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avoiding usb

e14 Contributor

The usb has been measured by Dom as taking about 20% of the cpu

to service interrupts, which come at 8000 per second, even when the usb

is idle.    USB can be suspended by doing:

 

   echo 1 > /sys/devices/platform/bcm2708_usb/bussuspend

 

http://www.raspberrypi.org/phpBB3/viewtopic.php?f=28&t=7866

 

However, that prevents use of the USB keyboard.  So there is some

interest in perhaps connecting a keyboard using GPIO instead.

 

Section 2.2 of the Broadcom datasheet says:

http://www.element14.com/community/docs/DOC-43016/l/broadcom-datasheet-for-bcm2835-soc-used-in-raspberry-pi

 

"The mini UART is a secondary low throughput UART intended to be used as a console."

Anyone know how difficult it would be to rig this up?

Parents

  • There are several ways to approach this, it May be possible to get a PS2 keyboard to work using this UART, but you could also Make a serial keyboard too, in fact the Arduino is perfectly able to do this, an 8x8 matrix array using the keypad library and then output this as serial data directly to the UART would give you 64 keys.

    or you you could use a PC and a terminal emulator, or even buy an old dedicated terminal, some are even handheld with an LCD screen for local echo.

     

    I don`t really know much about the Pi, but i`m wondering if you Did need to use USB, if one of these 4 way HUB/Splitters would work on it?

Reply

  • There are several ways to approach this, it May be possible to get a PS2 keyboard to work using this UART, but you could also Make a serial keyboard too, in fact the Arduino is perfectly able to do this, an 8x8 matrix array using the keypad library and then output this as serial data directly to the UART would give you 64 keys.

    or you you could use a PC and a terminal emulator, or even buy an old dedicated terminal, some are even handheld with an LCD screen for local echo.

     

    I don`t really know much about the Pi, but i`m wondering if you Did need to use USB, if one of these 4 way HUB/Splitters would work on it?

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