Datasheet

Figure 38-3. Multi-Packet Feature - Reduction of CPU Overhead
Maximum Endpoint size
Data Payload
Without Multi-packet support
With Multi-packet support
Transfer Complete Interrupt
&
Data Processing
38.6.2.4 USB Reset
The USB bus reset is initiated by a connected host and managed by hardware.
During USB reset the following registers are cleared:
• Device Endpoint Configuration (EPCFG) register - except for Endpoint 0
• Device Frame Number (FNUM) register
• Device Address (DADD) register
• Device Endpoint Interrupt Enable Clear/Set (EPINTENCLR/SET) register
• Device Endpoint Interrupt Flag (EPINTFLAG) register
• Transmit Stall 0 bit in the Endpoint Status register (EPSTATUS.STALLRQ0)
• Transmit Stall 1 bit in the Endpoint Status register (EPSTATUS.STALLRQ1)
• Endpoint Interrupt Summary (EPINTSMRY) register
• Upstream resume bit in the Control B register (CTRLB.UPRSM)
At the end of the reset process, the End of Reset bit is set in the Interrupt Flag register
(INTFLAG.EORST).
38.6.2.5 Start-of-Frame
When a Start-of-Frame (SOF) token is detected, the frame number from the token is stored in the Frame
Number field in the Device Frame Number register (FNUM.FNUM), and the Start-of-Frame interrupt bit in
the Device Interrupt Flag register (INTFLAG.SOF) is set. If there is a CRC or bit-stuff error, the Frame
Number Error status flag (FNUM.FNCERR) in the FNUM register is set.
38.6.2.6 Management of SETUP Transactions
When a SETUP token is detected and the device address of the token packet does not match
DADD.DADD, the packet is discarded and the USB module returns to idle and waits for the next token
packet.
When the address matches, the USB module checks if the endpoint is enabled in EPCFG. If the
addressed endpoint is disabled, the packet is discarded and the USB module returns to idle and waits for
the next token packet.
When the endpoint is enabled, the USB module then checks on the EPCFG of the addressed endpoint. If
the EPCFG.EPTYPE0 is not set to control, the USB module returns to idle and waits for the next token
packet.
When the EPCFG.EPTYPE0 matches, the USB module then fetches the Data Buffer Address (ADDR)
from the addressed endpoint's descriptor and waits for a DATA0 packet. If a PID error or any other PID
than DATA0 is detected, the USB module returns to idle and waits for the next token packet.
SAM D5x/E5x Family Data Sheet
USB – Universal Serial Bus
© 2019 Microchip Technology Inc.
Datasheet
DS60001507E-page 1115