beagleboard url

Basic I/O with the TinCanTools Beacon Board

Jason Kridner, [email protected]
Wednesday, September 28, 2011, 9:15AM
Embedded Systems Conference Boston
Room 210

Some improvements courtesy of:
Marco Casaroli, [email protected]
Nuncio Perrella, [email protected]

Slides available at
http://beagleboard.org/esc/boston2011/beaconbasicio

Abstract

 

Learn about the basics of utilizing drivers in Linux to perform simple I/O tasks including GPIO communications. The TinCanTools Beacon Board will be used as an example to let you test your ability to control and time signals on your BeagleBoard-xM's expansion port.

Getting Started

 

What is the baseline?

http://refspecs.linuxfoundation.org/lsb.shtml

lsb_release

 

root@beagleboard:~# lsb_release -a
Distributor ID: Angstrom
Description:    Angstrom GNU/Linux 2011.03 (Dureza)
Release:        2011.03
Codename:       Dureza

Filesystem Hierarchy Standard

http://www.pathname.com/fhs/

Filesystem Hierarchy Standard

http://www.pathname.com/fhs/

/proc

 

root@beagleboard:~# ls /proc
1     1151  1214  183  44   87         consoles     kpageflags    sys
10    1160  1215  184  47   9          cpu          loadavg       sysrq-trigger
1021  1171  1218  19   48   901        cpuinfo      locks         sysvipc
1026  1172  1242  2    49   946        crypto       meminfo       timer_list
1029  1177  1251  20   5    950        devices      misc          timer_stats
1031  1182  1254  21   50   953        diskstats    modules       tty
1034  1183  1256  22   51   956        driver       mounts        uptime
1039  1187  1259  23   52   965        execdomains  mtd           version
1048  1190  1262  24   53   966        fb           net           vmallocinfo
1049  1192  1282  25   57   967        filesystems  pagetypeinfo  vmstat
1061  1193  1295  26   58   993        fs           partitions    zoneinfo
1074  12    1296  27   59   996        interrupts   sched_debug
1076  1203  13    28   6    asound     iomem        schedstat
1077  1205  1301  29   61   atags      ioports      scsi
1081  1207  14    3    62   buddyinfo  irq          self
1083  1209  15    30   644  bus        kallsyms     slabinfo
11    1211  16    31   7    cgroups    key-users    softirqs
1102  1212  17    32   8    cmdline    kmsg         stat
1121  1213  18    43   857  config.gz  kpagecount   swaps

/proc

 

root@beagleboard:~# cat /proc/cpuinfo 
Processor       : ARMv7 Processor rev 2 (v7l)
BogoMIPS        : 996.74
Features        : swp half thumb fastmult vfp edsp thumbee neon vfpv3 
CPU implementer : 0x41
CPU architecture: 7
CPU variant     : 0x3
CPU part        : 0xc08
CPU revision    : 2

Hardware        : OMAP3 Beagle Board
Revision        : 0020
Serial          : 0000000000000000

The file interface abstraction

 

Busybox

The Swiss Army Knife of Embedded Linux

http://www.busybox.net

Kernel.org documentation

http://www.kernel.org/doc/

Kernel Application Binary Interface

http://www.kernel.org/doc/Documentation/ABI/

Kernel Application Binary Interface

http://www.kernel.org/doc/Documentation/ABI/

Syscalls

http://www.kernel.org/doc/man-pages/online/pages/man2/syscalls.2.html

What is SYSFS?

 

/sys/module

http://www.kernel.org/doc/Documentation/ABI/stable/sysfs-module

/sys/class/leds

http://www.kernel.org/doc/Documentation/ABI/testing/sysfs-class-led

/sys/class/gpio

http://www.kernel.org/doc/Documentation/ABI/testing/sysfs-gpio

GPIOs

readgpio

# cd /sys/class/gpio
# ls
# echo "174" > export
# ls
# echo "in" > gpio174/direction
# cat gpio174/value
# echo "40" > export
# ls
# echo "out" > gpio40/direction
# cat gpio40/value
# echo "1" > gpio40/value
# cat gpio40/value

Reading events

 

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char** argv)
{
    int fd, ret, data[64];
    fd = ret = open(argv[argc - 1], O_RDONLY);
    printf("open returned %d\n", ret);
    while (1) {
        ret = read(fd, &data, sizeof(data));
        printf("read returned %d bytes\n", ret);
        sleep(1);
    }
    exit(0);
}

Reading events

 

root@beagleboard:~# cd ~/labs/event
root@beagleboard:~/labs/event# gcc -o myread myread.c
root@beagleboard:~/labs/event# ./myread /dev/input/touchscreen0
open returned 3
read returned 80 bytes
read returned 240 bytes
read returned 256 bytes
read returned 256 bytes
read returned 256 bytes
read returned 144 bytes
^C

Reading events

testuserbtn

Reading events

 

root@beagleboard:~/labs# evtest /dev/input/event0
Input driver version is 1.0.1
Input device ID: bus 0x19 vendor 0x1 product 0x1 version 0x100
Input device name: "gpio-keys"
Supported events:
  Event type 0 (Sync)
  Event type 1 (Key)
    Event code 276 (ExtraBtn)
Testing ... (interrupt to exit)
Event: time 1307366684.251618, type 1 (Key), code 276 (ExtraBtn), value 1
Event: time 1307366684.251649, -------------- Report Sync ------------
Event: time 1307366684.348203, type 1 (Key), code 276 (ExtraBtn), value 0
Event: time 1307366684.348234, -------------- Report Sync ------------

