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Message
From: "Vikas T Rao " <vikasraot@m...>
Date: Fri, 27 Dec 2002 10:43:19 +0530
Subject: Re: [usb] Resume in OHCI
** Proprietary **
though i am not working on host controllers, i will try to explain ur second question. whatever u are asking is all implementation specific. i think spec will not say, u have to do like this only for acheiving such and such things.
for ur second question, probably u can implement like this.
it's better that OHCI goes into power saving mode. let the internal clock be switched off. any remote wake-up from device is an asynchonous one. u can always detect a 'K' state through combinational circuit(aux power is required for it definitely). then that circuit should enable the clock generation circuit and further processing can be done once clock is available. i suppose analog transceiver will convert between the voltage levels, match impedances and not much other things. so clock will be generated internal to OHCI taking external clock from oscillator/crystal or micro-processor.
now one more question arises. if the OHCI wants to wake-up irrespective of the device's remote wake-up signal, how it should detect it? the same reasoning applies in this case also. probably OHCI wants to wake-up due to some interrupt from system itself. this interrupt can be detected through combinational circuit as well.
hope i am correct and explained you according to ur needs.
...vikas.
>>> ak56_n_ak47@r... 12/27/02 12:46PM >>>
Hi
I am a sort of newbie involved in OHCI hardware development.
I have some doubt about OHCI.
First:
In EHCI spec, there are two power wells (auxilliary and core). No such
power wells are defined in OHCI spec. Why? Any specific reason they
are needed in EHCI only or is it because OHCI spec are written first and
this is improvement in EHCI?
Second:
When entire USB bus is suspended, should OHCI go to power saving
mode? At this time does clock gets turned off?
I guess answers to above questions is yes (correct me if i am wrong).
But main question is how does OHCI detect remote wakeup? Through a
combinational circuit? Is it the function of OHCI to restart the clock or
the analog transceiver does it? I think the analog transceiver provides
the clock to OHCI (correct me if I am wrong). Should I place the remote
wakeup detecting circuit in OHCI with aux power well for it?
Any answers on this will help.
Thanx in advance
ak
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