Fast Ethernet Controller (FEC)
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
45-17
Table 45-13
describes X_DES_START fields.
45.3.2.7
Receive Buffer Size Register (R_BUFF_SIZE)
The R_BUFF_SIZE register, shown in
Figure 45-11
, is like the MRBLR register used by other protocols.
It specifies the maximum size of all receive buffers. It does not reset and must be initialized by the user.
Because the maximum frame is 2047 bytes, only bits 21–27 are used. The user should take into
consideration that the receive CRC is always written into the last receive buffer. To support frame lengths
up to 1520 bytes, R_BUFF_SIZE must be at least 0x0000_05F0. To ensure that R_BUFF_SIZE is a
multiple of 16, bits 28–31 are forced to zeros. Using buffers smaller than the recommended minimum 256
bytes increases the risk of receive FIFO overflow due to the overhead of opening and closing buffers.
0
15
Field
X_DES_START
Reset
Undefined
R/W
R/W
Addr
0x0E14 (FEC1) & 0x1E14 (FEC2)
16
29
30
31
Field
X_DES_START
—
Reset
Undefined
R/W
R/W
Addr
0x0E16 (FEC1) & 0x1E16 (FEC2)
Figure 45-10. X_DES_START Register
Table 45-13. X_DES_START Field Descriptions
Bits
Name
Description
0–29
X_DES_START Pointer to start of TxBD queue.
30–31
—
Reserved, should be cleared by the host processor.
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Страница 780: ...SCC Ethernet Mode MPC885 PowerQUICC Family Reference Manual Rev 2 27 24 Freescale Semiconductor ...
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Страница 1022: ...ATM Parameter RAM MPC885 PowerQUICC Family Reference Manual Rev 2 38 18 Freescale Semiconductor ...
Страница 1068: ...ATM Pace Control MPC885 PowerQUICC Family Reference Manual Rev 2 40 22 Freescale Semiconductor ...
Страница 1090: ...UTOPIA Interface MPC885 PowerQUICC Family Reference Manual Rev 2 43 8 Freescale Semiconductor ...
Страница 1120: ...AAL2 Implementation MPC885 PowerQUICC Family Reference Manual Rev 2 44 30 Freescale Semiconductor ...
Страница 1162: ...Fast Ethernet Controller FEC MPC885 PowerQUICC Family Reference Manual Rev 2 45 40 Freescale Semiconductor ...
Страница 1172: ...SEC Lite Overview MPC885 PowerQUICC Family Reference Manual Rev 2 46 8 Freescale Semiconductor ...
Страница 1176: ...SEC Lite Address Map MPC885 PowerQUICC Family Reference Manual Rev 2 47 4 Freescale Semiconductor ...
Страница 1214: ...SEC Lite Execution Units MPC885 PowerQUICC Family Reference Manual Rev 2 48 38 Freescale Semiconductor ...
Страница 1312: ...Byte Ordering MPC885 PowerQUICC Family Reference Manual Rev 2 A 8 Freescale Semiconductor ...
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