CODEWITHSUNDEEP
linuxembedded-linuxspi
Hesham.K
Hesham.K

Reputation: 49

How to set chip select in SPI programming for multipleslaves ? (struct spi_ioc_transfer)

Maybe I am asking the wrong question actually but I am just making my first steps in the embedded world. So I am sorry if the question is somehow stupid.

I am trying to program a software for 9DOF IMU in c++ and linux environment.

As far as I understood the SPI, the SS pin has to be low active in order for a transmission to occur. I have seen multiple reading or writing bytes function examples and all using the struct spi_ioc_transfer but they were all single slave examples and there is no mention about setting or configuring the SS in the code. Also When I check the structre of spi_ioc_transfer there is the cs_change however, how does it know which cs we are dealing with from the beginning ?

Upvotes: 1

Views: 2801

Answers (1)

Wocket
Wocket

Reputation: 250

The chip select (CS or SS) to use is determined by which device node you open.

To talk to a SPI chip with the Linux spidev driver, you open a device such as /dev/spidev0.1. The numbers in the device node file name refer to the bus and chip select, respectively — in this example it would be the first bus (0) and the second CS (1). If you want to talk to devices on different chip-selects, you have to open different device nodes and do ioctls on the appropriate one.

Upvotes: 2

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