SAM4L Datasheet, PDF (342/1185 Pages) ATMEL Corporation – ATSAM ARM-based Flash MCU

ATSAM4L4/L2
17.6.2.6
17.6.2.7
17.6.2.8
17.6.2.9
Busy bank enable
In order to make an endpoint bank look busy regardless of its actual state, the user can write a
one to the Busy Bank Enable bit in the Endpoint n Control Register (UECONnSET.BUSY0/1ES).
If a BUSYnE bit is set, any transaction to this bank will be rejected with a NAK reply.
Address setup
The USB device address is set up according to the USB protocol.
• After all kinds of resets, the USB device address is 0.
• The host starts a SETUP transaction with a SET_ADDRESS(addr) request.
• The user writes this address to the USB Address field (UDCON.UADD), and writes a zero to
the Address Enable bit (UDCON.ADDEN), resulting in the address remaining zero.
• The user sends a zero-length IN packet from the control endpoint.
• The user enables the stored USB device address by writing a one to ADDEN.
Once the USB device address is configured, the controller filters the packets to only accept
those targeting the address stored in UADD.
UADD and ADDEN should not be written to simultaneously. They should be written sequentially,
UADD field first.
If UADD or ADDEN is cleared, the default device address 0 is used. UADD and ADDEN are
cleared:
• On a hardware reset.
• When the USBC is disabled (USBE written to zero).
• When a USB reset is detected.
Suspend and Wakeup
When an idle USB bus state has been detected for 3 ms, the controller sets the Suspend
(SUSP) interrupt bit in UDINT. In this case, the transceiver is suspended, reducing power
consumption.
To further reduce power consumption it is recommended to freeze the USB clock by writing a
one to the Freeze USB Clock (FRZCLK) bit in USBCON when the USB bus is in suspend mode.
The MCU can also enter the power save mode mode to further lower power consumption.
To recover from the suspend mode, the user shall wait for the Wakeup (WAKEUP) interrupt bit,
which is set when a non-idle event is detected, and then write a zero to FRZCLK.
As the WAKEUP interrupt bit in UDINT is set when a non-idle event is detected, it can occur
regardless of whether the controller is in the suspend mode or not.
Detach
The reset value of the DETACH bit located in the UDCON register, is one.
It is possible to initiate a device re-enumeration simply by writing a one and then a zero to
DETACH.
DETACH acts on the pull-up connections of the DP and DM pads. See “Device mode” for fur-
ther details.
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