Difference between revisions of "Rpi Low-level peripherals"

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[[Category: RaspberryPi]]
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#REDIRECT [[RPi Low-level peripherals]]
[[File:GPIOs.gif|thumb|254px|right|the layout of the Rpi GPIO's, not colour coded to the table. [https://sites.google.com/site/burngatehouse/home/drawings/GPIOs.gif Source] ]]
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The Rpi allows peripherals and expansion boards to access the CPU by exposing the in and outputs. The production board has a 26-pin 1.27mm (50mil) expansion header, arranged in a 2x13 strip. They provide 8 GPIO pins plus access to I2C, SPI, UART), as well as +3V3, +5V and GND supply lines.  Pin one is column 0 on the bottom row. <ref>http://www.raspberrypi.org/archives/384</ref>
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Voltage levels are 3v3.  There is no over-voltage protection on the board - the intention is that people interested in serious interfacing will use an external board with buffers, level conversion and analog I/O rather than soldering directly onto the main board.
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It is also possible to reconfigure some of the pins to provide a second I2C interface. [no-ref]
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Kernel boot messages go to the UART at 115200bps.
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'''Header Pinout:'''
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{| border="1" style="text-align:center;"
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| '''Top Row''' || bgcolor="red" | <span style="color:white">5V0</span> || DNC || bgcolor="black" | <span style="color:white">GND</span> || bgcolor="yellow" | TXD || bgcolor="yellow" | RXD || bgcolor="lime" | GPIO1 || DNC || bgcolor="lime" | GPIO4 || bgcolor="lime" | GPIO5 || DNC || bgcolor="lime" | GPIO6 || bgcolor="purple" | <span style="color:white">SPI_CE0_N</span> || bgcolor="purple" | <span style="color:white">SPI_CE1_N</span>
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|-
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| '''Bottom Row''' || bgcolor="orange" | 3V3 || bgcolor="cyan" | SDA0 || bgcolor="cyan" | SCL0 || bgcolor="lime" | GPIO7 || DNC || bgcolor="lime" | GPIO0 || bgcolor="lime" | GPIO2 || bgcolor="lime" | GPIO3 || DNC || bgcolor="purple" | <span style="color:white">SPI_MOSI</span> || bgcolor="purple" | <span style="color:white">SPI_MISO</span> || bgcolor="purple" | <span style="color:white">SPI_SCLK</span> || DNC
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|}
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{| border="1"
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! Colour legend
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|-
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| bgcolor="red" | <span style="color:white">+5V</span>
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|-
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| bgcolor="orange" | +3.3V
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|-
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| Do not connect
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|-
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| bgcolor="yellow" | UART
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|-
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| bgcolor="lime" | GPIO
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|-
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| bgcolor="purple" | <span style="color:white">SPI</span>
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|-
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| bgcolor="cyan" | I2C
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|}
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==Power pins==
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Maximum permitted current draw from the 3v3 pin is 50mA.
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Maximum permitted current draw from the 5v pin is the USB input current (usually 1A) minus any current draw from the rest of the board.<ref>http://www.raspberrypi.org/forum?mingleforumaction=viewtopic&t=1536#postid-21841</ref>
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*Model A: 1000mA - 500mA = 500mA
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*Model B: 1000mA - 700mA = 300mA
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==General Purpose Input/Output (GPIO)==
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General Purpose Input/Output (a.k.a. GPIO) is a generic pin on a chip whose behavior (including whether it is an input or output pin) can be controlled (programmed) through software. For more information see:[http://en.wikipedia.org/wiki/GPIO the wikipedia article].
