This bootloader is based on the AVR109 application note. This programm communicates using the UART serial communication protocol, in order to execute all the data manipulation required (read, write, verify and clear operations) inside the flash and EEPROM memory of the target microcontroller.
When the microcontroller detects a flank change on the RESET pin, it will send a 3 bit string, containing the signature bytes of the device. In order to enter to the bootloader mode, an ACK (0x06) byte should be replied. If there no is valid reply within a period of 1 second (this time could be change in the source files of the bootloader configuration file 'config.h' --> 'OVRFLW'), the device will lauch the application saved on the flash address 0x0000.
Once the bootloader is actived, a limited number of commands could be send to control the behaviour of the bootloader program:
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Read Flash ('r'): This one-page-at-a-time read function, gather the data contained in one page of the device's memory. In order to perform the read action, a frame with the page address (index), and a 16 bit crc of the data is sent (3 bytes frame). The device will perform the read action and reply with a data frame of length equal to SPM_SIZE, plus 2 bytes of crc. In order to perform a full flash memory read action, this function should be perform multiple times.
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Write Flash ('w'): Is used to write data to the flash memory of the device. For this, a frame consisting of page address index, a SPM_SIZE length of data, and a 16 bit crc should be sent to the device. The writing action will be perform, and once is finished an ACK byte response should be received. To read the data written with this function on the actual session of the bootloader a 'rww enable' function has to be perform (refer to Execute flash modification). This is a 1 page-at-a-time writing function.
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Flash data verify ('v'): When a verification of the data inside the flash memory needs to be executed, this function is the one you need. A frame of 1 byte consisting of the page address index, of the next page to last byte where the data will be verified (ie. if you want to verify the data until the 0x7BFF byte -or 0x7B80 bytewise address, or 247th page in flash memory-, an address index of 248 (0x7C00 bytewise) should be sent). Followed by 2 bytes of crc. This action will perform in a complete page, so when the data in the hex file that you want to verify against the flash memory is smaller than a complete full page, the remaining bytes should be filled with 0xFF. The device will reply with a frame of 4 bytes: 2 bytes of crc, and 2 more of the complement of this crc. With this the received crc is check for data errors during transmission.
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Flash memory clear ('c'): This command will erase all the data contained in the flash memory, and will reply with and ACK byte afterwards.
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EEPROM read ('R'): Similar to Flash read, but perform on EEPROM memory.
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EEPROM write ('W'): Will update the data in the EEPROM memory (please refer to Flash write section) with the data sent. After this command a re-enable of the memory is not necessary.
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EEPROM data verify ('V'): Refer to 'Flash data verify' section.
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EEPROM clear ('C'): Will update the data on all the EEPROM memory with 0xFF bytes (erasing) the content of this memory. Will reply with and ACK, once completed.
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Execute enable of SPM pages ('X'): This will perform a RWW section enable, so the pages written to the flash memory could be read and verified before leaving the bootloader. An alternative is to perform a reset (not recommended).
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Quit bootloader ('Q'): This will simply quit the bootloader application, and jump to the application stored in the memory address 0x0000 and reply with a ACK.
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All other bytes sent to the device will result in a NACK reply. This could be used to detect that the bootloader is still active.
NOTE: Please take into consideration that the commands to read/write/verify/clear for the flash memory, are similar to the EEPROM commands, but the first are lowercase.
NOTE: When refering to the page address index, is the result of performing a division of the bytewise page address, between the SPM_SIZE.
PAGE ADDRESS / SPM_SIZE or PAGEADDRESS >> LOG2(SPM_SIZE)
The CRC calculation varies in function of the data length, using the best mask for that length and a initial value of 0xFFFF. More information avalaible on: http://users.ece.cmu.edu/~koopman/crc/
- Go to src folder
- Modify the 'Makefile' file with the data required for your device and programming tool.
- Perform a 'make' command, this will compile and link the source files.
- Run a 'make hex', this will create a hex file of the bootloader program.
- Next will be 'make install' to burn the hex file into the bootloader section of the Flash memory of the device.
- Makefile also has other commands ie. 'make clean', 'make readflash', 'make readeeprom', 'make cleanall' that could be useful in some cases.
- Is important to setup the fuses correctly on the device:
- An Boot flash section of at least 1024 words is required
- The Boot Reset Vector should be enabled
- Go to tool folder
- Run the 'avrdb.py' script (python avrdb.py or ./avrdb.py).
- A menu with the actions that could be perform are diplayed. Check if the information for your device is already in the data base, if not add it (all the information needed is in the datasheet of the device).
- Once the data is in the data base, exit the program.
- Now run
python nstbFlasher.py -h, an the help dialog will be displayed. - Next run the flasher script with all the options required for your application.
NOTE: Before any attempt of communication with the microcontroller could be established, information of signature, device name, bootloader address, SPM_SIZE, FLASHEND and EEPROM should be added to the database (avr.db), using the avrdb.py script. All this information should be checked within the datasheet of the device.
A hex file is included in the 'example' folder, this is a simple application that will toggle a led connected to the PB1 pin of the device, with a frequency of 400 ms. Please use this to test the bootloader.
Firmware Copyright (C): 2015 - Alberto Vazquez aka IcyD
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 2 of the License, or
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