Videoray Bootloader

PREAMBLE:
On all AVR mcu based devices (PRO4, PAM, etc.) VideoRay uses a simple bootloader.  This bootloader allows for simple field upgrades of firmware and provides mechanisms for device serialization and data storage.

The bootloaded is based upon MegaLoad by Microsyl.  It communicates with a host via a serial connection, typically RS-485.

The bootloader is located in the bootreagion of the MCU FLASH.  Upon device reset the MCU will begin execution of the bootloader.  

The bootloader size is 1K words.





COMMUNICATION PROTOCOL:
The bootloader uses the following communication protocol, again based upon MegaLoad.

Protocol:
Target sends "$VRBL:"
Target sends the first 32 bytes of EEPROM (this is device id information, see below)
Target listens for a char until timeout.  Ignores it.
Target sends a '>'
Target listens for a '<' response
	if timeout then target jumps STARTAPP (see below).
Target receives 16 bytes, these must ether be all 0xAB or match the device serial number exactly.  
	If the device serial number is less than 16 bytes, the remainder should be 0x0.
	If the serial number does not match then the Target sends a '@' and jumps to STARTAPP (see below)
Target sends '*' to indicate Serial Number match 
Target sets Application Flag in eeprom to INVALID
Target sends 5 bytes: (bytes are codes for various values)
	PageSize
	DeviceID
	FLASHSIZE
	BOOTSIZE
	EEPROMSIZE
Target listens for a char until timeout.  Ignores it.
Target sends '!'
Target loops until it gets 0xffff for a page address
	Host sends 2 byte page number (NOTE: PAGE NUMBER 0,1,2... not an address) (MSB first)
	Host sends PageByte/2 16-bit words (64 words or 128 bytes for atmega128)
		words are sent LSB
	Host sends checksum checksum is mod 8 sum (just add usigned chars)
	Target sends '!' for ok page write or '@' for error.
Target sets Application Flag in eeprom to VALID if no errors.
STARTAPP:	
	Target checks that a valid application is stored.  This is determined by a "Valid Application" flag in EEPROM
	If the flag is set, then the bootloader will jump to to 0x0000.  otherwise it will perform a watchdog timeout 
	inorder to reset.





EEPROM DATA STRUCTURES (ATMEL AVR-128)
The bootloader assumes a standard usage of data structures in EEPROM.  The first 32 bytes are allocated for 
bootloader usage

Standard EEPROM MemoryMap:
EEPROM (4K separate Data Space)
0x0000 - 0x001f BootloaderID Data
  0000 -   0001 Bootoader Version	
  0002 -   0003 Device Type
  0004 -   0014 Serial Number	
  001C -   001F Valid App Flag (0x60 0x0D 0xF0 0x0D)
0x0020 - 0x03ff Hardware Config
0x0400 - 0x0ffA Application DATA
0x0ffc - 0x0fff Hardware Runtime


Bootoader Version:
This is the ordinal number of the bootloader version

Device Type:
This matches the standard videoray device type ID's

Serial Number:
This is a 16 byte ascii character string which represents the serial number.
Serial numbers are generally of the form *YYSSS:
where * is an arbitrary string designation,   YY is a two digit year code, and SSS is the sequence number.

Valid App Flag: 
This is used to mark a downloaded firmware app as valid.  If these locations equal 0xG00DF00D then 
the application is considered valid and the bootloader will jump to 0x0000 on startup (after bootloader sequence)

Hardware Config:
This is where model specific hardware data is stored.   Typically this is data such as individual part versions in a multi-part device, such as a PRO4 sub.

Application DATA:
This is were application firmware may store it's data.  The data and dataformats are specific to the individual application firmware.

Hardware Runtime:
If implemented, this is where the device runtime is stored.