Figure 21-5: Interrupt Generation without Programmable THRE Interrupt Mode
THRE
Interrupt
Enabled?
TX FIFO
Empty?
yes
no
Clear INTR
yes
no
Set INTR
(INTR Is Asserted If
There Are No Interrupts)
TX FIFO Not
Empty?
yes
no
UART Controller Programming Model
DMA Controller Operation
The UART controller includes a DMA controller interface to indicate when the receive FIFO buffer data is
available or when the transmit FIFO buffer requires data. The DMA requires two channels, one for transmit
and one for receive. The UART controller supports both single and burst transfers.
The FIFO buffer depth (
FIFO_DEPTH
) for both the RX and TX buffers in the UART controller is 128
entries.
Related Information
on page 16-1
For more information, refer to this
DMA Controller
chapter.
Transmit FIFO Underflow
During UART serial transfers, transmit FIFO requests are made to the DMA controller whenever the number
of entries in the transmit FIFO is less than or equal to the decoded level of the Transmit Empty Trigger
(
TET
) field in the FIFO Control Register (
IIR_FCR
), also known as the watermark level. The DMA controller
responds by writing a burst of data to the transmit FIFO buffer, of length specified as DMA burst length. †
Altera Corporation
UART Controller
21-7
UART Controller Programming Model
cv_54021
2013.12.30