sleep to avoid udev race condition #185

sleep 100 ms after export to avoid race condition as udev
needs the opportunity to set group ownership and permission

Test instructions:
==================
reboot, log back in, wait for udev to set group ownership and permission:

$ ls -la /sys/devices/platform/ocp/48304000.epwmss/48304200.pwm/pwm/pwmchip6/export
-rw-rw---- 1 root pwm 4096 Nov  2 04:02 /sys/devices/platform/ocp/48304000.epwmss/48304200.pwm/pwm/pwmchip6/export

run test program:

python ~/issue185.py

contents of test program:

import Adafruit_BBIO.PWM as PWM
PWM.start("P8_13", 50, 1000, 0)
PWM.stop("P8_13")
PWM.cleanup()

source/c_pwm.c

@@ -412,6 +412,10 @@ BBIO_err pwm_setup(const char *key, __attribute__ ((unused)) float duty, __attri
             }
             fprintf(f, "%d", p->index);
             fclose(f);
+            /* sleep to avoid race condition as udev needs the
+               opportunity to set group ownership and permission */
+            syslog(LOG_DEBUG, "Adafruit_BBIO: pwm_start: sleep 100 ms after export to avoid udev race condition");
+            usleep(100 * 1000); /* 100 ms */
         } else {
             syslog(LOG_ERR, "Adafruit_BBIO: pwm_setup: %s couldn't stat %s: %i-%s",
                    key, pwm_path, errno, strerror(errno));