raspberry pi 4 -- work in progress!

broadcom 2838 SoC (based on 2711)
4 x cortex-a72 (1500Mhz, out-of-order pipeline)

Needs firmware from 5 July 2019 or later.

config.txt for pi4 should include 'core_freq=250' for
the mini-uart console, and 'device_tree=' to ensure that
the loader passes an ATAG list to the kernel instead of
a device tree.

On a 4GB (or 2GB) pi4, a little less than 2GB will be
used.  (0x7D000000 bytes to be precise.)