11 scratchpad register (spr), Table 10-16. scratch pad register - spr, 3 fifo interrupt mode operation – Intel PXA26X User Manual
Page 387: 1 receive interrupt, 2 character timeout indication interrupt
Intel® PXA26x Processor Family Developer’s Manual
10-21
Universal Asynchronous Receiver/Transmitter
10.4.2.11
Scratchpad Register (SPR)
The read/write SPR has no effect on the UART. It is intended as a scratchpad register for use by the
programmer. It is included for 16550 compatibility.
10.4.3
FIFO Interrupt Mode Operation
This section describes how to service interrupts in FIFO mode.
10.4.3.1
Receive Interrupt
For a receive interrupt to occur, the receive FIFO and receive interrupts must be enabled. IIR[IID]
changes to show that receive data is available when the FIFO reaches its trigger level. IIR[IID]
changes to show the next waiting interrupt when the FIFO drops below the trigger level. A change
in IIR[IID] triggers an interrupt to the core. Software reads IIR[IID] to determine the cause of the
interrupt.
The receiver line status interrupt (IIR = 0xC6) has the highest priority. The received data available
interrupt (IIR = 0xC4) is lower. The line status interrupt occurs only when the character at the front
of the FIFO has errors.
The data ready bit (DR in the LSR) is set when a character is transferred from the shift register to
the receive FIFO. The DR bit is cleared when the FIFO is empty.
10.4.3.2
Character Timeout Indication Interrupt
A character timeout indication interrupt occurs when the receive FIFO and character timeout
indication interrupt are enabled and all of the following conditions exist:
•
At least one character is in the FIFO.
•
The most recently received character was received more than four continuous character times
ago. If two stop bits are programmed, the second is included in this interval.
•
The most recent FIFO read was performed more than four continuous character times ago.
Table 10-16. Scratch Pad Register
–
SPR
Base+0x1C
Scratch Pad 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
R
e
ser
ve
d
SP
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
0
Read/Write
Bits
Name
Description
31:8
—
Reserved
7:0
SP
SCRATCH PAD:
No effect on UART functionality