Atmel AVR2054 User manual

Atmel AVR2054: Serial Bootloader User Guide
Features
• Description of serial bootloader
• Hardware configuration instructions
• Embedded bootloader description
• Instructions on how to use the Bootloader PC tool
• Creating SREC images
Introduction
The serial bootloader is a stand-alone package consisting of two parts: embedded
bootloader that should be loaded to the flash memory of a supported MCU and the
PC based application that sends data to the embedded bootloader over serial link.
The package contains all necessary sources for modifying and compiling the
embedded bootloader, including makefiles and projects files for various
development tool chains.
Chapter 1provides an overview of serial bootloader and package’s contents as
well as a brief starting instruction. Following chapters cover more specific topics.
Hardware configuration including ports and fuse settings is covered in Chapter 2.
Chapter 3describes embedded bootloader application and specifics of its different
kinds. Finally, Chapter 4gives instructions on how to create an SREC image and
program a device with it, using the Bootloader PC tool.
8-bit Atmel
Microcontrollers
Application Note
Rev. 8390B-AVR-12/11

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1 Overview
The serial bootloader allows loading of firmware images to devices from a PC
application over the serial connection. It is intended for use with Atmel®wireless
stacks, such as IEEE®802.15.4 MAC, RF4CE, BitCloud®and BitCloud Profile Suite,
but can also be used with non-wireless applications.
An application image is received and written to the flash by embedded bootloader,
which must be programmed to the devices beforehand. The package contains pre-
compiled images of the embedded bootloader application for a wide set of
configurations as well as its source code with projects files for different toolchains.
The embedded bootloader application can be built using Atmel AVR Studio®5, IAR
Embedded Workbench®, or the command line. To enable this, the package provides
AVR Studio 5 project files, IAR™ project files, and makefiles.
A firmware image should be in the Motorola S-record hexadecimal format (SREC)
and may be transferred to a device programmed with the embedded bootloader by a
special host application. The host may be a PC or another MCU and should be
connected to the device via a serial interface as shown in Figure 1-1.
The package provides the Bootloader PC tool for a PC to act as a bootloader host.
The tool comes as a GUI application and a command line tool and is used to load
firmware images through the serial connection to devices pre-programmed with the
embedded bootloader.
Figure 1-1. General approach for using bootloader to program a device.
The Bootloader PC tool may also be used to initiate an Over-the-Air upgrade (OTAU)
of a ZigBee®network by transferring a firmware image to the OTAU server device
connected to the PC via a serial interface. See [3] for more detail.
1.1 Supported platforms
Embedded bootloader is supported on a set of Atmel microcontrollers and
development boards shown in Table 1-1. Note that embedded bootloader can work
with different serial interfaces. Supported serial interfaces are specified in the
Makefile of the embedded bootloader application at compile time (see Section 2.1).

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Table 1-1. Supported MCUs and corresponding boards and modules.
MCU (Atmel) Supported modules (Atmel) Development board/kit
ATmega1281
ATmega2561
ATZB-24-B0
ATZB-24-A2
ATZB-A24-UFL
ATZB-900-B0
MeshBean,
RCB230/231/212 (1)
ATmega128RFA1 N/A
ATRF4CE-EK (RCB128RFA1
mounted on RCB Key Remote
Control board, RCB Sensor
Terminal Board or
RCB-BB),
ATAVR128RFA1-EK1
ATxmega256A3
ATxmega256D3 N/A
Atmel STK®600,
REB2xxED-EK
AT91SAM3S4C N/A deRFusb-23E00 (1)
Notes: 1. These are not Atmel products; see http://www.dresden-elektronik.de for
purchase.
1.2 Contents and structure
The package contains
•Embedded bootloader sources, including
oSource code and header files
oMakefiles for various configurations
oIAR projects (though not present for the bootloader for RF4CE
applications)
oAtmel AVR Studio 5 projects
•Pre-compiled firmware images of embedded bootloader
•Installation files for the Bootloader PC tool
•Documentation
Table 1-2 describes the serial bootloader file structure with paths given in regard to
the package’s root directory.
Table 1-2. Serial bootloader files and directories.
Path Description
\Embedded_Bootloader_images\
Pre-compiled firmware images of
embedded bootloader
\Embedded_Bootloader_src\ Embedded bootloader sources
\Embedded_Bootloader_src\application\
Embedded bootloader source
code
\Embedded_Bootloader_src\ iar_projects\
IAR Embedded Workbench
project files for embedded
bootloader. Project files for
RF4CE version are not provided.
\Embedded_Bootloader_src\bootloader.aps
Atmel AVR Studio 4 project file for
the embedded bootloader

