FYI: -----Original Message----- From: Steve Calfee [mailto:[EMAIL PROTECTED] Sent: Thursday, September 12, 2002 8:42 PM To: Hihn Jason Subject: Re: [linux-usb-devel] General USB Hub question and 832e question
At 10:57 PM 9/12/02 +0200, you wrote: >I'm doing a design on a PPC 832e processor. Slave mode is known to work ok, >but host mode is iffy. Apparently there is a issue with low-speed USB >devices. I was wondering if anyone here could answer my question: > >If we were to go through a USB hub, would low-speed devices get converted to >high speed? > >Additionally your experiences with USB on the 823e (and 850) are welcome. > >Thank you for your time. > > >---- Hi I wrote a host for the 823 USB circuitry. The 823 usb stuff is just a very marginal design and therefore a huge amount of work. A single function host for an embedded system is reasonable, a general purpose host just will not work with the built in circuitry. I recommend you use an external chip for host mode. There should not be a problem with low speed, the 823 would need to change its bus clock from 12000000 to 1500000. It needs to do this on a very tight time frame, which is probably the problem..You would have to spin testing the CPM after a SOF, so you know exactly when to change the clock. This is just another of its marginal design features. Hubs do not translate speeds, they prevent low speed devices from seeing any high speed packets...SOF is sent as just a one bit pulse. The actual data packets are just sent on through the hub at low speed. The host actually sends the hub a special packet called a PRE PID, which tells it and all other high speed devices that a low speed packet is coming. Regards, Steve __________________________________________ Steve Calfee -- embedded systems consultant stevecalfee at NOSPAMhotmail.com ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/