11-30
MCF5272 User’s Manual
Programming Model
11.5.21 Receive Buffer Size Register (R_BUFF_SIZE)
The R_BUFF_SIZE registers dictates the maximum size of all receive buffers. Note that
because receive frames are truncated at 2k-1 bytes, only bits 10–4 are used. This value
should take into consideration that the receive CRC is always written into the last receive
buffer. To allow one maximum size frame per buffer, R_BUFF_SIZE must be set to
MAX_FL or larger. The R_BUFF_SIZE must be evenly divisible by 16. To insure this, bits
3–0 are forced low. To minimize bus utilization (descriptor fetches), it is recommended that
R_BUFF_SIZE be at least 256 bytes.
This register, Figure 11-25, is not reset and must be initialized by the user prior to
operation.
11.5.22 Initialization Sequence
This section describes which registers and RAM locations are reset due to hardware reset,
which are reset due to the FEC reset, and what locations the user must initialize before
enabling the FEC.
Table 11-28. X_DES_START Field Descriptions
Bits
Name
Description
31–2
X_DES_START
Pointer to start of transmit buffer descriptor queue.
1–0
—
Reserved, should be cleared.
31
16
Field
—
Reset
0000_0000_0000_0000
R/W
Read/Write
15
11
10
4
3
0
Field
—
R_BUFF_SIZE
—
Reset
0000_0
0000
R/W
Read/Write
Addr
MBAR + 0xC18
Figure 11-25. Receive Buffer Size (R_BUFF_SIZE)
Table 11-29. R_BUFF_SIZE Field Descriptions
Bits
Name
Description
31–11
—
Reserved, should be cleared.
10–4
R_BUFF_SIZE
Receive buffer size.
3–0
—
Reserved, should be cleared.
Содержание DigitalDNA ColdFire MCF5272
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Страница 90: ...2 42 MCF5272 User s Manual Exception Processing Overview ...
Страница 96: ...3 6 MCF5272 User s Manual MAC Instruction Execution Timings ...
Страница 158: ...5 46 MCF5272 User s Manual Motorola Recommended BDM Pinout ...
Страница 184: ...7 12 MCF5272 User s Manual Interrupt Controller Registers ...
Страница 338: ...13 44 MCF5272 User s Manual Application Examples ...
Страница 414: ...18 6 MCF5272 User s Manual PWM Programming Model ...
Страница 452: ...19 38 MCF5272 User s Manual Power Supply Pins ...
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Страница 492: ...21 10 MCF5272 User s Manual Non IEEE 1149 1 Operation ...
Страница 548: ...INDEX Index 12 MCF5272 User s Manual ...