= Adventures in Bare Metal Programming on the Raspberry Pi

== Introduction

This code is is an example of working in bare metal on the Raspberry Pi.

== Requirements

1. Linux desktop (my instructions are Debian based)
2. Raspberry Pi
3. A 3.3v USB UART that supports linux, e.g. 
   http://www.amazon.com/gp/product/B006JKNWLE

== Instructions

=== The bootloader

First you need to install bootloader05 from
https://github.com/dwelch67/raspberrypi on your pi. Copy kernel.img
and make an empty config.txt file on your SD card. I presume you
already have one with the other stuff used by the pi to boot, e.g. I
had a berriboot SD card.

=== Bootstrap your Linux desktop for development

First add the following to /etc/apt/sources.list

  deb http://www.emdebian.org/debian/ squeeze main

Then execute

  sudo apt-get update

Next execute 

  sudo apt-get install rake
  rake bootstrap

This will install the GNU ARM C compiler.

=== Connect up your Serial UART

See this diagram https://sites.google.com/site/burngatehouse/home/drawings/GPIOs2.gif

I position the board so that the HDMI cable is on the left the serial
cables and Ethernet cable are on the bottom. When position so the set
of p1 connectors is on the top right of the board. It is labled on the
board p1 just to the top left of the connector. The UART lines 3
(GND), 4 (TX), 5 (RX) counting down from the top the right column from
starting with the first pin being pin 1. The pins on my serial UART
are also labled. Connect TX to RX and RX to TX and GND to GND. My
serial UART came with female to female connectors and so it was easy.

=== Build the bare metal program and load it

1. Execute 

  rake run

2. Apply power to your Raspberry pi. You should see a pattern on the
HDMI screen and some output from the serial program running from the
previous command.

You should see output like this:

  Sending /home/richcole/clients/github/RaspberryPi/build/kernel/kernel.bin, 3 blocks: Give your local XMODEM receive command now.
  Xmodem sectors/kbytes sent:   
  [snip]
  00000014 
  00000015 
  00000016 
  Bytes Sent:    512   BPS:125                             

  Transfer complete
  PIPE Signal 13
  Process terminated 0000017 
  00000018 
  00000019 
  0000001A 
  0000001B 
  0000001C 
  0000001D 
  11111111 
  22222222 
  333!

=== You're done

This is as far as I got so far. The lack of a power reset switch is
going to be painful as one has to unplug the power and plug it back in
again to reset the device. I'm hesitant to open up the the power cord
to install a switch. Instead I might find a power socket with a
switch, they don't seem to have power socket switches here in the US
like they do in Australia.

David Welch recommends the purchase of jtag adapter. 
  http://www.raspberrypi.org/phpBB3/viewtopic.php?f=72&t=19623 

Next steps are to make the bootloaded program do something more
interesting and to find more specs about what is where.

This document has some info:

  BCM2835-ARM-Peripherals.pdf

Here is a link to a nice blog about writing a OS for beagle boards

  http://www.embedded-bits.co.uk/category/beagleboard/

=== QEMU ===

  arm-linux-gnueabi-gdb --annotate=3 
  file build/kernel/kernel.qemu.elf
  target remote :1234