Access monitor EDID EEPROM

testedid

# opkg install i2c-tools
# i2cdump -y 0x3 0x50 b

Access monitor EDID EEPROM

i2c.c

#include ...
#define DATA_LEN 256

int main()
{
        int file;
        unsigned int i;
        char buf[DATA_LEN];

        file = open("/dev/i2c-3", O_RDWR);
        if (file < 0)                          exit(1);
        if (ioctl(file, I2C_SLAVE, 0x50) < 0)  exit(1);
        if (read(file, buf, DATA_LEN-1) < 1)   exit(1);
        else
                for (i=0;i<DATA_LEN-1;i++)
                        printf("%c", buf[i]);
        return 0;
}

USB OTG and EHCI

 

# cd /sys/bus/usb/devices
# ls
# cat usb1/speed
# cat usb?/manufacturer
# lsusb

Discovering USBFS

 

root@beagleboard:~# cat /sys/module/usbcore/parameters/usbfs_snoop
N
root@beagleboard:~# echo Y > /sys/module/usbcore/parameters/usbfs_snoop
root@beagleboard:~# mount -t usbfs none /mnt
root@beagleboard:~# ls /mnt
001  Devices
root@beagleboard:~/labs# cat /mnt/devices
T:  Bus=01 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=  1 Spd=480  MxCh= 3
B:  Alloc=  0/800 us ( 0%), #Int=  3, #Iso=  0
D:  Ver= 2.00 Cls=09(hub  ) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
P:  Vendor=1d6b ProdID=0002 Rev= 2.06
S:  Manufacturer=Linux 2.6.39 ehci_hcd
S:  Product=OMAP-EHCI Host Controller
S:  SerialNumber=ehci-omap.0
C:* #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=  0mA
I:* If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub
E:  Ad=81(I) Atr=03(Int.) MxPS=   4 Ivl=256ms
T:  Bus=01 Lev=02 Prnt=02 Port=03 Cnt=03 Dev#=  5 Spd=1.5  MxCh= 0
D:  Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
P:  Vendor=093a ProdID=2510 Rev= 1.00
S:  Manufacturer=PixArt
S:  Product=USB Optical Mouse
C:* #Ifs= 1 Cfg#= 1 Atr=a0 MxPwr=100mA
I:* If#= 0 Alt= 0 #EPs= 1 Cls=03(HID  ) Sub=01 Prot=02 Driver=usbhid
E:  Ad=81(I) Atr=03(Int.) MxPS=   4 Ivl=10ms

Device nodes

 

Is everything really just a file?

 

Toggle an LED with SYSFS

 

# cd /sys/class/leds/
# ls
beagleboard::pmu_stat  beagleboard::usr0  beagleboard::usr1
# cd beagleboard\:\:usr0
# ls
brightness  device  max_brightness  power  subsystem  trigger  uevent
# cat trigger
none nand-disk mmc0 [heartbeat]
echo "none" > trigger
# echo "1" > brightness
# echo "0" > brightness
# echo "heartbeat" > trigger

What is a Beacon Board?

eLinux.org/BeaconBoard

Beacon Board

How is it wired?

 

7 Segment Display

Pin Function Beagle
14 CLOCK GPIO161
16 LATCH GPIO162
10 DATA GPIO145


RGB LED

Pin Function Beagle
12 DATA GPIO158
18 CLOCK GPIO159

Read BeaconBoard I2C EEPROM

 

root@beagleboard:~# cd ~/labs/i2c
root@beagleboard:~/labs/i2c# ls
root@beagleboard:~/labs/i2c# rm i2c
root@beagleboard:~/labs/i2c# cat i2c.c
root@beagleboard:~/labs/i2c# gcc -o i2c i2c.c
root@beagleboard:~/labs/i2c# ./i2c
  

Note: By the BeagleBoard expansion board registry, these boards are meant to have a Vendor ID of 1 and a Device ID of 5, but the EEPROMs don't appear to have been programmed. You will notice, however, that you won't read any values if the board is not plugged in.

Verifying the pin mux

DM3730 TRM

root@beagleboard:~/labs/i2c# cd
root@beagleboard:~# mount -t debugfs none /sys/kernel/debug/
root@beagleboard:~# ls /sys/kernel/debug/ -w 40
asoc	   memblock   sched_features
bdi	   mmc0       smartreflex
bluetooth  musb       usb
clock	   omap_mux   vram
extfrag    omapdss    wakeup_sources
gpio	   pm_debug
hid	   regulator
root@beagleboard:~# less /sys/kernel/debug/omap_mux/board/core 
root@beagleboard:~# devmem2 0x48002174 w 0x00040118
root@beagleboard:~# less /sys/kernel/debug/omap_mux/board/core 
  

Let's see some lights!

 

root@beagleboard:~# cd ~/labs/beacon
root@beagleboard:~/labs/beacon# ls
root@beagleboard:~/labs/beacon# nano beacon_demo.js
root@beagleboard:~/labs/beacon# ./beacon_demo.js
  

Summary