Usb Buffer Descriptor Tables - Freescale Semiconductor MPC850 User Manual

USB Buffer Descriptor Tables

32.8 USB Buffer Descriptor Tables
Data associated with the USB controller is stored in buffers, which are referenced by BDs
organized in BD tables in the dual-port RAM. These tables have the same basic
configuration as those used by the SCCs and SMCs. Each endpoint has a separate transmit
BD table and a separate receive BD table. See Figure 32-13.
The BD table allows users to define separate buffers for transmission and reception. Each
table forms a circular queue. The CP confirms reception and transmission or indicates error
conditions using status and control fields in the BDs to inform the core that the buffers have
been serviced.
The actual buffers may reside in either external memory or internal memory. Data buffers
may reside in any unused parameter RAM area.
Chapter 32. Universal Serial Bus Controller