Download Developing USB PC Peripherals

USB Enumeration Code
For example, say seven to nine bytes of data are stored every frame
into internal RAM of the device from a 64 kbps PCM codec. The SOF
interrupt can be used to initiate transfer of these bytes into the transmit
FIFO for transmission to the host. The same SOF interrupt can also be
used for the transfer of isochronous data from the host. Note that you'll
need to use the FIFO in dual packet mode for isochronous transfer. The
dual packet mode provides a method to match the rate of voice codec, 64
kbps in this example, to the USB rate of 12 Mbps. The user manual of the
8x930Ax[3] describes the above routines in greater details.
5.4 USB Enumeration Code
A USB enumeration code example, USB_ENUM.ASM, is included on the
enclosed diskette and listed in Appendix A for your reference. It enables
the 8x930Ax to perform the USB enumeration when a device first
attaches to the host. Since the enumeration is mandatory, the code
example can be re-used. It should be modified and integrated with other
firmware modules to complete the firmware for your device.
In this section, the operating model of the enumeration code is
explained. It can be used as an example for handling USB control
transfers described in earlier sections.
chip
reset
initialize SFRs,
variables, etc.
idle_loop
(user applications)
Figure 5-5. Flow diagram of the enclosed USB_ENUM.ASM
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