SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
In FIFO interrupt mode (the FIFO control register UARTi.UART_FCR[0] FIFO_EN bit is set to 1 and relevant interrupts are enabled by the UARTi.UART_IER register), an interrupt signal informs the processor of the status of the receiver and transmitter. These interrupts are raised when the RX/TX FIFO threshold (the UARTi.UART_TLR[7:4] RX_FIFO_TRIG_DMA and UARTi.UART_TLR[3:0] TX_FIFO_TRIG_DMA bit fields or the UARTi.UART_FCR[7:6] RX_FIFO_TRIG and UARTi.UART_FCR[5:4] TX_FIFO_TRIG bit fields, respectively) is reached.
The interrupt signals instruct the MPU to transfer data to the destination (from the UART in receive mode and/or from any source to the UART FIFO in transmit mode).
When UART flow control is enabled with interrupt capabilities, the UART flow control FIFO threshold (the UARTi.UART_TCR[3:0] RX_FIFO_TRIG_HALT bit field) must be greater than or equal to the RX FIFO threshold.
Figure 24-60 shows the generation of the RX FIFO interrupt request.
In receive mode, no interrupt is generated until the RX FIFO reaches its threshold. Once low, the interrupt can be deasserted only when the MPU has handled enough bytes to put the FIFO level below threshold. The flow control threshold is set at a higher value than the FIFO threshold.
Figure 24-61 shows the generation of the TX FIFO interrupt request.
In transmit mode, an interrupt request is automatically asserted when the TX FIFO is empty. This request is deasserted when the TX FIFO crosses the threshold level. The interrupt line is deasserted until a sufficient number of elements is transmitted to go below the TX FIFO threshold.