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HUAWEI ME909u-521 LTE LGA Module
Application Guide
Sleeping and Waking Up Application Scenarios
Issue 01 (2013-07-05)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
56
Figure 8-6 Sleep procedure
8.3.2 USB and Sleep
USB is an important communication channel between the module and the host.
According to the USB protocol, normally a hub or a root hub periodically sends Start
of Frame (SOF) data packages (one data package per ms using full-speed USB and
one package per 125 µs using high-speed USB). Through this mechanism, USB
always votes to stop the module from entering sleep mode.
When the USB driver provided by Huawei detects that the module and the host have
not exchanged data in 5 seconds, the USB driver will enable the port's suspend
feature, stopping SOF data packages being sent and suspending the USB controller.
This enables the USB to vote to agree the module's sleep.