[#4669] WIFI USB tanges don't fully work on BF548-EZKIT and BF527-EZKIT

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[#4669] WIFI USB tanges don't fully work on BF548-EZKIT and BF527-EZKIT

Submitted By: Bryan Wu

Open Date

2008-11-25 04:49:07     Close Date

2009-03-03 03:17:41

Priority:

Medium     Assignee:

Bryan Wu

Status:

Closed     Fixed In Release:

N/A

Found In Release:

N/A     Release:

Category:

N/A     Board:

N/A

Processor:

BF548     Silicon Revision:

Is this bug repeatable?:

Yes     Resolution:

Fixed

Uboot version or rev.:

    Toolchain version or rev.:

4.1

App binary format:

N/A     

Summary: WIFI USB tanges don't fully work on BF548-EZKIT and BF527-EZKIT

Details:

 

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:

  blackfin.uclinux.org/gf/project/uclinux-dist/forum/?action=ForumBrowse&_forum_action=MessageReply&message_id=65060

 

When I got the WIFI USB tangle, I will do some debugging.

-Bryan

 

Follow-ups

 

--- Bryan Wu                                                 2009-02-09 02:03:33

Wait for hardware guys updates, it should be workaround in hardware, IMO.

 

-Bryan

 

--- 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:

 

---

Hi Kevin,

 

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

initialization.

 

Causing a Blackfin USB VBUS_ERROR and the device on the other end of the line

to malfunction.

 

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:

 

7.2.4.1 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

connect.

 

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

jumper.

 

The whole thing is kind of a common problem with OTG Ports.

 

See this link below:

 

  wiki.davincidsp.com/index.php?title=USB_OTG_on_DaVinci

 

DaVinci and OMAP (BTW featuring the same Mentor USB IP) Evaluation boards

suffer the same problem.

 

Best regards,

 

Michael

---

 

Thanks

-Bryan

 

 

 

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