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Path Description
\Embedded_Bootloader_src\as5_projects\
Atmel AVR Studio 5 project and
solution files for the embedded
bootloader
\Embedded_Bootloader_src\makefiles\
Makefiles for compiling the
embedded bootloader with IAR or
GCC compiler from the command
line or from AVR Studio 4 and 5
\PC_Bootloader_Setup\
Installation files for the Bootloader
PC tool
\Documentation\ Documentation folder
NOTE There are three types of embedded bootloader firmware distinguished by their
functionality: common bootloader, the bootloader with OTAU support for Atmel
BitCloud applications, and the bootloader for RF4CE applications. The latter two
provide extra functionality in addition to common bootloader features. For details see
sections 3.5 and 3.6.
1.3 Getting started
Serial bootloader is typically used in the following way:
1. Unpack the package to a folder on the PC hard drive.
2. Install the Bootloader PC tool. To launch the Bootloader PC tool you will need to
install Java®, if it is not installed on your PC.
3. Program the target device with an image of the embedded bootloader via JTAG,
unless it is already programmed.
4. Configure fuse bits for the bootloader support (see Section 2.2) if needed.
5. Connect the device via the serial interface to the PC.
6. Launch the Bootloader PC tool, specify the connection settings, the application
image in SREC format, and upload the image to the target device (see Section 4.1
for the detailed instruction).
2 Hardware configuration
Bootloader support may require changes in hardware configuration as described
below.
•Consider proper configuration of the serial interface that will be used to transfer a
firmware image from a PC to the device. Embedded bootloader and the Bootloader
PC tool can work with USART, SPI and USB, although the set of supported
interfaces depends on a platform
•Check fuse bits settings (Atmel AVR®and XMEGA®MCUs). An MCU must be
aware of the size of the memory occupied by the bootloader if it resides in the flash
and must start from the bootloader section rather than from the application section.
Section 2.2 describes fuses configuration for AVR and XMEGA highlighting the
differences where necessary

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2.1 Serial interface
Table 2-1 describes default serial interfaces used by the embedded bootloader to
upload firmware images. The interface settings may be changed in the
configuration.h file of the embedded bootloader application (see Section 3.3).
Table 2-1. Default serial port settings for embedded bootloader.
Platform (Atmel) Default port Comment
ATxmega256A3/D3 on
STK600 and REB-CBB
(REB2xxED-EK) USART0 on port D
For STK600, connect RXD/TXD
connectors with PD2/PD3 pins,
connect to PC via RS232
ATmega128RFA1 on
STK600 USART1
Connect RXD/TXD connectors with
PD2/PD3 pins, connect to PC via
RS232
ATmega128RFA1 on Red
Key Remote Control Board
(ATRF4CE-EK) USART0
ATmega128RFA1 on
Sensor Terminal Board
(ATRF4CE-EK) USB_FIFO
ATmega128RFA1 on
RCB-BB(ATRF4CE-EK) USART1
ATmega1281/2561
(MeshBean) USART1
For MeshBean and RCB attached to
an expander board, connect the
board to a PC via the USB port
AT91SAM3S4C
(deRFusb-23E00) USB DFU
For USB sticks, attach the device to
the USB port on a PC
2.2 Fuse bits settings
NOTE This section does not consider SAM3S, since this MCU does not have fuse bits.
Embedded bootloader firmware (if not yet loaded to a device) shall be uploaded over
the JTAG or ISP interface. Fuse bits must be configured correctly.
Recommended fuse bits for supported AVR microcontrollers are given in Table 2-2,
and fuse bits for supported XMEGA microcontrollers are given in Table 2-3. The
tables enumerate all fuse bits and show the resulting fuse bytes.
Table 2-2. Fuse bits on ATmega1281 and ATmega128RFA1.
Option
Common
bootloader
OTAU bootloader for Atmel
BitCloud applications
Bootloader for RF4CE
applications
BODLEVEL Disabled Disabled
Brown-out detection at
VCC = 1.8V
OCDEN Disabled Disabled Disabled
JTAGEN Enabled Enabled Enabled
SPIEN Enabled Enabled Enabled
WDTON Disabled Disabled Disabled
EESAVE Disabled Disabled Enabled

