39.6.3.4 Pipe Configuration
Pipe data can be placed anywhere in the RAM. The USB controller accesses these pipes directly through the AHB master (built-in DMA) with the help of the pipe descriptors. The base address of the pipe descriptors needs to be written in the Descriptor Address register (DESCADD) by the user. Refer also to Pipe Descriptor Structure.
Before using a pipe, the user should configure the direction and type of the pipe in Type of Pipe field in the Host Pipe Configuration register (PCFG.PTYPE). The pipe descriptor registers should be initialized to known values before using the pipe, so that the USB controller does not read the random values from the RAM.
The Pipe Size field in the Packet Size register (PCKSIZE.SIZE) should be configured as per the size reported by the device for the endpoint associated with this pipe. The Address of Data Buffer register (ADDR) should be set to the data buffer used for pipe transfers.
The Pipe Bank bit in PCFG (PCFG.BK) should be set to one if dual banking is desired. Dual bank is not supported for Control pipes.
The Ram Access Interrupt bit in Host Interrupt Flag register (INTFLAG.RAMACER) is set when a RAM access underflow error occurs during an OUT stage.
When a pipe is disabled, the following registers are cleared for that pipe:
- Interval for the Bulk-Out/Ping transaction register (BINTERVAL)
- Pipe Interrupt Enable Clear/Set register (PINTENCLR/SET)
- Pipe Interrupt Flag register (PINTFLAG)
- Pipe Freeze bit in Pipe Status register (PSTATUS.FREEZE)