Datasheet

ManualsBrandsMicrochip ManualsARM MicrocontrollersARM® Cortex® M0+ SAM Microcontroller 32bit 256KB TQFP

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The application software provides the size and address of the RAM buffer to be proceeded by the USB

module for a specific endpoint, and the USB module will split the buffer in the required USB data transfers

without any software intervention.

Figure 32-3. 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

32.6.2.4 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).

32.6.2.5 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.

32.6.2.6 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.

SAM D21 Family

USB – Universal Serial Bus

Datasheet Complete

DS40001882D-page 797