Difference between revisions of "Rpi Low-level peripherals"

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[[Category: RaspberryPi]]
#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] ]]
The Rpi allows peripherals and expansion boards (such as the upcoming [[Rpi Gertboard]]) to access the CPU by exposing the in and outputs. The production board has a 26-pin 2.54mm (100mil)<ref>http://www.raspberrypi.org/forum/features-and-requests/easy-gpio-hardware-software/page-3/#p31907</ref> 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>
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.
It is also possible to reconfigure some of the pins to provide a second I2C interface. [no-ref]
Kernel boot messages go to the UART at 115200bps.
'''Header Pinout:'''
{| border="1" style="text-align:center;"
| '''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>
| '''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
{| border="1"
! Colour legend
| bgcolor="red" | <span style="color:white">+5V</span>
| bgcolor="orange" | +3.3V
| Do not connect
| bgcolor="yellow" | UART
| bgcolor="lime" | GPIO
| bgcolor="purple" | <span style="color:white">SPI</span>
| bgcolor="cyan" | I2C
==Power pins==
Maximum permitted current draw from the 3v3 pin is 50mA.
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>
*Model A: 1000mA - 500mA -> max power draw: 500mA
*Model B: 1000mA - 700mA -> max power draw: 300mA
==General Purpose Input/Output (GPIO)==
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].
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>
At least some of the GPIO pins support PWM.<ref>http://twitter.com/#!/Raspberry_Pi/status/140548306886602752</ref>
Each GPIO can interrupt, high/low/rise/fall/change.<ref>http://www.raspberrypi.org/archives/384#comment-5217</ref>
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>
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>
===Driver support===
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>
The Foundation will not include an 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>
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>
===Code examples===
[http://www.raspberrypi.org/forum/educational-applications/gertboard/page-4/#p31555 Gert van Loo & Dom, has provided] some tested code which accesses the GPIO pins through direct GPIO register manipulation in C-code.
(Thanks to Dom for doing the difficult work of finding and testing the mapping.)
Example GPIO code:
//  How to access GPIO registers from C-code on the Raspberry-Pi
//  Example program
//  15-January-2012
//  Dom and Gert
// Access from ARM Running Linux
#define BCM2708_PERI_BASE        0x20000000
#define GPIO_BASE                (BCM2708_PERI_BASE + 0x200000) /* GPIO controller */
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <dirent.h>
#include <fcntl.h>
#include <assert.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#define PAGE_SIZE (4*1024)
#define BLOCK_SIZE (4*1024)
int  mem_fd;
char *gpio_mem, *gpio_map;
char *spi0_mem, *spi0_map;
// I/O access
volatile unsigned *gpio;
// GPIO setup macros. Always use INP_GPIO(x) before using OUT_GPIO(x) or SET_GPIO_ALT(x,y)
#define INP_GPIO(g) *(gpio+((g)/10)) &= ~(7<<(((g)%10)*3))
#define OUT_GPIO(g) *(gpio+((g)/10)) |=  (1<<(((g)%10)*3))
#define SET_GPIO_ALT(g,a) *(gpio+(((g)/10))) |= (((a)<=3?(a)+4:(a)==4?3:2)<<(((g)%10)*3))
#define GPIO_SET *(gpio+7)  // sets  bits which are 1 ignores bits which are 0
#define GPIO_CLR *(gpio+10) // clears bits which are 1 ignores bits which are 0
void setup_io();
int main(int argc, char **argv)
{ int g,rep;
  // Set up gpi pointer for direct register access
  // Switch GPIO 7..11 to output mode
  * You are about to change the GPIO settings of your computer.          *
  * Mess this up and it will stop working!                              *
  * It might be a good idea to 'sync' before running this program        *
  * so at least you still have your code changes written to the SD-card! *
  // Set GPIO pins 7-11 to output
  for (g=7; g<=11; g++)
    INP_GPIO(g); // must use INP_GPIO before we can use OUT_GPIO
  for (rep=0; rep<10; rep++)
    for (g=7; g<=11; g++)
      GPIO_SET = 1<<g;
    for (g=7; g<=11; g++)
      GPIO_CLR = 1<<g;
  return 0;
} // main
// Set up a memory regions to access GPIO
void setup_io()
  /* open /dev/mem */
  if ((mem_fd = open("/dev/mem", O_RDWR|O_SYNC) ) < 0) {
      printf("can't open /dev/mem \n");
      exit (-1);
  /* mmap GPIO */
  // Allocate MAP block
  if ((gpio_mem = malloc(BLOCK_SIZE + (PAGE_SIZE-1))) == NULL) {
      printf("allocation error \n");
      exit (-1);
  // Make sure pointer is on 4K boundary
  if ((unsigned long)gpio_mem % PAGE_SIZE)
    gpio_mem += PAGE_SIZE - ((unsigned long)gpio_mem % PAGE_SIZE);
  // Now map it
  gpio_map = (unsigned char *)mmap(
  if ((long)gpio_map < 0) {
      printf("mmap error %d\n", (int)gpio_map);
      exit (-1);
  // Always use volatile pointer!
  gpio = (volatile unsigned *)gpio_map;
} // setup_io
==MIPI CSI-2==
On the production board, we bring out the MIPI CSI-2 interface to pads for an unpopulated 15-way flat flex connector
is Sony sub-LVDS same as MIPI CSI-2? Sony IMX020 5Mbip module is available for $5-7 (SE K850i replacement camera).
Looks like Nokia N95 uses CSI-2 5Mpix camera module with autofocus. ~$15 replacement part.
On the production board, we bring out the DSI interface to pads for an unpopulated 15-way flat flex connector
[[CEC (Consumer Electronics Control) over HDMI|HDMI-CEC (Consumer Electronics Control for HDMI)]] is supported by hardware but some driver work will be needed and currently isn't exposed into Linux userland.
Eben notes that he has seen CEC demos on the Broadcom SoC they are using.
For more information about HDMI-CEC and what you could do with it on the Raspberry Pi please see the [[CEC (Consumer Electronics Control) over HDMI]] article.
== References ==
{{Template:Raspberry Pi}}

Latest revision as of 13:17, 28 January 2012