SPRUIV7B May 2022 – September 2023 AM620-Q1 , AM623 , AM625 , AM625-Q1 , AM625SIP
In FIFO interrupt mode (the FIFO control register UART_FCR[0] FIFO_EN bit is set to 1 and relevant interrupts are enabled by the UART_IER_UART 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 UART_TLR[7-4] RX_FIFO_TRIG_DMA and UART_TLR[3-0] TX_FIFO_TRIG_DMA bit fields or the UART_FCR[7-6] RX_FIFO_TRIG and UART_FCR[5-4] TX_FIFO_TRIG bit fields, respectively) is reached.
The interrupt signals instruct the Host CPU 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 UART_TCR[3-0] RX_FIFO_TRIG_HALT bit field) must be greater than or equal to the RX FIFO threshold.
Figure 12-111 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 Host CPU 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 12-112 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.