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Why? Is SPI a problem at high speed?

Question asked by jongju park on Aug 22, 2018
Latest reply on Aug 23, 2018 by jongju park

Dear community,

 

**Question**
Is SPI a problem at high speed?
 

**description**

1. Chip : MCIMX6Q5EYM10AD

2. Kernel Version : L3.14.28

 

I have tested 20Mhz from 10Mhz with SPI Master Mode between iMX6Q and SPI device.

I simply tested the memory of the SPI device to read it.
Up to 10Mhz ~ 14Mhz worked normally.
However, since 15Mhz, there is a problem with the data.

 

▣ SPI communication result according to frequency

MHz

Result

Read Data

10

OK

0x92520001

11

OK

0x92520001

12

OK

0x92520001

13

OK

0x92520001

14

OK

0x92520001

15

FAIL

0xc9290000

16

FAIL

0xc9290000

17

FAIL

0xc9290000

18

FAIL

0xc9290000

19

FAIL

0xc9290000

20

FAIL

0xc9290000

 

The difference between the normal data (0x92520001) and the abnormal data (0xc9290000)
Moving the least significant bit of normal data forward is exactly like abnormal data. This seems to be a bug in the SPI driver.

 

▣ Datas comparison

 

Hex

Bit

0x92520001

1001 0010 0101 0010 0000 0000 0000 0001 <--- least significant bit

0xc9290000

1100 1001 0010 1001 0000 0000 0000 0000

 

1001 0010 0101 0010 0000 0000 0000 0001 (0x92520001)

11001 0010 0101 0010 0000 0000 0000 000

1100 1001 0010 1001 0000 0000 0000 0000 (0xc9290000)

 

 

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