USBaspLoader-tiny85 is a modification to the USBaspLoader project giving support for the ATtiny85 microcontroller. This is a signification modification as the tiny85 has very limited boot loader support in the hardware. The boot loader becomes a part of the application it has loaded by taking over the application's reset and USB-related interrupt vectors, yet the application does not need to be modified to support the boot loader. The boot loader does take up more flash (about 2.8k) than the standard USBaspLoader (about 2k), so the space available for the application is smaller.
Because of the limited pin count on the tiny85, the boot loader doesn't look for an external condition to enter boot loader mode, it does it automatically before starting the application. On reset the boot loader enumerates with the PC as a USBasp programmer, and jumps to the application after 5 seconds if there are no USBasp commands sent by the PC. You can flash the device with AVRDUDE through a "virtual" USBasp programmer. If there is no valid application loaded (determined by verifying a checksum calculation across application program space) the boot loader will stay connected as a USBasp programmer until the flash is written.
Even through the ATtiny85 only has 6 IO pins, there are a couple ways designers have connected the USB signals to the tiny85.
Configuration 1 The first configuration this bootloader supported was the configuration used by the V-USB example "EasyLogger", and by Sparkfun in their AVR Stick: D- is connected to PB0 and D+ is connected to PB2 (INT0). This is convenient as INT0 can be used for USB, and the Pin Change interrupts can be left free for the application to use, but inconvienient as INT0 shares the same pin as USCK/SCL preventing use of the USI peripheral in SPI or I2C mode. Also, PB0 is used for MOSI/DI/SDA, preventing use of the USI peripheral in UART mode as well as SPI and I2C.
Configuration 2 An alternate configuration, used by Little Wire, puts the D+ pin on PB4 and D- on PB3, and uses Pin Change interrupts instead of INT0 for USB. This allows the USI peripheral to be used by the application, but prevents using external interrupts: Pin Change interrupts are used by USB, and INT0 shouldn't be used as it's a higher priority interrupt than Pin Change, and will interfere with USB communication.
(There's a third configuration used by vusbtiny: similar to configuration 2 but with the D- and D+ pins swapped. I don't plan to support that configuration in the precompiled binaries, though it can be generated easily by changing bootloaderconfig.h and recompiling.)
For more information on the USBaspLoader-tiny85, please visit the following URL:
http://www.embeddded-creations.com
(c) 2012 Louis Beaudoin
Below is the unmodified README file for USBaspLoader:
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This is the README file for USBaspLoader.
USBaspLoader is a USB boot loader for AVR microcontrollers. It can be used on all AVRs with at least 2 kB of boot loader section, e.g. the popular ATMega8. The firmware is flashed into the upper 2 kB of the flash memory and takes control immediately after reset. If a certain hardware condition is met (this condition can be configured, e.g. a jumper), the boot loader waits for data on the USB interface and loads it into the remaining part of the flash memory. If the condition is not met, control is passed to the loaded firmware.
This boot loader is similar to Thomas Fischl's avrusbboot and our own bootloadHID, but it requires no separate command line tool to upload the data. USBaspLoader emulates Thomas Fischl's USBasp programmer instead. You can thus use AVRDUDE to upload flash memory data (and if the option is enabled) EEPROM data.
Since USBaspLoader cooperates with AVRDUDE, it can be used in conjunction with the Arduino software to upload flash memory data.
Readme.txt ........ The file you are currently reading. firmware .......... Source code of the controller firmware. firmware/usbdrv ... USB driver -- See Readme.txt in that directory for info License.txt ....... Public license (GPL2) for all contents of this project. Changelog.txt ..... Logfile documenting changes in soft-, firm- and hardware.
This project can be built on Unix (Linux, FreeBSD or Mac OS X) or Windows.
For all platforms, you must first describe your hardware in the file "firmware/bootloaderconfig.h". See the documentation in the example provided with this distribution for details. Then edit "firmware/Makefile" to reflect the target device, the device's boot loader address and fuse bit values.
Building on Windows: You need WinAVR for the firmware, see http://winavr.sourceforge.net/. To build the firmware with WinAVR, change into the "firmware" directory, check whether you need to edit the "Makefile" (e.g. change device settings, programmer hardware, clock rate etc.) or bootloaderconfig.h and type "make" to compile the source code. Before you upload the code to the device with "make flash", you should set the fuses with "make fuse". To protect the boot loader from overwriting itself, set the lock bits with "make lock" after uploading the firmware.
Building on Unix (Linux, FreeBSD and Mac): You need the GNU toolchain and avr-libc for the firmware. See http://www.nongnu.org/avr-libc/user-manual/install_tools.html for a good description on how to install the GNU compiler toolchain and avr-libc on Unix. For Mac OS X, we provide a read-made package, see http://www.obdev.at/avrmacpack/
To build the firmware, change to the "firmware" directory, edit "Makefile" and bootloaderconfig.h as described in the Windows paragraph above and type "make" to compile the source code. Before you upload the code to the device with "make flash", you should set the fuses with "make fuse". Then protect the boot loader firmware with "make lock".
The boot loader is quite easy to use. Set the jumper (or whatever condition you have configured) for boot loading on the target hardware, connect it to the host computer and (if not bus powered) issue a Reset on the AVR.
You can now flash the device with AVRDUDE through a "virtual" USBasp programmer.
This project is not intended as a reference implementation. If you want to use AVR-USB in your own projects, please see
It is our intention to make our USB driver and this demo application available to everyone. Moreover, we want to make a broad range of USB projects and ideas for USB devices available to the general public. We therefore want that all projects built with our USB driver are published under an Open Source license. Our license for the USB driver and demo code is the GNU General Public License Version 2 (GPL2). See the file "License.txt" for details.
If you don't want to publish your source code under the GPL2, you can simply pay money for AVR-USB. As an additional benefit you get USB PIDs for free, licensed exclusively to you. See the file "CommercialLicense.txt" in the usbdrv directory for details.
For more information about Objective Development's firmware-only USB driver for Atmel's AVR microcontrollers please visit the URL
http://www.obdev.at/products/avrusb/A technical documentation of the driver's interface can be found in the file "firmware/usbdrv/usbdrv.h".
-- (c) 2008 by OBJECTIVE DEVELOPMENT Software GmbH. http://www.obdev.at/