Marco Casaroli, marco@intelliges.com.br
Nuncio Perrella, n-perrella@ti.com
August 31, 2011, 14:30
TI Tech Day São Paulo - Moema Room
Based on original work by Jason Kridner, jdk@ti.com
Typical introductions to embedded Linux focus on complex tasks like building device drivers that are highly desired by at least some people working on your Linux product team. What about the rest of us that simply want to build a quick understanding of how to do some of the simple tasks that are trivial in microcontrollers without using operating systems, like accessing GPIO pins and performing I2C or SPI serial communications? This class takes a quick top-down overview from the perspective of an electrical engineer looking to take advantage of the latest in GUI building technologies, like Android, Qt, and HTML5, without completely losing access to the underlying hardware for simple system integration tasks.
root@beagleboard:~# lsb_release -a Distributor ID: Angstrom Description: Angstrom GNU/Linux 2011.03 (Dureza) Release: 2011.03 Codename: Dureza
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
root@beagleboard:~# cat /proc/cpuinfo Processor : ARMv7 Processor rev 2 (v7l) BogoMIPS : 246.33 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
8250 input_polldev omapdss snd ubi auth_rpcgss ipv6 omapfb snd_pcm ubifs block kernel oprofile snd_pcm_oss uinput bluetooth keyboard printk snd_rawmidi usb_storage btusb lockd psmouse snd_timer usbcore dns_resolver mmc_core rfcomm snd_usb_audio usbhid eeprom_93cx6 mmcblk rfkill soundcore videobuf_core ehci_hcd mousedev scsi_mod spidev vpfe_capture hci_uart musb_hdrc sg spurious vt hid netpoll smc911x sr_mod xz_dec hid_apple nfs smc91x sunrpc hid_ntrig omap3_isp smsc911x tcp_cubic hidp omap_vout smsc95xx uas
# 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
#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);
}
root@beagleboard:~/labs# gcc -o myread myread.c root@beagleboard:~/labs# ./myread /dev/input/event0 open returned 3 read returned 32 read returned 32 read returned 32
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 ------------
# opkg install i2c-tools # i2cdump -y 0x3 0x50 b
#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;
}
# cd /sys/bus/usb/devices # ls # cat usb1/speed # cat usb?/manufacturer # lsusb
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
#include <QtGui>
int main( int argc, char *argv[] )
{
QApplication myapp( argc, argv );
QLabel *mylabel = new
QLabel("Helloworld");
mylabel->show();
return myapp.exec();
}
# 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
root@beagleboard:~/lab# cd /home/root/lab root@beagleboard:~/lab# ls root@beagleboard:~/lab# rm i2c root@beagleboard:~/lab# cat i2c.c root@beagleboard:~/lab# make i2c root@beagleboard:~/lab# ./i2c
root@beagleboard:~/lab# cd qt root@beagleboard:~/lab/qt# ls root@beagleboard:~/lab/qt# make distclean ... root@beagleboard:~/lab/qt# ls (inspect the files...) root@beagleboard:~/lab/qt# designer led.ui root@beagleboard:~/lab/qt# cat main.cpp root@beagleboard:~/lab/qt# gedit led.cpp root@beagleboard:~/lab/qt# . /usr/share/qt4/environment-setup root@beagleboard:~/lab/qt# qmake-qt4 root@beagleboard:~/lab/qt# make root@beagleboard:~/lab/qt# ./qt