[#4669] WIFI USB tanges don't fully work on BF548-EZKIT and BF527-EZKIT
Submitted By: Bryan Wu
2008-11-25 04:49:07 Close Date
Closed Fixed In Release:
Found In Release:
BF548 Silicon Revision:
Is this bug repeatable?:
Uboot version or rev.:
Toolchain version or rev.:
App binary format:
Summary: WIFI USB tanges don't fully work on BF548-EZKIT and BF527-EZKIT
Michael did some test:
None of them really worked on the BF548-EZKIT MUSB Port!
2 of them don't even get enumerated.
However I found that these two work on a CM-BF527 Module from
Bluetechnix without problems, but also fail on a BF527-EZKIT, using the
same BF527 silicon revision !!!
I think we have some HW problems on our EZKIT boards.
The 3'rd one get's always enumerated however the ZyDAS driver is written
in a manor that it generates unaligned exceptions all over the place.
Also reported by Omar:
When I got the WIFI USB tangle, I will do some debugging.
--- Bryan Wu 2009-02-09 02:03:33
Wait for hardware guys updates, it should be workaround in hardware, IMO.
--- Bryan Wu 2009-02-13 01:06:52
The root cause of this issue was found by Michael. In the future, we will have a
hardware workaround to fix this issue:
I figured out the USB Enumeration issues seen with some USB Gadgets on EZKITs.
The problem is that the VBUS Voltage drops below 4.40 Volt during device
Causing a Blackfin USB VBUS_ERROR and the device on the other end of the line
See attached scope captures.
The voltage drop is due to missing capacitance on the VBUS supply as well due
to some resistance from the LDO and FET switch.
A simple 100uF Low ESR across VBUS fixes the problems.
There are three use cases we need to consider:
1) USB Host
From the USB 2.0 Spec:
126.96.36.199 Inrush Current Limiting
The hub downstream facing port VBUS power lines must be bypassed (CHPB) with no
less than 120 uF of low-ESR capacitance per hub. Standard bypass methods should
be used to minimize inductance and resistance between the bypass capacitors and
the connectors to reduce droop. The bypass capacitors themselves should have a
low dissipation factor to allow decoupling at higher frequencies.
2) USB Device (Cap should not be higher than 10uF)
The maximum load (CRPB) that can be placed at the downstream end of a cable is
10 uF in parallel with 44 OHM. The 10 uF capacitance represents any bypass
capacitor directly connected across the VBUS lines in the function plus any
capacitive effects visible through the regulator in the device. The 44 OHM
resistance represents one unit load of current drawn by the device during
3) USB OTG
(Cap should be in the range between 1uF and 10uF)
Please refer to USB Engineering Change Notice: ECN Device Capacitance
This leads to the requirement that the 100uF+ should be switchable, by a
The whole thing is kind of a common problem with OTG Ports.
See this link below:
DaVinci and OMAP (BTW featuring the same Mentor USB IP) Evaluation boards
suffer the same problem.
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