1Sheeld bootloader is a small piece of firmware that come pre-installed on your 1Sheeld board and is used mainly for flashing new firmware updates to the board using the app.
1Sheelds microcontroller's (ATmega162) flash memory is divided into two sections, the boot section and the application section. Both of them contain the bootloader and the firmware respectively.
Every time the board is reset using the reset button, it will start executing the bootloader from the boot section and wait for 200ms for a request from the app to update the firmware. If the request is received, the bootloader will communicate with the app, receive the new firmware and replace the old one, it will then switch to the application section and run the new firmware. If no request is received the bootloader will exit and execute the firmware found in the application section.
The bootloader communicates with the app through serial protocol on ATmega162's UART1.
The program file is transferred in the binary format. So if the file is in Intel hex format (.hex) you have to transform it to binary (.bin) format before flashing using a tool like Hex2Bin.
The bootloader uses the standard XModem protocol with CRC16 for error checking.
Here is a breakdown of the firmware upgrading steps:
- The bootloader sends a NAK to notifies the app that it is ready for the password.
- In less than 200ms, the app sends the 8 characters password :
{0x64, 0x0E, 0x1C, 0x39, 0x14, 0x28, 0x57, 0xAA} - The bootloader sends 'C' character to notifies the app that it is using the CRC16 method.
- The app splits the binary file into 128 bytes packets and transmit them frame by frame in this format:
- an SOH byte {1 byte}
- the packet number {1 byte}
- the 1's complement of the packet number {1 byte}
- the packet {128 bytes}
- the high byte of the CRC value {1 byte}
- the low byte of the CRC value {1 byte}
- If the bootloader finds that the CRC values matches the computed ones, it flashs the packet and sends an ACK otherwise it sends a NAK.
- The app waits for an ACK to transmit the next frame or a NAK to resends the last one until the whole binary file is sent.
- After the whole binary file is sent, the app sends an EOT.
- If there are no errors, the bootloader sends an ACK.
The project is an generic C project, and can be built using any port of avr-gcc for either Microsoft Windows, Linux, or Mac OSX. Just make sure you have both GNU Make and avr-gcc tool chain installed on your platform then run make on the repo's root directory and both the debug and release versions will be built in a new subdirectory called build.
The ICSP pins are exposed with a 6-pin header on the bottom of your 1Sheeld board. You can easily connect any ATmega programmer and upload your own version of the bootloader.
If you are using any USBasp programmer and have avrdude installed, after building using make you can flash your board by running either make flashdebug or make flashrelease on the repo's root directory. Make sure you erase the chip first by running make erase.
- Low Value: 0xFD
- High Value: 0xD8
- Extended Value: 0xFB
Click here for a description of the enabled fuse bits.
Contributions are welcomed, please follow this pattern:
- Fork the repo.
- Open an issue with your proposed feature or bug fix.
- Commit and push code to a new branch in your forked repo.
- Submit a pull request to our development branch.
Don't forget to drop us an email, post on our forum, or mention us on Twitter or Facebook about what you have built using 1Sheeld, we would love to hear about it.
To see what has changed in recent versions of 1Sheeld Bootloader, see the Change Log.
1Sheeld Bootloader is based on AVR Universal Bootloader(AVRUB) by Shao Ziyang.
This code is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License version 3 only, as
published by the Free Software Foundation.
This code is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
version 3 for more details (a copy is included in the LICENSE file that
accompanied this code).
Please contact Integreight, Inc. at info@integreight.com or post on our
support forums www.1sheeld.com/forum if you need additional information
or have any questions.