SDR104 issue for MIMX8ML8CVNKZAB

[andrew_chen]

I am using a custom board with MIMX8ML8CVNKZAB and 88W8997  (radio chip) through SDIO bus.

1. The CPU s/w package are based on : i.mx 5.4.70 2.3.2
2. The system can bring up, access to AP and execute ping.
3. When running Iperf, the bus will drop and debug message are shown in below.

64 bytes from 192.168.101.128: seq=21 ttl=64 time=6.243 ms
64 bytes from 192.168.101.128: seq=22 ttl=64 time=2.466 ms
64 bytes from 192.168.101.128: seq=23 ttl=64 time=7.618 ms
64 bytes from 192.168.101.128: seq=24 ttl=64 time=8.964 ms
64 bytes from 192.168.101.128: seq=25 ttl=64 time=9.195 ms
64 bytes from 192.168.101.128: seq=26 ttl=64 time=4.030 ms
64 bytes from 192.168.101.128: seq=27 ttl=64 time=2.283 ms
64 bytes from 192.168.101.128: seq=28 ttl=64 time=2.341 ms
64 bytes from 192.168.101.128: seq=29 ttl=64 time=6.807 ms
^C
--- 192.168.101.128 ping statistics ---
30 packets transmitted, 30 packets received, 0% packet loss
round-trip min/avg/max = 1.719/4.807/10.931 ms
root@imx8mp-turbosom:~# iperf3 -c 192.168.101.128 -t 5000
Connecting to host 192.168.101.128, port 5201
[ 5] local 192.168.101.15 port 35600 connected to 192.168.101.128 port 5201
[ ID] Interval Transfer Bitrate Retr Cwnd
[ 5] 0.00-1.00 sec 14.2 MBytes 119 Mbits/sec 0 590 KBytes
[ 5] 1.00-2.00 sec 11.2 MBytes 94.3 Mbits/sec 2 486 KBytes
[ 5] 2.00-3.00 sec 11.2 MBytes 94.4 Mbits/sec 0 530 KBytes
[ 5] 3.00-4.00 sec 11.2 MBytes 94.4 Mbits/sec 0 559 KBytes
[ 5] 4.00-5.00 sec 11.2 MBytes 94.4 Mbits/sec 0 574 KBytes
[ 5] 5.00-6.00 sec 11.2 MBytes 94.4 Mbits/sec 0 581 KBytes
[ 5] 6.00-7.00 sec 11.2 MBytes 94.4 Mbits/sec 0 583 KBytes
[ 5] 7.00-8.00 sec 11.2 MBytes 94.4 Mbits/sec 0 583 KBytes
[ 5] 8.00-9.00 sec 11.2 MBytes 94.4 Mbits/sec 0 590 KBytes
[ 5] 9.00-10.00 sec 11.2 MBytes 94.4 Mbits/sec 0 604 KBytes
[ 5] 10.00-11.00 sec 11.2 MBytes 94.4 Mbits/sec 0 618 KBytes
[ 5] 11.00-12.00 sec 11.2 MBytes 94.4 Mbits/sec 0 632 KBytes
[ 5] 12.00-13.00 sec 11.2 MBytes 94.4 Mbits/sec 0 673 KBytes
[ 86.186206] ieee80211 phy0: mwl_read_data_sync : sdio_readsb buffer ptr = 0x000000001a2bcb37 ioport: 0x0 for size 256 failed with error -84
[ 86.198865] ieee80211 phy0: read mp_regs failed
[ 5] 13.00-14.00 sec 3.75 MBytes 31.4 Mbits/sec 1 1.41 KBytes
[ 5] 14.00-15.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 15.00-16.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 16.00-17.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes

Some test we have done:

• SDIO trace impedance measurement.--------impedance is controlled at 50+/-6 ohm up to 1GHz.
• SDIO trace length is about 14mm with trace difference less than 0.125mm.

• SDIO Clock /CMD/DATA  measurement from scope with active probe up to 5GHz BW

(a) below are the SDIO_CLK

(b) Below are the SDIO_DATA.

(c)CMD/CLK/DATA when running iperf

What is the issue when running Iperf? And any more data need to be captured in order to solve this?

Thanks

Andrew Chen

[igorpadykov]

Hi Andrew

for that issue one can try to change drive strength of SD signals using IOMUX PAD Control Register

IOMUXC_SW_PAD_CTL_PAD_x, also pay attention to power supplies ripples, allowable values

are given in   i.MX 8M Plus Hardware Developer’s Guide

Best regards
igor

[andrew_chen]

Hi Igor,

In the I.MX s/w package ( 5.4.70 2.3.2), it has higher driving level setting for SDR104. We have tried different driving level setting and it seems has no improvement.

Also, in our design (SCH attached), we can switch the interface to PCIe. The system run normally when we switch to PCIe. FYI.

Anything that I can try or you see anything wrong from my attached measure data?

Thanks

Andrew Chen

[igorpadykov]

Hi Andrew 

>Anything that I can try or you see anything wrong from my attached measure data?

I believe nothing. One can try to debug it, use for example AN4553 Using Open Source

Debugging Tools for Linux on i.MX Processors
https://www.nxp.com/docs/en/application-note/AN4553.pdf

Best regards
igor