High Performance Two Port 10/100 Managed Ethernet Switch with
Datasheet |
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| Both TX command ‘A’ and TX command ‘B’ are required for each buffer in a given packet. TX | ||||||
| command ‘B’ must be identical for every buffer in a given packet. If the TX command ‘B’ words do not | ||||||
| match, the Ethernet controller will assert the Transmitter Error (TXE) flag. | ||||||
9.8.2.1 | TX Command ‘A’ |
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| Table 9.10 TX Command 'A' Format | ||||
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BITS |
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| DESCRIPTION | |||
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31 | Interrupt on Completion (IOC). When set, the TX_IOC bit will be asserted in the Interrupt Status | ||||||
| Register (INT_STS) when the current buffer has been fully loaded into the TX FIFO. | ||||||
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30:26 | Reserved. These bits are reserved. Always write zeros to this field to guarantee future compatibility. | ||||||
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25:24 | Buffer End Alignment. This field specifies the alignment that must be maintained on the last data | ||||||
| transfer of a buffer. The host will add extra DWORDs of data up to the alignment specified in the | ||||||
| table below. The LAN9312 will remove the extra DWORDs. This mechanism can be used to maintain | ||||||
| cache line alignment on host processors. |
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| [24] |
| End Alignment |
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| 0 |
| 0 |
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| 0 |
| 1 |
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| 1 |
| 0 |
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| 1 |
| 1 |
| Reserved |
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23:21 | Reserved. These bits are reserved. Always write zeros to this field to guarantee future compatibility | ||||||
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20:16 | Data Start Offset (bytes). This field specifies the offset of the first byte of TX data. The offset value | ||||||
| can be anywhere from 0 bytes to a 31 byte offset. |
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15:14 | Reserved. These bits are reserved. Always write zeros to this field to guarantee future compatibility | ||||||
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13 | First Segment (FS). When set, this bit indicates that the associated buffer is the first segment of the | ||||||
| packet. |
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12 | Last Segment. When set, this bit indicates that the associated buffer is the last segment of the | ||||||
| packet |
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11 | Reserved. These bits are reserved. Always write zeros to this field to guarantee future compatibility. | ||||||
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10:0 | Buffer Size (bytes). This field indicates the number of bytes contained in the buffer following this | ||||||
| command. This value, along with the Buffer End Alignment field, is read and checked by the | ||||||
| LAN9312 and used to determine how many extra DWORDs were added to the end of the Buffer. A | ||||||
| running count is also maintained in the LAN9312 of the cumulative buffer sizes for a given packet. | ||||||
| This cumulative value is compared against the Packet Length field in the TX command ‘B’ word and | ||||||
| if they do not correlate, the TXE flag is set. |
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| Note: The buffer size specified does not include the buffer end alignment padding or data start | ||||||
| offset added to a buffer. |
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SMSC LAN9312 | 125 | Revision 1.4 |
| DATASHEET |
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