Deserial Serial Peripheral Interface (DSPI)
Freescale Semiconductor
25-65
PXR40 Microcontroller Reference Manual, Rev. 1
25.5.4
Calculation of FIFO Pointer Addresses
The user has complete visibility of the TX and RX FIFO contents through the FIFO registers, and valid
entries can be identified through a memory mapped pointer and a memory mapped counter for each FIFO.
The pointer to the first-in entry in each FIFO is memory mapped. For the TX FIFO the first-in pointer is
the Transmit Next Pointer (TXNXTPTR). For the RX FIFO the first-in pointer is the Pop Next Pointer
(POPNXTPTR).
illustrates the concept of first-in and last-in FIFO entries along with the
FIFO Counter. The TX FIFO is chosen for the illustration, but the concepts carry over to the RX FIFO.
See
Section 25.4.3.4, Transmit First In First Out (TX FIFO) Buffering Mechanism
Receive First In First Out (RX FIFO) Buffering Mechanism
, for details on the FIFO operation.
Table 25-37. Delay Values
Delay Prescaler Values
1
3
5
7
Dela
y Scaler
V
a
lues
2
20.0 ns
60.0 ns
100.0 ns
140.0 ns
4
40.0 ns
120.0 ns
200.0 ns
280.0 ns
8
80.0 ns
240.0 ns
400.0 ns
560.0 ns
16
160.0 ns
480.0 ns
800.0 ns
1.1
s
32
320.0 ns
960.0 ns
1.6
s
2.2
s
64
640.0 ns
1.9
s
3.2
s
4.5
s
128
1.3
s
3.8
s
6.4
s
9.0
s
256
2.6
s
7.7
s
12.8
s
17.9
s
512
5.1
s
15.4
s
25.6
s
35.8
s
1024
10.2
s
30.7
s
51.2
s
71.7
s
2048
20.5
s
61.4
s
102.4
s
143.4
s
4096
41.0
s
122.9
s
204.8
s
286.7
s
8192
81.9
s
245.8
s
409.6
s
573.4
s
16384
163.8
s
491.5
s
819.2
s
1.1 ms
32768
327.7
s
983.0
s
1.6 ms
2.3 ms
65536
655.4
s
2.0 ms
3.3 ms
4.6 ms
Summary of Contents for PXR4030
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