> button vup 0

ASSERTION FAILURE 'us' in usleep() at common/timer.c:163

=== PROCESS EXCEPTION: 00 ====== xPSR: 1007580f ===
r0 :000000a3 r1 :1008d580 r2 :00000001 r3 :1007e271
r4 :dead6663 r5 :000000a3 r6 :1008d580 r7 :1008b7b8
r8 :10088ec4 r9 :00000000 r10:00000000 r11:00000000
r12:00000000 sp :200c4ff8 lr :200c0a48 pc :00000000

mmfs = 0, shcsr = 70000, hfsr = 0, dfsr = 0

=========== Process Stack Contents ===========
200c5060: 00000000 00000000 00000000 00000000
200c5070: 00000000 00000000 00000000 00000000
200c5080: 00000000 10084495 deadd00d deadd00d
200c5090: deadd00d deadd00d deadd00d deadd00d

Now, you may call this user error and you would be right, but it would still be better to just print an error message there rather than taking the whole system down.