SPI Read Not Working

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SPI Read Not Working

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Contributor II

I use the i.mx sabreauto board to communicate to the other board with SPI interface.

But, I cannot get the data from SPI Interface. 

I use the oscilloscope to check the CLK signal, and the write operation can generate the CLK signal,

but the read one cannot.

Linux version is Linux version 4.1.15-1.1.1

CPU: ARMv7 Processor [412fc09a] revision 10 (ARMv7)

Please, give some hint about this issue. Thank you.

The test source and log is attached.

Original Attachment has been moved to: teraterm20190929182.log.zip

Original Attachment has been moved to: spitester.c.zip

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Contributor V

In 3-wire (clk, tx, rx) spi protocol a read is done during the write.

The read function (Chip_SSP_ReceiveFrame() or Chip_SPI_ReceiveFrame())call just returns the data that went in the fifo during the last write.

If you need to read after sending a command (reading spi flash for example ), you will need to write "dummy" data to clock out the data from the slave. Look at function (Chip_SSP_ReadFrames_Blocking() or Chip_SPI_ReadFrames_Blocking()) for reference.

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Contributor I

Fifo during the last write it's good way in this topic and the crucial thing how spi works

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Contributor V

In 3-wire (clk, tx, rx) spi protocol a read is done during the write.

The read function (Chip_SSP_ReceiveFrame() or Chip_SPI_ReceiveFrame())call just returns the data that went in the fifo during the last write.

If you need to read after sending a command (reading spi flash for example ), you will need to write "dummy" data to clock out the data from the slave. Look at function (Chip_SSP_ReadFrames_Blocking() or Chip_SPI_ReadFrames_Blocking()) for reference.

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Contributor II

Hi, Raymundo Velarde

Thank you for your answer.

I think your right. To Read the data from slave, I need sent the dummy data to slave.

I use the SPI_IOC_MESSAGE(1) , and fill the tx_buf with "0", then the clock is generated.

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NXP TechSupport
NXP TechSupport

Hi Jie

this is correct, in master mode processor generates clock during write,

please check Chapter 21 Enhanced Configurable SPI (ECSPI)

i.MX6DQ Reference Manual

http://cache.freescale.com/files/32bit/doc/ref_manual/IMX6DQRM.pdf

Spi test can be found in imx-test package (folder mxc_spi_test)

www.nxp.com/lgfiles/NMG/MAD/YOCTO/imx-test-5.4.tar.gz

Best regards
igor
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Contributor II

Hi igorpadykov,

Thank you for your answer.

I checked the document IMX6DQRM.pdf

21.4.4.1 Typical Master Mode

****
When the ECSPI is in Master mode the SS, SCLK, and MOSI are output signals, and the MISO signal is an input.

****

It means in Master mode When i use the READ command , the SCLK signals should be generated.

But in my case , the SCLK has no signals when i use the 

  retSize = read (fd, &data, sizeof(data));

I also run the imx-test package mxc_spi_test, and i get the error below:

./spitester_mxc -D 0 -s 1000000 -b 8 

Execute data transfer test: 0 1 8
spi mode: 0
bits per word: 8
max speed: 1000000 Hz (1000 KHz)
can't send spi messageCorrupted data at 0 wbuf = 56 rbuf = 0
Data sent : 8
Data received :
Test FAILED.

./spitester_mxc -D 0 -s 1000000 -b 8 0BFD01000000
Execute data transfer test: 0 12 0BFD01000000
spi mode: 0
bits per word: 8
max speed: 1000000 Hz (1000 KHz)
Corrupted data at 0 wbuf = 48 rbuf = 0
Corrupted data at 1 wbuf = 66 rbuf = 0
Corrupted data at 2 wbuf = 70 rbuf = 0
Corrupted data at 3 wbuf = 68 rbuf = 0
Corrupted data at 4 wbuf = 48 rbuf = 0
Corrupted data at 5 wbuf = 49 rbuf = 0
Corrupted data at 6 wbuf = 48 rbuf = 0
Corrupted data at 7 wbuf = 48 rbuf = 0
Corrupted data at 8 wbuf = 48 rbuf = 0
Corrupted data at 9 wbuf = 48 rbuf = 0
Corrupted data at 10 wbuf = 48 rbuf = 0
Corrupted data at 11 wbuf = 48 rbuf = 0
Data sent : 0BFD01000000
Data received :
Test FAILED.

I just want to send 6byte to the slave and there is 12Byte.

and the wbuf is corrupted.

pls help me to resolve this problem.

Thank you!

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NXP TechSupport
NXP TechSupport

Hi Jie

please check for example
http://www.corelis.com/education/SPI_Tutorial.htm
"Simple SPI Read Transaction" :

This sequence is really a single-byte write followed by a two byte read;

~igor

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Contributor II

Hi igorpadykov,

Thank you for your answer.

I checked the doc 

http://www.corelis.com/education/SPI_Tutorial.htm
"Simple SPI Read Transaction" 

But, I still think the driver(or hardware) is weird.

Because i use the same example spitester.c.zip i attached before,It works on raspberrypi.

Both of write/read operation and spi_ioc_massage(2)(read after write) operation can give the right response from slave device.

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