EABI and SYSV environment
• Clear out BSS section
• Load vector offset register
• Set up TOC ( r2 overwritten?)
• Set up initial stack
• Set up argument registers r3, r4 and r5
• Branch to boot_card()

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1. boot_card()

• Command line is in first argument
• Disable interrupts
• Store command line
• Call bsp_start()
• Determine RTEMS work area and heap
• Initialize RTEMS data structures
• Initialize the C library
• Call bsp_pretasking_hook()
• Optional: Enable RTEMS debugging capabilities
• RTEMS initialization before loading device drivers
• Call bsp_predriver_hook()
• Initialize device drivers
• Call bsp_postdriver_hook()
• Start multitasking
  • Thread with entry point Init runs
  • Not clear how this returns. Perhaps when the last task is deleted?
• Call bsp_cleanup()
• Return to start code
  • Not clear what's in the lr at this point, i.e., where do we return to?

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1. RTEMS BSP

• bsp_start()
• bsp_pretasking_hook()
• bsp_predriver_hook()
• bsp_postdriver_hook()
• bsp_cleanup()