Management of OUT Endpoints

Overview

OUT packets are sent by the host. All data which acknowledges or not the bank can be read when it is empty.

The endpoint must be configured first.

The USBHS_DEVEPTISRx.RXOUTI bit is set at the same time as USBHS_DEVEPTIMRx.FIFOCON when the current bank is full. This triggers a PEP_x interrupt if the Received OUT Data Interrupt Enable (USBHS_DEVEPTIMRx.RXOUTE) bit is one.

USBHS_DEVEPTISRx.RXOUTI is cleared by software (by writing a one to the Received OUT Data Interrupt Clear (USBHS_DEVEPTICRx.RXOUTIC) bit to acknowledge the interrupt, which has no effect on the endpoint FIFO.

The user then reads from the FIFO and clears the USBHS_DEVEPTIMRx.FIFOCON bit to free the bank. If the OUT endpoint is composed of multiple banks, this also switches to the next bank. The USBHS_DEVEPTISRx.RXOUTI and USBHS_DEVEPTIMRx.FIFOCON bits are updated in accordance with the status of the next bank.

USBHS_DEVEPTISRx.RXOUTI is always cleared before clearing USBHS_DEVEPTIMRx.FIFOCON.

The USBHS_DEVEPTISRx.RWALL bit is set when the current bank is not empty, i.e., when the software can read further data from the FIFO.

Figure 1. Example of an OUT Endpoint with one Data Bank

Figure 2. Example of an OUT Endpoint with two Data Banks

Detailed Description

The data is read as follows:

When the bank is full, USBHS_DEVEPTISRx.RXOUTI and USBHS_DEVEPTIMRx.FIFOCON are set, which triggers a PEP_x interrupt if USBHS_DEVEPTIMRx.RXOUTE = 1.
The user acknowledges the interrupt by writing a one to USBHS_DEVEPTICRx.RXOUTIC in order to clear USBHS_DEVEPTISRx.RXOUTI.
The user can read the byte count of the current bank from USBHS_DEVEPTISRx.BYCT to know how many bytes to read, rather than polling USBHS_DEVEPTISRx.RWALL.
The user reads the data from the current bank by using the USBFIFOnDATA register, until all the expected data frame is read or the bank is empty (in which case USBHS_DEVEPTISRx.RWALL is cleared and USBHS_DEVEPTISRx.BYCT reaches zero).
The user frees the bank and switches to the next bank (if any) by clearing USBHS_DEVEPTIMRx.FIFOCON.

If the endpoint uses several banks, the current one can be read while the following one is being written by the host. Then, when the user clears USBHS_DEVEPTIMRx.FIFOCON, the following bank can already be read and USBHS_DEVEPTISRx.RXOUTI is set immediately.

In High-speed mode, the PING and NYET protocols are handled by the USBHS.

For a single bank, a NYET handshake is always sent to the host (on Bulk-out transaction) to indicate that the current packet is acknowledged but there is no room for the next one.
For a double bank, the USBHS responds to the OUT/DATA transaction with an ACK handshake when the endpoint accepted the data successfully and has room for another data payload (the second bank is free).