AT8xC51SND2C
Upstream Resume
A USB device can be allowed by the Host to send an upstream resume for Remote
Wake-up purpose.
When the USB controller receives the SET_FEATURE request:
DEVICE_REMOTE_WAKEUP, the firmware should set to 1 the RMWUPE bit in the
USBCON register to enable this functionality. RMWUPE value should be 0 in the other
cases.
If the device is in SUSPEND mode, the USB controller can send an upstream resume by
clearing first the SPINT bit in the USBINT register and by setting then to 1 the SDRM-
WUP bit in the USBCON register. The USB controller sets to 1 the UPRSM bit in the
USBCON register. All clocks must be enabled first. The Remote Wake is sent only if the
USB bus was in Suspend state for at least 5ms. When the upstream resume is com-
pleted, the UPRSM bit is reset to 0 by hardware. The firmware should then clear the
SDRMWUP bit.
Figure 75. Example of REMOTE WAKEUP Management
USB Controller Init
SET_FEATURE: DEVICE_REMOTE_WAKEUP
Set RMWUPE
SPINT
Detection of a SUSPEND state
Suspend Management
need USB resume
enable clocks
Clear SPINT
Set SDMWUP
UPRSM = 1
UPRSM
upstream RESUME sent
Clear SDRMWUP
119
4341D–MP3–04/05
ATMEL [ ATMEL ]
