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DMA Serial Peripheral Interface (DSPI)
Freescale Semiconductor
31-41
Figure 31-24. TX FIFO Pointers and Counter
31.5.5.1
Address Calculation for the First-in and Last-in Entries in the TX FIFO
The memory address of the first-in entry in the TX FIFO is computed by the following equation:
First-in entry address = TXFIFO base + 4
(TXNXTPTR)
The memory address of the last-in entry in the TX FIFO is computed by the following equation:
Last-in entry address = TX FIFO base + 4
[(TXCTR + TXNXTPTR - 1) modulo TX FIFO depth]
where:
TX FIFO base: base address of TX FIFO
TXCTR: TX FIFO counter
TXNXTPTR: transmit next pointer
TX FIFO depth: 16
31.5.5.2
Address Calculation for the First-in and Last-in Entries in the RX FIFO
The memory address of the first-in entry in the RX FIFO is computed by the following equation:
First-in entry address = RX FIFO base + 4
(POPNXTPTR)
The memory address of the last-in entry in the RX FIFO is computed by the following equation:
Last-in entry address = RX FIFO base + 4
[(RXCTR + POPNXTPTR - 1) modulo RX FIFO
depth]
RX FIFO base: base address of RX FIFO
RXCTR: RX FIFO counter
POPNXTPTR: pop next pointer
RX FIFO depth: 16
Entry C
Entry A (First In)
– 1
Entry B
Entry D (Last In)
TX FIFO Base
Push TX FIFO
TX FIFO Counter
Shift Register
DSPI_SOUT
Register
Transmit Next
Data Pointer
–
–
–
–
+ 1
(TXNXTPTR)
Содержание MCF54455
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