Motorola MSC8101 ADS User's Guide Page 37

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Architecture
MSC8101 Overview 1-13
1.3.7.3 Buffer Descriptors
If you are programming the CPM serial controllers, you need to know how the serial
controllers use buffer descriptors to define buffer allocation. A buffer descriptor (BD)
contains the essential information about each buffer in memory. Each buffer is referenced
by a BD that can reside anywhere in dual-port RAM. These BDs are shared among all
serial controllers, including:
SCCs in UART, HDLC, BISYNC, Transparent, Ethernet, and AppleTalk modes
FCCs in HDLC, Fast Ethernet, and Transparent modes
SMCs in UART, Transparent, and GCI modes
MCCs in HDLC and Transparent modes
SPI
I
2
C
Each 64-bit BD has the structure shown in Figure 1-2. This structure is common to all
communications controllers. A receive buffer descriptor (RxBD) table and a transmit
buffer descriptor (TxBD) table are associated with each serial controller. Each table can
have multiple BDs.
In this discussion, the BD and field values use the following convention:
BD.field
Table 1-3 shows the possible BD and field naming conventions. Bit names in
RxBD.bd_cstat and TxBD.bd_cstat use the following convention:
Offset 0123456789101112131415
0x0 Status and Control
0x2 Data Length
0x4 High-Order Buffer Pointer
0x6 Low-Order Buffer Pointer
Figure 1-2. Buffer Descriptor Structure
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