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)
Hi jongju
one can consult with datasheet connected device if it supports 20Mhz
and check with oscilloscope timings using sect.4.12.2.1 ECSPI Master Mode Timing
i.MX6DQ Datasheet
http://www.nxp.com/docs/en/data-sheet/IMX6DQCEC.pdf
Best regards
igor
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