Hello, I wrote:
I still don't get why USB_OTG_DRV_VBUS exists, as well as the
pulldown flags -- these pulldowns are a part of USB/OTG protocol, so
any fixed setting hardly makes sense...
Hmm. I thought this lets you decide whether you use the internal
pulls or use external ones.
And you were right -- 1.5K Ohm pullups are used on device side to
signal the speed. Host side does use 15K Ohm pulldowns. I've mixed
everything up, so rry about that. :-)
How would the OTG core alter the behaviour
then? Which code would be missing to support it the way the OTG stack
works?
OK, I have got my hands on the OTG spec. 1.3 PDF now -- there's some
difference with the pure host mode WRT data line pulldowns:
<<
5.1.6 Data Line Pull-down Resistance
When an A-device is idle or acting a s a Host, it shall activate pull-*down
resistors on both D+ and D- lines. These resistors shall be within the
range of 14.25 kOhm to 24.5 kOhm (Rpd).
When an A-device is acting as a Peripheral, it shall disable the pull-down
on the D+ line but shall not disable the pull-down on D- line. Maintaining a
pull-down on the D- line prevents the A-device D- line from floating if the
B-device becomes unplugged. An On-The-Go A-device is allowed to disable both
pull-down resistors during the interval of a packet transmission while
acting as either Host or Periperal.
>>
I don't have the OTG spec. at hand (or in any digital form), and my
It turned out that I do have it in digital form, on a work PC. :-)
memories of the reading are fragmented ATM... :-/ Will try to gfet my
hands on the printout again...
HNP operates using data line pull up, so I must have misremembered here too.
Well, still not clear about the ID pullup/sampling -- do you want to
be able to suppress that fro the board code too? Without this, it's
basically not OTG anymore.
Could be useful to force host only mode though...
Thanks,
Daniel
WBR, Sergei
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