ATMega USB Bootloader
Short description
This project is a software USB Bootloader for Atmel© ATMega µControllers. It is based on
a software USB project v-usb .
This project includes build-scripts that are optimized for Windows Visual Studio nmake utility,
you will have to modify the makefiles, if you intend to use another make-utility.
The Bootloader requires some definitions from the main project, such as the clock speed and the
µController, that means the bootloader is not a standalone project, but it is intended to
be included in another project, which will create the main application, and the bootloader.
The BootLoader is compatible with 'Usb Bootloader' in FirmwareUI, use FirmwareUI to
communicate with this boot loader.
I have tested this bootloader with ATMega328p and with ATMega1284p devices, all running
with a 12MHz crystal. The software USB also supports CPU frequencies 12.8 MHz, 15MHz, 16MHz,
16.5MHz, 18MHz and 20MHz, however the 18MHz version might need some modifications in
avr/BootLoader/usbconfig.h, may have to set USB_CFG_CHECK_CRC = 1.
Please also read the data sheet for the specific µController, some devices
specify lower clock speeds when operated at power less than 5 V.
A sample project using the bootloader can be found in 'ATMega Tutorial 1' and
'ATMega Tutorial 2' on this web site.
Note The compiled size of the USB Bootloader is about 3 KBytes, that means the
target device must support bootloader with 4 KBytes or more (ATMega members with 32 KBytes Flash
and more allow for 4 KBytes bootloader size), in other words you cannot use this bootloader
with ATMega 8 or ATMega16 devices.
Directory Structure
I save all my µController projects in a base-folder, e. g. avr-development; Unpack the
contents of the zip file into the base-folder, which will result in the subfolders
- BASE_FOLDER
- BASE_FOLDER\avr
- BASE_FOLDER\avr\BootLoader
- BASE_FOLDER\avr\SoftUsb
BASE_FOLDER\avr\BootLoader contains the specific files for the USB Bootloader, BASE_FOLDER\avr\SoftUsb
contains all the files to build the software USB device from obdev, v-usb .
The application project should be located in a subfolder under BASE_FOLDER, e. g. BASE_FOLDER\MyApplication.
The buildfile will be executed from BASE_FOLDER, e. g. nmake -f MyApplication\makefile, which should
call nmake -f ./avr/BootLoader/UsbBootLoader.mak with all required parameters, see list below.
Build Parameters
The main buildfile must pass some parameters to the BootLoader build scripts. These Parameters are required:
- MCU: controller, e. g. atmega328p
- F_CPU: clock frequency of the cpu, required, in HZ, e. g. F_CPU=12000000 (12 MHz)
- TARGET: target directory, optional, defaults to ./temp/avr/BootLoader, the BootLoader will be built
in $(TARGET)\UsbBootLoader_$(MCU).elf
- USBCONFIG: directory for file usbbootconfig.h
- BUILD_OPTIONS: optional, any further options that might be used during build,
e. g. -DBOOTRST=1 (Reset vector jumps to boot section), the BootLoader will jump to the
application if no USB command is received within a few seconds
- MAKEFILE_DEP: optional, space separated list of dependency files, force rebuild if one of these
files is newer than the last build
The file usbbootconfig.h should reside in the application folder, it defines the hardware pin
assignement for the USB socket. There is s sample file defusbbootconfig.h in the BootLoader-folder
which describes the settings.
Communication Protocol
This bootloader implements a HID device using public vendor and product id's, VID = 0x16c0, PID = 0xdf05.
The vendor name is "www.loewenwasser.de", and the Device name is "CUsbBootLdr".
The HID report descriptor defines two Report IDs, Report 1 has a length of 16 Bytes, Report 2
has a length of 34 Bytes.
Report 1 read:
- Byte 0: always 3, Status, bit0: OK, Bit1: in Bootloader
- Byte 1: Interface Version, currently 1
- Byte 2 - 4: Device Signature, e.g. ATMega 1284p: 0x1e 0x97 0x05
- Byte 5, 6: Flash Page size, e. g. ATMega 1284p: 0x0100 (256 bytes)
- Byte 7, 8: Flash Pages, e. g. ATMega 1284: 0x200 (512 pages * 256 Bytes --> 128 KByte)
- Byte 9, 10: EEProm size, e. g. ATMega 1284: 0x1000 (4 KByte)
- Byte 11: Low Fuses
- Byte 12: Extended Fuses
- Byte 13: High Fuses
- Byte 14: Lock Bits
- Byte 15: reserved, always 0
Report 1 write:
- Byte 0: Bit1 set: Bootloader, Bit 1 not set: jump to application
- Byte 1: Interface Version, currently 1
- Byte 2: Address type for next Report 2 read / write operation, E: EEProm, F: Flash
- Byte 3 - 6: Address (in Bytes) for next read/write Report 2 operation
- Byte 7 - 15: reserved, should be 0
Report 2 read:
- Byte 0: length of data, typically 32
- Byte 1: crc over the data block
- Byte 2 - 33: data as specified in the last Report 1 write, the address
is incremented automatically, the host must submit a Report 1 write if the
memory crosses a 64KByte border.
Report 2 write:
- Byte 0: length of data, typically 32
- Byte 1: crc over the data block
- Byte 2 - 33: data as specified in the last Report 1 write, the address
is incremented automatically, the host must submit a Report 1 write if the
memory crosses a 64KByte border.
Installation
Download UsbBootLoader.zip and
unpck the contents to your BASE_FOLDER as described above.
Known issues
It may happen very rare that the software USB disconnects while flashing
the application on ATMega 1284p devices (never saw it with ATMega 328p). I guess that this is a
timing issue when disabling interrupts to write the device, but I could not yet fix it,
all interrupts are re-enabled as fast as possible...
I therefor recommend to burn the BOOTRST fuse (please also set the parameter BUILD_OPTIONS="-DBOOTRST=1")
to start the µController in the bootsection.
Reset the µController if this happens, the USB should reconnect, and you may flash
the application again.
Version Info
- V 1.0.0, 1 Aug 16: First published
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