Command List:
=============

'i'  ... identify
'b'  ... boot
'r'  ... reset
'f'  ... read flash
'F'  ... write flash
'e'  ... read eeprom
'E'  ... write eeprom
'c'  ... read config
'C'  ... write config


Description:
------------

Every command consits of one byte command code, a fixed number of bytes as
arguments and ends with a XOR checksum over all bytes sent. All data is
transferred LSB first.
If the command code is unkown the bootloaders retunrns '??'

identify:
~~~~~~~~~
  command:
    'i' | <csum> (in this case <csum> will always be 'i')

  answer:
    'i' | version | name | fss | supported | <csum>

      version:
         2bytes, protocol version
         It is an error if the major version (MSB) is different (hence any
         protocol update must change the major version of the bootloader).

      name:
         10bytes, a descriptive name of the device.
         The downloader has to compare this name with the device name supplied
         via commandline and stop in case they don't match

      fss:
         1byte, flash segment size
         The number of words of one flash segment which has to be written at once.
         The downloader can fill up holes by supplying the illegal code word 0xFFFF
         for some addresses. The bootloader will skip those areas.

      supported:
         1byte, a bitmap showing supported commands
         The commands 'identify' and 'boot' are always supported by the bootloader,
         others may not (i.e.: not all PICs allow to update the configurtion words)

           bit | command
          -----+----------
            0  | reset
            1  | read flash
            2  | write flash
            3  | read eeprom
            4  | write eeprom
            5  | read config
            6  | write config


boot:
~~~~~

  command:
    'b' | <csum> (in this case <csum> will always be 'b')

  answer:
    'b' | <csum>


  This instucts the bootloader to boot to the user application directly (no reset)


reset:
~~~~~~

  command:
    'r' | <csum> (in this case <csum> will always be 'r')

  answer:
    'r' | <csum>


  The device performs a reboot. If the boot condition (i.e.: port pin) is not met
  this instructs the device to boot to the user application.


read flash:
~~~~~~~~~~~

  command:
    f | addr | <csum>

  answer:
    f | data | <csum>

  The bootloader reads <fss> words from flash address <addr> and returns it as
  <data>.


write flash:
~~~~~~~~~~~~

  command:
    F | addr | data | <csum>

  answer:
    F | (0|1) | <csum>

  The bootloader writes <data> (which has to contain exactly <fss> words) to address
  <addr> inside the flash. In case of Error '0' is returned, on success the return
  code contains '1'.


read eeprom:
~~~~~~~~~~~~

  command:
    e | addr | len | <csum>

  answer:
    e | data | <csum>

  The bootloader reads <len> bytes from eeprom at address <addr> and returns it as
  <data>.


write eeprom:
~~~~~~~~~~~~~

  command:
    E | addr | len | data | <csum>

  answer:
    E | (0|1) | <csum>

  The bootloader writes <data> (which has to contain exactly <len> bytes) to address
  <addr> inside the eeprom. In case of Error '0' is returned, on success the return
  code contains '1'.


read config:
~~~~~~~~~~~~

   command:
      c | nr | <csum>

   answer:
      c | word | <csum>

   The bootloader reads and returns the configuration word number <nr>.


write config:
~~~~~~~~~~~~~

   command:
      C | nr | word | <csum>

   answer:
      C | (0|1) | <csum>

   The bootloader writes <word> onto configuration word number <nr>. In case
   of an error '0' is returned, on success the return code contains '1'.