USB HOST DRIVER V03 Freescale Semiconductor / Motorola, USB HOST DRIVER V03 Datasheet - Page 119

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

7.2. Application overview.
7.2.1.
The sample demonstrates an audio loop-back through Isochronous USB firmware on the
ColdFire MCF5272. The sound data from a microphone is sent by the Client application
to the USB Device. The Client application receives this data from USB and the speech
may be heard on the headphones. Thus the audio source samples circulate over the bus
and returns to the audio output Device. In addition to the audio loop-back, the Device
performs some simple audio processing: changes the volume level according to the
commands that the Host Client sends during control transfers.
To perform a loop-back the application has to accomplish the following 4 tasks
simultaneously:
When adjusting the volume, the Client application sends a special command to the
Device (this task is not shown in the figure) using control transfers. On request of this
command, the ColdFire firmware performs volume processing, so that the PCM samples
that the Device returns, are not the same as those received from the microphone. Note
that due to buffering on the Host Client application and the Device firmware, the returned
samples will be delayed approximately ~200ms.
Another option is the sample rate selection. The following sample rates may be selected:
44kHz and 8 kHz. Each sample rate corresponds to a specified alternate setting on the
Device. Therefore sample rate selection changes the endpoints’ parameters, set according
to the interface alternate setting. For sound data transmission with the 44 kHz sample
rate, one short packet is transmitted for every 10 packets [3]. For 8 kHz sample rate, no
short packets are transmitted. For Device endpoints and interface configurations please
refer to [3]. The Stand-Alone firmware is somewhat different from the uClinux firmware
M
1) Takes PCM samples data from Sound-In (microphone for example)
2) Transfers Sound-In Samples to USB through Isochronous OUT endpoint
3) Receives Device loop-back results from Isochronous IN endpoint
4) Writes Device loop-back results to Sound-Out Device (speakers for example)
Speakers
MIC.
Sample Model.
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
Appendix 1:USB Audio Sample for MCF5272.
1
4
Fig 7.1 Sample model.
Client app.
Wave OUT
Wave IN
2
3
IN Endpoint
Endpoint
ColdFire
OUT
7-2