[Snappy ubuntu core ] boot was delay 1min 30s

[Pillar Zuo]

Hi,
    When I boot my snappy system every time.It need delay 1min 30s.
 [ *** ] (1 of 2) A start job is running for...0p1.device (1min 28s / 1min 30s) [ *** ] (1 of 2) A start job is running for...0p1.device (1min 29s / 1min 30s) [*** ] (1 of 2) A start job is running for...0p1.device (1min 29s / 1min 30s) [** ] (2 of 2) A start job is running for...yS0.device (1min 30s / 1min 30s) [ TIME ] Timed out waiting for device dev-ttyS0.device. 
[DEPEND] Dependency failed for Serial Getty on ttyS0. 
[ TIME ] Timed out waiting for device dev-mmcblk0p1.device. 
[DEPEND] Dependency failed for /boot/uboot. 
[DEPEND] Dependency failed for Local File Systems.

I have check /dev/ttyS0, and /dev/mmcblk0p1 devices. which is OK.
root at localhost:~# ls /dev/ttyS0 
/dev/ttyS0 
root at localhost:~# 
root at localhost:~# ls /dev/mmcblk0p 
mmcblk0p1 mmcblk0p2 mmcblk0p3 mmcblk0p4 
root at localhost:~# ls /dev/mmcblk0p1

How can I cancel the delay time?
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