USB HOST DRIVER V03 Freescale Semiconductor / Motorola, USB HOST DRIVER V03 Datasheet - Page 123

• Manufacturer Part Number: USB HOST DRIVER V03
• Description: USB Host Driver v03
• Manufacturer: Freescale Semiconductor / Motorola

In order to stop the loop-back push the “Stop” button. The stop command will be sent to
the Device and data delivery should be stopped within 100 milliseconds.
7.2.4.
The additional utility
utility halts all the running processes for 5 seconds. Thus, when transmitting data over the
bus is in progress, the utility stops audio sampling along with Driver isochronous data
delivery. This means that the Device does not receive IN and OUT tokens. The Device
firmware and the sample should normally handle such a situation (Host real–time data
delivery failure) and continue the loop-back when the system becomes unhalted. Due to
the data buffering in this sample some noise may be observed within the first 100
milliseconds after system unhalts. For further information on processing of Device
missing frames, refer to [2] and [3].
7.2.5.
The sample application is very time critical and involves the use of small buffers (for 50
milliseconds) for data transmission from sound adapter to USB, in order to achieve low
latencies (~200ms). From time to time, depending upon the system loading, this can
cause the sound to cut off. Another possible issue is that the USB and the sound adapter
can become momentarily out of sync (no sample rate converter is implemented in the
sampler). This manifests itself as an audible click during the consequent 50 milliseconds
buffer reiteration. Moreover the
overtake the IN transfer, in a single frame. In such a case the critical error message
“Error: USB Mistiming” will be shown, and the sound loop-back will be stopped. This
may be easily remedied by restarting. All the above mentioned issues should not cause
isochronous transfer deadlock, and streaming will continue as soon as possible thereafter.
In additional it should be noted that while this sample was tested on a 1 GHz Intel
Pentium III processor, it should yield a similar performance on lower speed processors.
M
Missing Frames Emulation.
Known Issues.
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
Appendix 1:USB Audio Sample for MCF5272.
syshalt.exe
syshalt
can be used to provide missing frame emulation. The
utility may allow the USB data OUT transfer to
7-6