iMX6 SPI Read Timing Issue

[narasimma2]

Hi I'm using iMX6 Quad with Linux Kernel 3.14.38, i'm trying to read data from ADC chip through SPI interface, i'm having the throughput issue, so when i probed on the scope each SPI read takes more than 70 microseconds, but our requirement is read 128bit data less than 20 microseconds.

Find the attached Timing snapshot between SCLK and Chip Select.

It consumes more time on following operations,

• SPI Read call to CS Low
• CS Low to First SCLK
• Last SCLK to CS High
• CS High to SPI Read call finished 

Please help me to resolve this issue.

[igorpadykov]

Hi Narasimma

for increasing performance one can try to use bursts,

please look at BURST_LENGTH description in

sect.20.7.3 Control Register (ECSPIx_CONREG) i.MX6UL Reference Manual

http://www.nxp.com/docs/en/reference-manual/IMX6ULRM.pdf

Best regards
igor
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[narasimma2]

Hi igor,

Thanks for reply,

We tried changing BURST_LENGTH to 128 bits. But IMX SPI driver is restricting it to 32 bits & it doesn't solve our issue. Our primary issue is that even for 8-bit BURST_LENGTH, we are not getting typical SPI Burst as per Figure 20-4 (page-776) in Ref Manual : http://www.nxp.com/docs/en/reference-manual/IMX6ULRM.pdf. Please refer our attached snapshot and help us in resolving why we are facing delay in uSecs between SCLK & CS signals.