STR720 datasheet(193/401 Pages) STMICROELECTRONICS

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STR720 - BUFFERED SPI (BSPI)

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17.3.8

DMA Interface

The DMA interface is a feature of the BSPI that allows data to be transferred to or from system

memory using a DMA controller instead of main CPU. Data can be transferred in single data

accesses or in burst mode, the amount of words being selectable by the programmer, thus

making efficient more use of system bus. The BSPI DMA interface has the following features:

1) The DMA interface can be totally disabled using a bit in BSPCSR3 register.

2) User programmable burst size: 1, 4, 8 or 16 words can be transferred at a time.

3) Two request lines to the DMA are generated: one dedicated to the BSPI operating in

transmit mode and another dedicated to the BSPI operating in receive mode. These signals

are generated in independently from each other inside the BSPI.

4) Received 8-bit data, being sent from the BSPI to the memory, is arranged in a format which

is compatible both with little and big endian convention, replicating the received data on both

high and low byte in BSPRXR register.

The DMA interface makes use of pointers inside both the transmit and receive fifo (these

being independent of one another) in order for it to decide when a DMA request to transmit or

receive data can be made. The choice of burst size should match the one configured in the

corresponding DMA channel.

Note

There is a restriction on the burst capability of DMA interface during reception. The

total number of words to be transferred to system memory via DMA must be an

integer multiple of the programmed Burst Length size, since DMA interface is not

capable of handling incomplete received burst transfers. For example if Burst Length

size is set to 4 and at the end of received data transfer BSPI FIFO has only 3 spaces,

no request would be issued. On the contrary, with an even divide, the last chunk of

received data will always be equal to the programmed size of the burst length.

STR720 数据表(PDF) 193 Page - STMicroelectronics