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

2 Atmel AVR2054

8390B-AVR-12/11

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).

Atmel AVR2054

8390B-AVR-12/11

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

Atmel AVR2054

8390B-AVR-12/11

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

6 Atmel AVR2054

8390B-AVR-12/11

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

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

Atmel AVR2054

8390B-AVR-12/11

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.

8 Atmel AVR2054

8390B-AVR-12/11

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.

Atmel AVR2054

8390B-AVR-12/11

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.

10 Atmel AVR2054

8390B-AVR-12/11

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.

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