CM108B recognition issue and infor missing issue

T
Tiger.luo
#1
2021/08/10 16:34

We met 2 problems with CM108B

  • After power ON/OFF for many times, the gateway can not recognize the USB device.
    • USB DP has a 1.5k pull up in our design. USB DM is also high during power ON.
    • When I add a 1.5k pull down to USB DM , USB DM goes to low during power ON. Then the device can be recognized. Why does this happen?
  • When the device is recognized by the gateway. The information from USB device is not correct for the 1st time. Some data is missing. And the data is complete at the 2nd time.

Gateway information :

  • H38WL using Allwinner H3: Linux 3.4 ;
  • H80WL using Allwinner H6 :Linux 3.10;
  • Orangepi Lite H6 is the same, using Linux 4.9
4 Replies
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2021/08/11
18:12
Last Reply
J
CM-Jack Chiu
#2
2021/08/10 17:42

Hi Tiger.luo:

CM108B IC has built-in 1.5k ohm pull-up, please remove the external 1.5k ohm and test again.

Thanks & B.R.

Jack

T
Tiger.luo
#3
2021/08/10 18:42

Dear Jack:

      OK. I will remove the 1.5K resisitor and try again.       But why an aditional  1.5K resisitor on DP can pullup the DM?

J
CM-Jack Chiu
#4
2021/08/11 09:35

Hi Tiger.luo:

According to the USB specification, the Full Speed device must have a pull-up 1.5k ohm on DP, and DM does not need to do any actions on the circuit. "DM pull down" does not meet USB specification, we can't predict what will happen. Thanks.

Jack

T
Tiger.luo
#5
2021/08/11 18:12

Dear Jack:

   Thanks for reminding. We are doing the test now ( without pullup and pulldown on DP & DM, use CM108B internal pullup )

   Could you please help us analysis the data missing issue?  18 bytes data only got 8 bytes. When 1st time send the command " Get Descriptor" ,we can not get full data. Please see JPG for detail.

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