I want to control chipselect for my spidevice from user space. i am using imax25 board.

priti1z — Wed, 08 Aug 2012 07:39:34 GMT

I have a requirement for control chipselect for my spidevice.

The requirement is between two writes or reads my device should remain selected from contoller.

For example the sequence is like :

Write opreation

1)chip select

2)send some data ( i am using ioctl(SPI_IOC_MESSAGE(1) )

3)send some more data ( means sending one more time ioctl command).

4)chip deselect

Now after Write operation i need to read the data.

Read Operation

1)chip select

2)Read data ( i am using ioctl(SPI_IOC_MESSAGE(1) )

3)Read more data ( means sending one more time ioctl command).

4)chip deselect

but as per my understanding whenever we call ioctl(SPI_IOC_MESSAGE(1)) the control finally goes to mxc_spi.c (which is controller driver) and for each write/read it selects the chip -> enables the clock -> write/read data then deselects the chip.

Note : i saw it wrtites to the control register which actually has the value for chip select and all.

Is there any way i can meet the above requirement?

i am really stuck.

Re: I want to control chipselect for my spidevice from user space. i am using imax25 board.

YS — Thu, 09 Aug 2012 20:52:30 GMT

SPI_IOC_MESSAGE can execute multiple read/write operations in single ioctl() request.

struct spi_ioc_transfer have member cs_change, which specifies if you want to deactivate CS between request or keep activated.

        unsigned char           cmd_buf[4];
        unsigned char           data_buf[8];
        struct spi_ioc_transfer xfer[2];

/* You must set command sequence on cmd_buf */

        xfer[0].tx_buf = (__u64) cmd_buf;
        xfer[0].len = 4; /* Length of command to write*/
        xfer[0].cs_change = 0; /* Keep CS activated */

        xfer[1].rx_buf = (__u64) data_buf;
        xfer[1].len = 8; /* Length of Data to read */
        xfer[1].cs_change = 0;

ioctl(fd, SPI_IOC_MESSAGE(2), xfer);

It worked on iMX28 at least.

i.MX ProcessorsのトピックRe: I want to control chipselect for my spidevice from user space. i am using imax25 board.

I want to control chipselect for my spidevice from user space. i am using imax25 board.

Re: I want to control chipselect for my spidevice from user space. i am using imax25 board.