38.6.2.12 Management of IN Endpoints

Overview

IN packets are sent by the USB device controller upon IN requests from the host. All data which acknowledges or not the bank can be written when it is full.

The endpoint must be configured first.

The USBHS_DEVEPTISRx.TXINI bit is set at the same time as USBHS_DEVEPTIMRx.FIFOCON when the current bank is free. This triggers a PEP_x interrupt if the Transmitted IN Data Interrupt Enable (USBHS_DEVEPTIMRx.TXINE) bit is one.

USBHS_DEVEPTISRx.TXINI is cleared by software (by writing a one to the Transmitted IN Data Interrupt Clear bit (USBHS_DEVEPTIDRx.TXINIC) to acknowledge the interrupt, which has no effect on the endpoint FIFO.

The user then writes into the FIFO and writes a one to the FIFO Control Clear (USBHS_DEVEPTIDRx.FIFOCONC) bit to clear the USBHS_DEVEPTIMRx.FIFOCON bit. This allows the USBHS to send the data. If the IN endpoint is composed of multiple banks, this also switches to the next bank. The USBHS_DEVEPTISRx.TXINI and USBHS_DEVEPTIMRx.FIFOCON bits are updated in accordance with the status of the next bank.

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

The USBHS_DEVEPTISRx.RWALL bit is set when the current bank is not full, i.e., when the software can write further data into the FIFO.

Figure 38-11. Example of an IN Endpoint with one Data Bank

Figure 38-12. Example of an IN Endpoint with two Data Banks

The data is written as follows:

When the bank is empty, USBHS_DEVEPTISRx.TXINI and USBHS_DEVEPTIMRx.FIFOCON are set, which triggers a PEP_x interrupt if USBHS_DEVEPTIMRx.TXINE = 1.
The user acknowledges the interrupt by clearing USBHS_DEVEPTISRx.TXINI.
The user writes the data into the current bank by using the USB Pipe/Endpoint nFIFO Data (USBFIFOnDATA) register, until all the data frame is written or the bank is full (in which case USBHS_DEVEPTISRx.RWALL is cleared and the Byte Count (USBHS_DEVEPTISRx.BYCT) field reaches the endpoint size).
The user allows the controller to send 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 written while the previous one is being read by the host. Then, when the user clears USBHS_DEVEPTIMRx.FIFOCON, the following bank may already be free and USBHS_DEVEPTISRx.TXINI is set immediately.

An “Abort” stage can be produced when a zero-length OUT packet is received during an IN stage of a control or isochronous IN transaction. The Kill IN Bank (USBHS_DEVEPTIMRx.KILLBK) bit is used to kill the last written bank. The best way to manage this abort is to apply the algorithm represented in the following figure.