Application images in flash:

In order for the nCS0 flash content to be considered a valid bootable image
(i.e., for the boot ROM to transfer control to it, rather than wait forever
for a UART download), the 32-bit word at address 0x2000 (the first word
after the ROM-overlaid portion) must contain either 0 or 1, corresponding
to two supported environment options:

* If the word at 0x2000 equals 0, it signifies an application image that is
  designed to run with the boot ROM still mapped at 0, with ARM exceptions
  vectoring through the 7 magic RAM locations at 0x80001C, and possibly
  through the 2nd level ("user-friendly") vector table at 0x800000 as well.

  If the word at 0x2000 equals 0, the following word at 0x2004 must contain
  the absolute address of the boot entry point; the boot ROM will transfer
  control to that address with the FFFF:FB10 register set to explicitly map
  the internal boot ROM at 0.  It is a BX-style address: setting the least
  significant bit will result in control being transferred in the Thumb state.

* If the word at 0x2000 equals 1, it signifies an application image that is
  at least conceptually independent of the Calypso boot ROM - one that would,
  at least in theory, function correctly with nIBOOT tied/pulled/driven HIGH,
  or even on an older DBB chip with no internal boot ROM.

  When the boot ROM code sees a 1 in the 0x2000 word, it copies a little piece
  of code into the internal ROM and runs it there; this code sets the FFFF:FB10
  register to disable the internal boot ROM (map the external nCS0 memory at 0,
  as if nIBOOT were high) and causes the watchdog timer to go off, resetting
  the ARM core and causing it to execute the external nCS0 reset vector.

RAM layout:

800000 7 words:
	soft-vector pointers: by default the following 7 words at
	80001C are filled with ldr-jump instructions, which read
	from these 7 words and load them into PC
80001C 7 words:
	hard vectors: the physical vector locations in the ROM
	contain branch instructions to these 7 RAM addresses
800038:	The helper routine for transferring control to type 1 flash images
	is copied to and run here.
800100:	the last word of the above routine
800104: word initialized to 0x0001D4C0
800108: byte initialized to 0x01

800520: byte variable filled every time the 0xfb4 routine is called
	holds the ID of the UART on which '<' came in, or FF if none
800524: byte variable filled every time the 0xfb4 routine is called
	filled with a copy of 800534

800534: byte initialized to 0x00, then may be set to 1 by the 0xfb4
	routine if it selects /1 clock mode.

8005C0: appears to be the intended low address (bottom) of the stack
80074C: top of the stack (initial value loaded into SP)