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Option
Common
bootloader
OTAU bootloader for Atmel
BitCloud applications
Bootloader for RF4CE
applications
BOOTSZ
Boot Flash
size=1024
words start
address=$F
C00
Boot Flash size=2048 words
start address=$F800
Boot Flash size=2048
words start address=$F800
BOOTRST Enabled Enabled Enabled
CKDIV8 Enabled Enabled Enabled
CKOUT Disabled Disabled Disabled
SUT_CKSE
L
Int. RC osc.;
Start-up
time: 6 CK +
65ms
Int. RC osc.; Start-up time: 6
CK + 65ms
Int. RC osc.; Start-up time:
6 CK + 0ms
Resulting
bytes
0xFF 0x9C
0x62 0xFF 0x9A 0x62 0xFE 0x92 0x42
Fuse bits configuration informs the MCU to start execution from the bootloader
section in memory instead of the application’s. On Atmel AVR microcontrollers the
bootloader is stored in the flash memory in the same address space as the
application. This reduces the amount of memory available for the application. The
fuse bits are also used to specify the amount of memory exclusively reserved for the
bootloader. Bootloader size may also vary depending on the bootloader type (for
example, the OTAU bootloader requires larger memory allocation than a bootloader
without OTAU support).
On XMEGAs, the embedded bootloader is kept in a separate storage, and so it is not
needed to specify the size of the bootloader section (all 256kb of flash are available
as the application memory).
Table 2-3. Fuse bits on Atmel ATxmega256A3 and Atmel ATxmega256D3.
Option Required value
JTAGUSERID 0xFF
WDWP 8 cycles (8ms @ 3.3V)
WDP 8 cycles (8ms @ 3.3V)
DVSDON OFF
BOOTRST BOOTLDR
BODACT Disabled
BODPD Disabled
SUT 0ms
WDLOCK OFF
JTAGEN ON
EESAVE OFF
BODLVL 1.6V
Resulting bytes
FUSEBYTE0 0xFF
FUSEBYTE1 0x00

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Option Required value
FUSEBYTE2 0xBF
FUSEBYTE4 0xFE
FUSEBYTE5 0xFF
3 Embedded bootloader
Embedded bootloader occupies a little amount of memory and serves the only
purpose, to load an application image from a serial interface and write it to the MCU’s
internal flash and/or EEPROM. A simple communication protocol is used to ensure
proper programming. Figure 3-1 illustrates bootloader organization.
The embedded bootloader application is provided as a set of pre-compiled firmware
images for various configurations and the source code. The user can immediately
start using boot loading by programming devices with the pre-compiled images. It is
also possible to modify the source code of the embedded bootstrap and compile it
using the appropriate toolchain.
Figure 3-1. Embedded bootloader architecture.
In addition to the common bootloader that simply programs application firmware to
the flash and EEPROM, embedded bootloader application may be built to support
additional features like Over-the-Air upgrade applied by BitCloud applications or
RF4CE features. The OTAU bootloader is able to load an application image, which
has been received by the application over the air and saved in an external memory
device, and program it into the internal flash memory (see Section 3.5). RF4CE
features are invoked by the application to enable a special type of the Over-the-Air
upgrade when the application image is replaced in memory simultaneously with
reception of the new image. For detail refer to Section 3.6.
3.1 Bootloader UART/SPI programming sequence
The embedded bootloader may process data received in the SREC format, using the
following algorithm:
1. After the device is reset, the embedded bootloader waits 200ms for each
configured interface for a HANDSHAKE_REQ data sequence to arrive via the
serial interface. If no HANDSHAKE_REQ is received, the embedded bootloader
jumps to the application’s entry point in the flash memory.
2. If a HANDSHAKE_REQ sequence is received, bootstrap code sends a
HANDSHAKE_CONF sequence over the serial interface and starts receiving
SREC records one by one.

