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hidkey_gpio [2012/11/27 03:11] steve_m [Results] |
hidkey_gpio [2012/11/30 19:40] steve_m [Update #1] |
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====== AVR Programmer built from a USB Keyboard ====== | ====== AVR Programmer built from a USB Keyboard ====== | ||
- | Recently, my old keyboard became louder and louder while typing, so I decided to buy a new one. But what to do with the old one? Ever since I saw the [[http://www.pjrc.com/hub_isp/|AVR programmer that uses a USB hub]], I thought of abusing a USB keyboard for that. | + | Recently, my keyboard became louder and louder while typing, so I decided to buy a new one. But what to do with the old one? Ever since I saw the [[http://www.pjrc.com/hub_isp/|AVR programmer that uses a USB hub]], I thought of abusing a USB keyboard for that. |
===== Theory ===== | ===== Theory ===== | ||
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|Caps lock|MOSI|out| | |Caps lock|MOSI|out| | ||
|Scroll lock|Reset|out| | |Scroll lock|Reset|out| | ||
- | |row/column of right shift key|MISO|in| | + | |row/column of right shift key|MISO (through optocoupler)|in| |
For the optocoupler I added a 470Ω current limiting resistor. | For the optocoupler I added a 470Ω current limiting resistor. | ||
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===== Software ===== | ===== Software ===== | ||
- | First I wrote a small libusb-based test utility for experimenting with the keyboard. I'm directly communicating with the keyboard from userspace, unloading the kernel driver first. | + | First I wrote a [[https://github.com/steve-m/hidkey_gpio|small libusb-based test utility]] for experimenting with the keyboard. I'm directly communicating with the keyboard from userspace, unloading the kernel driver first. |
==== Speed ==== | ==== Speed ==== | ||
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===== Update #1 ===== | ===== Update #1 ===== | ||
- | Since reading the MISO input is much slower than writing the outputs, as I mentioned above, I took a closer look at the avrdude code. As it turns out, the inputs are read every time, even if the data isn't used at all (like when writing a byte). I applied a crude hack, so that MISO is only being read if the data is used afterwards. I pushed that change to a new [[https://github.com/steve-m/avrdude/tree/speedup|speedup branch]] on github. | + | Since reading the MISO input is much slower than writing the outputs, as I mentioned above, I took a closer look at the avrdude code. As it turns out, the inputs are read every time, even if the data isn't used at all afterwards (like when writing a byte). I applied a crude hack, so that MISO is only being read if the data is used afterwards. I pushed that change to a new [[https://github.com/steve-m/avrdude/tree/speedup|speedup branch]] on github. |
With those changes, flashing my 86 byte demo application is now over ten times faster (11.75s vs. 123.79s)! | With those changes, flashing my 86 byte demo application is now over ten times faster (11.75s vs. 123.79s)! | ||
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I'd say that's quite an improvement, and very well acceptable for a chicken-and-egg bootstrap flasher :-) | I'd say that's quite an improvement, and very well acceptable for a chicken-and-egg bootstrap flasher :-) | ||
+ | |||
+ | This project was featured on [[http://hackaday.com/2012/11/26/usb-keyboard-becomes-an-avr-programmer/|Hackaday]]. | ||
== Reference Literature == | == Reference Literature == |