I2C on Atlas-SoC via LTC pins

Hi all,

I am attempting to interface a 3.3V I2C-controlled video decoder with my Atlas-SoC board using the LTC 2x7 header pins; the SDA/SCK pins are pulled high to 3.3V via 2.2k resistors on the decoder board. It is my understanding that I should use pins 9 and 11 for SDA and SCK, as shown from the schematic on the System CD:

I also am assuming these pins are recognized by /dev/i2c-1, as that seems to be the bus giving me problems.

I can verify that the onboard IMU (0x53) on Bus 0 is recognized via I2C by running:

i2cdetect -r 0
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: – -- – -- – -- – -- – -- – -- –
10: – -- – -- – -- – -- – -- – -- – -- – --
20: – -- – -- – -- – -- – -- – -- – -- – --
30: – -- – -- – -- – -- – -- – -- – -- – --
40: – -- – -- – -- – -- – -- – -- – -- – --
50: – -- – 53 – -- – -- – -- – -- – -- – --
60: – -- – -- – -- – -- – -- – -- – -- – --
70: – -- – -- – -- – --

When I run i2cdetect -r 1, I get one of three possible outcomes. With no external hardware connected, it will usually just read back the individual address numbers:

 0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f

00: – 04 05 06 – 08 09 0a 0b 0c – 0e –
10: 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f
20: 20 21 – 23 24 25 26 27 28 29 2a 2b 2c 2d 2e 2f
30: – 31 32 33 34 35 36 37 38 39 3a – 3c 3d 3e 3f
40: 40 41 42 43 44 45 46 47 48 49 4a 4b – 4d 4e 4f
50: 50 51 52 53 – 55 56 57 58 59 5a 5b – 5d 5e 5f
60: 60 61 62 63 64 65 66 67 68 69 – 6b 6c 6d 6e 6f
70: 70 71 – 73 74 75 – 77

But, once I connect my other device’s SDA/SCK pins, which are pulled high to 3.3V via 2.2k resistors, I will get one of two responses for all address spaces (only first line copied for brevity):

 0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f

00: i2c_designware ffc05000.i2c: controller timed out

OR,

 0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f

00: i2c_designware ffc05000.i2c: i2c_dw_handle_tx_abort: lost arbitration

I’m not sure what else to try. I noticed there is a TS3A5018 MUX, U2, to select between either I2C or SPI lines, but tying the select pin (Pin 1) to 3.3V didn’t help either.

Any advice?

Best,
Ethan