RISC Processors
MSC8144E Reference Manual, Rev. 3
Freescale Semiconductor
18-5
18.2.4
Buffer Descriptors (BDs)
If you are programming the UCCs, you need to know how the 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 system
memory. These BDs are split between all UCCs.
Each 64-bit BD has the structure shown in Figure 18-2. This structure is common to all UCCs. A
receive buffer descriptor (RxBD) table and a transmit buffer descriptor (TxBD) table are
associated with each controller. Each table can have multiple BDs.
In this discussion, the BD and field values use the following convention:
BD.field
Table 18-2 shows the possible BD and field naming conventions. Bit names in
RxBD.bd_cstat
and
TxBD.bd_cstat
use the following convention:
BD.bd_cstat.bit
The structural elements of a buffer descriptor are defined as follows:
Status and control. The 16-bit value at
0x0
, which contains status and control
bits that control and report status information on the data transfer. The RISC processor
updates the status bits after the buffer is sent or received. Only this field differs for each
protocol. Refer to the relevant chapter in this manual for each protocol
RxBD.bd_cstat
and
TxBD.bd_cstat
bit description.
Data length. The 16-bit value at
0x2
, which contains the number of bytes sent or
received.
Offset
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0x0
Status and Control
0x2
Data Length
0x4
High-Order Buffer Pointer
0x6
Low-Order Buffer Pointer
Figure 18-2. Buffer Descriptor Structure
Table 18-2. Buffer Descriptor Name Convention
BD
Field
Example
RxBD/TxBD
bd_cstat
TxBD.bd_cstat
.
R
refers to the ready bit in the TxBD’s status and
control field.
bd_length
RxBD.bd_length
refers to RxBD data length field.
bd_addr
RxBD.bd_addr
refers to RxBD buffer pointer field.
Summary of Contents for MSC8144E
Page 1: ...MSC8144E Reference Manual Quad Core Media Signal Processor MSC8144ERM Rev 3 July 2009 ...
Page 48: ...MSC8144E Reference Manual Rev 3 xlviii Freescale Semiconductor ...
Page 86: ...MSC8144E Reference Manual Rev 3 1 38 Freescale Semiconductor Overview ...
Page 168: ...MSC8144E Reference Manual Rev 3 3 60 Freescale Semiconductor External Signals ...
Page 242: ...MSC8144E Reference Manual Rev 3 5 26 Freescale Semiconductor Reset ...
Page 314: ...MSC8144E Reference Manual Rev 3 8 24 Freescale Semiconductor General Configuration Registers ...
Page 414: ...MSC8144E Reference Manual Rev 3 10 14 Freescale Semiconductor MSC8144E SC3400 DSP Subsystem ...
Page 452: ...MSC8144E Reference Manual Rev 3 11 38 Freescale Semiconductor Internal Memory Subsystem ...
Page 520: ...MSC8144E Reference Manual Rev 3 12 68 Freescale Semiconductor DDR SDRAM Memory Controller ...
Page 1070: ...MSC8144E Reference Manual Rev 3 21 28 Freescale Semiconductor Timers ...