Displays and Other Outputs - BeagleBone - page 174

Discussion
The four onboard USER LEDs have a default behavior, as shown in Table 3-1 .
Table 3-1. Default LED behavior
LED Pattern
USER0 Heartbeat pattern
USER1 Flashes when the microSD is being accessed
USER2 Flashes when the CPU is busy
USER3 Flashes when the onboard flash is being accessed
When you run your code, it turns off the default action and gives you full control.