9.3.7.11.10 FIFO Thresholds

Each Transmit and Receive FIFO includes a threshold feature used to set a flag and an interrupt when a FIFO threshold is crossed. Thresholds are defined as a number of data in the FIFO, and the FIFO state (TXFL or RXFL) represents the number of data currently in the FIFO.

The Transmit FIFO threshold can be set using the field FLEX_US_FMR.TXFTHRES. Each time the Transmit FIFO level goes from ‘above threshold’ to ‘equal to or below threshold’, the flag FLEX_US_FESR.TXFTHF is set. The application is warned that the Transmit FIFO has reached the defined threshold and that it can be reloaded.

The Receive FIFO threshold can be set using the field FLEX_US_FMR.RXFTHRES. Each time the Receive FIFO level goes from ‘below threshold’ to ‘equal to or above threshold’, the flag FLEX_US_FESR.RXFTHF is set. The application is warned that the Receive FIFO has reached the defined threshold and that it can be read to prevent an underflow.

The Receive FIFO threshold 2 can be set using the field FLEX_US_FMR.RXFTHRES2. Each time the Receive FIFO level goes from ‘above threshold 2’ to ‘equal to or below threshold 2’, the flag FLEX_US_FESR.RXFTHF2 is set. The application is warned that the Receive FIFO has reached the defined threshold and that it can be read to prevent an underflow.

The TXFTHF, RXFTHF and RXTHF2 flags can be configured to generate an interrupt using FLEX_US_FIER and FLEX_US_FIDR.