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--- hidkey_gpio [2012/11/27 02:11] – [Results] steve_m
+++ hidkey_gpio [2013/02/27 00:10] (current) – [Results] steve_m
@@ Line 1: / Line 1: @@
 ====== 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 =====
@@ Line 30: / Line 30: @@
 |Caps lock|MOSI|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.
@@ Line 36: / Line 36: @@
 ===== 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 ====
@@ Line 79: / Line 79: @@
 </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 =====
-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)!
@@ Line 145: / Line 145: @@
 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 ==