hidkey_gpio
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hidkey_gpio [2012/11/27 03:11] steve_m [Results] |
hidkey_gpio [2013/02/27 01:10] steve_m [Results] |
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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. | ||
| Line 36: | Line 36: | ||
| ===== 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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| </code> | </code> | ||
| - | Well, as you can see, programming takes quite a while, mainly because of the slow input speed I mentioned before, but is very reliable. Since I assume that many people have some old USB keyboard laying around collecting dust, it still could be used as a bootstrap flasher for solving the old chicken-and-egg problem when building a faster programmer ([[http://www.fischl.de/usbasp/|USBasp]], [[http://www.ladyada.net/make/usbtinyisp/|USBtinyISP]]) or as low-speed general purpose output for other applications. For example, many outputs could be driven using a simple serial-in, parallel-out shift register. | + | Well, as you can see, programming takes quite a while, mainly because of the slow input speed I mentioned before, but is very reliable. Since I assume that many people have some old USB keyboard lying around collecting dust, it still could be used as a bootstrap flasher for solving the old chicken-and-egg problem when building a faster programmer ([[http://www.fischl.de/usbasp/|USBasp]], [[http://www.ladyada.net/make/usbtinyisp/|USBtinyISP]]) or as low-speed general purpose output for other applications. For example, many outputs could be driven using a simple serial-in, parallel-out shift register. |
| ===== 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)! | ||
| Line 145: | Line 145: | ||
| 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 == | ||
hidkey_gpio.txt · Last modified: 2013/02/27 01:10 by steve_m
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