SAM4L Datasheet, PDF (343/1185 Pages) ATMEL Corporation – ATSAM ARM-based Flash MCU

ATSAM4L4/L2
17.6.2.10
Remote wakeup
The remote wakeup request (also known as upstream resume) is the only request the device
may send on its own initiative. This should be preceded by a DEVICE_REMOTE_WAKEUP
request from the host.
• First, the USBC must have detected a “Suspend” state on the bus, i.e. the remote wakeup
request can only be sent after a SUSP interrupt has been set.
• The user may then write a one to the remote wakeup (RMWKUP) bit in UDCON to send an
Upstream Resume to the host initiating the wakeup. This will automatically be done by the
controller after 5ms of inactivity on the USB bus.
• When the controller sends the Upstream Resume, the Upstream Resume (UPRSM) interrupt
is set and SUSP is cleared.
• RMWKUP is cleared at the end of the transmitting Upstream Resume.
• In case of a rebroadcast resume initiated by the host, the End of Resume (EORSM) interrupt
is set when the rebroadcast resume is completed.
17.6.2.11
RAM management
Endpoint data can be physically allocated anywhere in the embedded RAM. The USBC control-
ler accesses these endpoints directly through the HSB master (built-in DMA).
The USBC controller reads the USBC descriptors to know where each endpoint is located. The
base address of the USBC descriptor (UDESC.UDESCA) needs to be written by the user. The
descriptors can also be allocated anywhere in the embedded RAM.
Before using an endpoint, the user should setup the endpoint address for each bank. Depending
on the direction, the type, and the packet-mode (single or multi-packet), the user should also ini-
tialize the endpoint packet size, and the endpoint control and status fields, so that the USBC
controller does not compute random values from the RAM.
When using an endpoint the user should read the UESTAX.CURRBK field to know which bank
is currently being processed.
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