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On the production board, all the UART, SPI and I2C pins can be reconfigured as GPIO pins, to provide a total of 17 GPIO pins.<ref>http://www.raspberrypi.org/archives/384</ref>
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At least some of the GPIO pins support PWM.<ref>http://twitter.com/#!/Raspberry_Pi/status/140548306886602752</ref>
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Each GPIO can interrupt, high/low/rise/fall/change.<ref>http://www.raspberrypi.org/archives/384#comment-5217</ref>
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It is also possible to reconfigure some of the pins to provide an ARM JTAG interface.<ref>http://www.raspberrypi.org/forum?mingleforumaction=viewtopic&t=1288.1</ref>
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It is also possible to reconfigure some of the pins to provide an I2S or PCM interface.<ref>http://www.raspberrypi.org/forum?mingleforumaction=viewtopic&t=1288.2</ref>
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===Driver support===
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The Foundation will not include a GPIO driver in the initial release, standard linux GPIO drivers should work with minimal modification.<ref>http://www.raspberrypi.org/forum?mingleforumaction=viewtopic&t=1278.0</ref>
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The Foundation will not include a SPI driver in the initial release, we hope the community might write one.<ref>http://www.raspberrypi.org/forum?mingleforumaction=viewtopic&t=1278.0</ref>
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The Foundation will not include an I2C driver in the initial release, we hope the community might provide one, standard linux I2C drivers should work with minimal modification.<ref>http://www.raspberrypi.org/forum?mingleforumaction=viewtopic&t=1202</ref>
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===Code examples===
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Example GPIO code:
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<pre>
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//
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//  How to access GPIO registers from C-code on the Raspberry-Pi
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//  Example program
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//  15-January-2012
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//  Dom and Gert
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//
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// Access from ARM Running Linux
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#define BCM2708_PERI_BASE        0x20000000
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#define GPIO_BASE                (BCM2708_PERI_BASE + 0x200000) /* GPIO controller */
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#include <stdio.h>
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#include <string.h>
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#include <stdlib.h>
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#include <dirent.h>
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#include <fcntl.h>
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#include <assert.h>
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#include <sys/mman.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <unistd.h>
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#define PAGE_SIZE (4*1024)
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#define BLOCK_SIZE (4*1024)
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int  mem_fd;
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char *gpio_mem, *gpio_map;
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char *spi0_mem, *spi0_map;
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// I/O access
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volatile unsigned *gpio;
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// GPIO setup macros. Always use INP_GPIO(x) before using OUT_GPIO(x) or SET_GPIO_ALT(x,y)
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#define INP_GPIO(g) *(gpio+((g)/10)) &= ~(7<<(((g)%10)*3))
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#define OUT_GPIO(g) *(gpio+((g)/10)) |=  (1<<(((g)%10)*3))
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#define SET_GPIO_ALT(g,a) *(gpio+(((g)/10))) |= (((a)<=3?(a)+4:(a)==4?3:2)<<(((g)%10)*3))
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#define GPIO_SET *(gpio+7)  // sets  bits which are 1 ignores bits which are 0
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#define GPIO_CLR *(gpio+10) // clears bits which are 1 ignores bits which are 0
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void setup_io();
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int main(int argc, char **argv)
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{ int g,rep;
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  // Set up gpi pointer for direct register access
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  setup_io();
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  // Switch GPIO 7..11 to output mode
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/************************************************************************\
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  * You are about to change the GPIO settings of your computer.          *
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  * Mess this up and it will stop working!                              *
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  * It might be a good idea to 'sync' before running this program        *
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  * so at least you still have your code changes written to the SD-card! *
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\************************************************************************/
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  // Set GPIO pins 7-11 to output
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  for (g=7; g<=11; g++)
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  {
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    INP_GPIO(g); // must use INP_GPIO before we can use OUT_GPIO
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    OUT_GPIO(g);
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  }
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  for (rep=0; rep<10; rep++)
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  {
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    for (g=7; g<=11; g++)
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    {
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      GPIO_SET = 1<<g;
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      sleep(1);
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    }
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    for (g=7; g<=11; g++)
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    {
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      GPIO_CLR = 1<<g;
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      sleep(1);
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    }
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  }
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  return 0;
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} // main
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//
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// Set up a memory regions to access GPIO
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//
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void setup_io()
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{
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  /* open /dev/mem */
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  if ((mem_fd = open("/dev/mem", O_RDWR|O_SYNC) ) < 0) {
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      printf("can't open /dev/mem \n");
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      exit (-1);
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  }
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  /* mmap GPIO */
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  // Allocate MAP block
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  if ((gpio_mem = malloc(BLOCK_SIZE + (PAGE_SIZE-1))) == NULL) {
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      printf("allocation error \n");
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      exit (-1);
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  }
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  // Make sure pointer is on 4K boundary
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  if ((unsigned long)gpio_mem % PAGE_SIZE)
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    gpio_mem += PAGE_SIZE - ((unsigned long)gpio_mem % PAGE_SIZE);
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  // Now map it
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  gpio_map = (unsigned char *)mmap(
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      (caddr_t)gpio_mem,
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      BLOCK_SIZE,
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      PROT_READ|PROT_WRITE,
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      MAP_SHARED|MAP_FIXED,
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      mem_fd,
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      GPIO_BASE
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  );
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  if ((long)gpio_map < 0) {
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      printf("mmap error %d\n", (int)gpio_map);
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      exit (-1);
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  }
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  // Always use volatile pointer!
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  gpio = (volatile unsigned *)gpio_map;
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} // setup_io
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</pre>
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==MIPI CSI-2==
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On the production board, we bring out the MIPI CSI-2 interface to pads for an unpopulated 15-way flat flex connector
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is Sony sub-LVDS same as MIPI CSI-2? Sony IMX020 5Mbip module is available for $5-7 (SE K850i replacement camera).
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Looks like Nokia N95 uses CSI-2 5Mpix camera module with autofocus. ~$15 replacement part.
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==DSI==
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On the production board, we bring out the DSI interface to pads for an unpopulated 15-way flat flex connector
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==CEC==
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HDMI-CEC is supported by hardware but some driver work will be needed and currently isn't exposed into Linux userland.
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Eben notes that he has seen CEC demos on the Broadcom SoC they are using.
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== References ==
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<references/>
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Latest revision as of 20:17, 28 January 2012