Disapearing pl2303 usb serial adapter on rpi2

[Hans Petter Selasky]

On 12/22/17 05:16, bob prohaska wrote:
> Hi Hans,
 >
>> Hi,
>>
>> You might want to run "usbdump" with the appropriate arguments to
>> capture all USB traffic during such a cycle.
>>
> I'll try it next time the pl2303 locks up.
> 
>> Further, you might want to only enable USB HUB debug messages to figure
>> out why the USB stack thinks the device is going away:
>>
>> sysctl hw.usb.uhub.debug=17
>>
> I've turned that on, and the console is spitting out a lot of output.
> It'll make quite a haystack in which to find a needle 8-) Any hint
> what to look for?
>

Hi,

You should look for a port change event reporting a change in the status 
bits which is non-zero.

>>   From what I know, the RPI series of cards have a small external USB HUB
>> on the board. All USB traffic goes through this High-Speed HUB. When you
>> are using LOW and FULL speed, all traffic is translated from High-Speed
>> USB into LOW and FULL speed USB.
>>
> 
> Would changing the baudrate have any effect? A console certainly needn't
> run at 115200 baud. For present purposes 9600 or less is plenty.
>> I don't rule out some kind of "bug" in this external piece of hardware.

No, doesn't have anything to do with the USB packets.

>>
> Many have said pl2303 devices are unreliable, but they seem well-behaved
> on a Mac and on an RPI3 running Raspbian. Whatever is wrong, it seems not
> deterministic, but cumulative, with a touch of random.
> 
>> You might also try to set (my wild guess):
>> sysctl hw.usb.no_cs_fail=1
>>
> Not sure I understand what this does; is there a description somewhere?

This is a recovery mechanism, which triggers if the device appears dead, 
that it will automatically re-enumerate the USB device. Setting this 
sysctl prevents that mechanism.

> 
>> Like already mentioned in this thread, the micro USB power input
>> connecter on the RPI is not supposed to handle more than 500mA,
>> regardless of how strong your power supply is. Then you need to subtract
>> the mA's used by the CPU and other chips like ethernet. I wouldn't be
>> surprised if ethernet functionality alone required 150mA at +5V.
>>
> Some time ago I put a voltmeter on the Pi and the voltage stayed over
> five volts, but of course short spikes weren't visible in such a test.
> On average, however, the connector seemed to handle the load.
I think the USB specification mandates that the voltage must stay 
exactly within certain limits ... I don't remember all the details at 
the moment, but I think the USB 2.0 specification from usb.org will 
mention this.

> 
>> USB LOW/HIGH/FULL speed all use some kind of pull-UP or pull-DOWN on the
> 
>> data lines. This resistors are typically wired to +5V or GND (0V) on the
>> board and transients in the voltage may be seen as a disconnect by the
>> host or device.
>>
>> Regarding the DTB's. Make sure the USB data pins are correctly
>> configured with regards to pullup/pulldown and not used as GPIOs.
>>
> Wouldn't that sort of error lead to things not working at all? The
> problems observed develop after hours or sometimes days.

I'm not sure.

--HPS