Texas Instruments OMAP5912 Reference Manual page 1249

UARTs
Figure 70. Receive FIFO IT Request Generation
Programmable flow control threshold
Programmable FIFO threshold
Figure 71. Transmit FIFO IT Request Generation
Transmit FIFO level
Programmable FIFO threshold
184 Serial Interfaces
Receive FIFO level
Zero byte
Interrupt request
In receive, no interrupt is generated until receive FIFO reaches its threshold.
Once low, the interrupt can only be deasserted when the local host has
handled enough bytes to make the FIFO level below threshold. The flow
control threshold is set at a higher value than FIFO threshold.
Full level
Number
of
spaces
Zero byte
Interrupt request
In transmit mode, an interrupt request is automatically asserted when FIFO is
empty. This request is deasserted when the FIFO crosses the threshold level.
The interrupt line is deasserted until a sufficient number of elements has been
transmitted to go below FIFO threshold.
LH acknowledged IT request
and transferred enough bytes to
recover FIFO level below
threshold
Interrupt request active low
Interrupt request
active low
Time
Time
Time
Time
SPRU760B