39.6.2.2 Endpoint Configuration

Endpoint data can be placed anywhere in the device RAM. The USB controller accesses these endpoints directly through the AHB master (built-in DMA) with the help of the endpoint descriptors. The base address of the endpoint descriptors needs to be written in the Descriptor Address register (DESCADD) by the user. Refer also to the Endpoint Descriptor structure in Endpoint Descriptor Structure.

Before using an endpoint, the user should configure the direction and type of the endpoint in Type of Endpoint field in the Device Endpoint Configuration register (EPCFG.EPTYPE0/1). The endpoint descriptor registers should be initialized to known values before using the endpoint, so that the USB controller does not read random values from the RAM.

The Endpoint Size field in the Packet Size register (PCKSIZE.SIZE) should be configured as per the size reported to the host for that endpoint. The Address of Data Buffer register (ADDR) should be set to the data buffer used for endpoint transfers.

The RAM Access Interrupt bit in Device Interrupt Flag register (INTFLAG.RAMACER) is set when a RAM access underflow error occurs during IN data stage.

When an endpoint is disabled, the following registers are cleared for that endpoint:

• 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)