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3. For every valid SREC record the embedded bootloader responds with an ACK
data sequence over the serial interface.
4. In case of any error during loading process, the embedded bootloader sends a
NACK data sequence, then proceeds to (1).
On the PC side, the Bootloader PC tool performs the following actions:
1. The Bootloader PC tool sends a HANDSHAKE_REQ data sequence for 30
seconds with 200ms interval, waiting for a HANDSHAKE_CONF data sequence
between transmissions. Any reply except HANDSHAKE_CONF is ignored.
2. If HANDSHAKE_CONF is received, the PC bootloader starts sending data from
the SREC file via the serial link. Each record of the SREC file is converted to
binary representation before sending.
3. For every record sent the host expects an ACK over the serial link as a response.
If a NACK sequence is received or a timeout occurs, the PC bootloader aborts.
Serial data sequences used between the device and the host while boot loading:
•HANDSHAKE_REQ: 0xB2, 0xA5, 0x65, 0x4B
•HANDSHAKE_CONF: 0x69, 0xD3, 0xD2, 0x26
•ACK: 0x4D, 0x5A, 0x9A, 0xB4
•NACK: 0x2D, 0x59, 0x5A, 0xB2
Figure 3-2 illustrates the flowchart of the serial bootloader programming algorithm.

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Figure 3-2. Serial bootloader programming algorithm.
3.2 Bootloader USB DFU specifics
The embedded bootloader for Atmel SAM3S microcontrollers operates in a different
way than shown in Figure 3-2 to conform to certain features of the SAM3S
microcontroller and development boards, on which it is hosted.
Embedded bootloader for SAM3S uses Device Firmware Upgrade (DFU) standard. A
DFU component should be included in the application (see Section 3.2.2.1). The
procedure of uploading a new firmware image does not change for the user. For
detailed instruction see Section 4.1.2. The remaining part of this section describes
implementation details of SAM3S embedded bootloader and is intended for users
who will possibly modify the embedded bootloader code.

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3.2.1 Changing the reset vector
The Atmel SAM3S MCU does not contain a special bootloader section in the flash
memory1. The fuse settings do not indicate whether to start execution from the
application section or from the bootloader section and where this section starts. So if
the bootloader code is first programmed at the end of the flash memory and then the
application code is loaded into the remaining part of the flash memory, the MCU will
start code execution from the last loaded code after reset (that is, the application
code).
In order for the embedded bootloader to work correctly it must receive control first
after reset to be able to communicate with the host software and upload a new device
image before the application code is executed.
To achieve this, the embedded bootloader for SAM3S, during uploading, reassigns
the reset vector value (the MCU component that stores the address to start from
reset), setting it to its own starting address. Thus the MCU will always start execution
from the embedded bootloader, which, in turn, will pass control to the application
section upon completion.
3.2.2 DFU impact
Another feature involves notifying embedded bootloader that the PC tool is ready to
transfer a new firmware image to the device. For the Atmel AVR and XMEGA MCUs
the device must be reset before the new software upload can take place. Upon reset
the COM port assigned to the device on the PC is still enabled. The bootloader
receives control and waits for the uploading requests from the PC tool. However, to
reset a USB stick with SAM3S it should be removed and re-attached to the PC. This
may cause the PC to assign a different COM port to the device and stop the serial
communication with the device.
To prevent serial port reassignment when using SAM3S, the USB Device Firmware
Upgrade components based on [5] should be used. DFU components should be
included in both the embedded bootloader and the application code (see Section
3.2.1). The DFU component inserted in the application code should always be
enabled along with other application components. Upon receiving a command
indicating that a new firmware image is ready, it writes a special byte into the program
memory and initiates a device reset. After reset, the DFU component included in the
embedded bootloader checks this status byte and enters the new firmware upload
mode.
If the embedded bootloader is the only image loaded in the program memory, it will
constantly be ready to receive and upload a new firmware image from the host.
3.2.2.1 Adding DFU support to an application
The DFU class for the application is implemented on top of the USB driver. Set the
DFU_SUPPORT parameter to 1 in configuration.h file to enable DFU support:
#define DFU_SUPPORT 1
3.2.2.2 Not-responding application or absent DFU
The application loaded to the flash by embedded bootloader may not include a DFU
component as well as any special code to deal with PC tool’s requests. In other cases
1A dedicated bootloader ROM section is included by individual manufactures for their
individual use.