10-10 Intel® PXA255 Processor Developer’s Manual

UARTs

In FIFO mode, the “Received Data is available” interrupt (Priority Level 2) takes priority over the

“Character Timeout Indication” interrupt (Priority Level 2). For example, if the UART is in FIFO

mode and FIFO Control Register[ITL] = 0b00, this will cause the UART to generate an interrupt

when there is one byte in the FIFO. In this scenario, if ther e is one byte in the FIFO, an interrupt is

generated, and IIR[3:0] = 0b0100, which indicates that Recei ved Data is available. If data remains

in the FIFO and if a Character Timeout occurs (no data has been sent for 4 character times), then

the interrupt status does not change to IIR[3:0] = 0b1100 (Character Timeout Indication).

The error interrupt is repor ted separately in the LSR. In DM A mode, software must check for the error interrupt before it checks the IIR. If additional data is received before a Character Timeout Indication interrupt is serviced, th e interrupt is deasserted.This is a read-onl y register. Ignore reads f rom reserved bits.Table 10-8. Interrupt Conditions
Priority Level Interrupt origin
1 (highest) Receiver Line Status: one or more error bits were set.
2Received Data is available. In FIFO mode, trigger level was reached. In
non-FIFO mode, RBR has data.
2Character Timeout Indication occurred. Occurs only in FIFO mode, when
data is in the receive FIFO but no data has been sent for a set time period.
3Transmitter requests data. In FIFO mode, the transmit FIFO is at least half
empty. In non-FIFO mode, the THR has been transmitted.
4 (lowest) Modem Status: one or more modem input signal has changed state.
Table 10-9. IIR Bit Definitions (Sheet 1 of 2)
Base+0x8 Interrupt Identification Register UART
Bit 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
reserved
FIFOES1
FIFOES0
reserved
reserved
IID3
IID2
IID1
IP
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
Bits Name Description
31:8 — reserved
7:6 FIFOES[1:0]
FIFO Mode Enable Status:
00 – Non-FIFO mode is selected
01 – reserved
10 – reserved
11 – FIFO mode is selected (FCR[TRFIFOE] = 1)
5:4 — res erved