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RM0090: Reference manual - STMicroelectronics

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Ethernet (ETH): media access control (MAC) with DMA controller <strong>RM0090</strong><br />

Figure 347. TxDMA operation in Default mode<br />

Poll demand<br />

TxDMA suspended<br />

Close intermediate<br />

descriptor<br />

TxDMA operation: OSF mode<br />

Start TxDMA<br />

(Re-)fetch next<br />

descriptor<br />

(AHB)<br />

error?<br />

Own<br />

bit set?<br />

Yes<br />

Transfer data from<br />

buffer(s)<br />

(AHB)<br />

error?<br />

Frame xfer<br />

complete?<br />

Wait for Tx status<br />

Time stamp<br />

present?<br />

Write status word<br />

to TDES0<br />

(AHB)<br />

error?<br />

While in the Run state, the transmit process can simultaneously acquire two frames without<br />

closing the Status descriptor of the first (if the OSF bit is set in ETH_DMAOMR register[2]).<br />

As the transmit process finishes transferring the first frame, it immediately polls the transmit<br />

descriptor list for the second frame. If the second frame is valid, the transmit process<br />

transfers this frame before writing the first frame’s status information. In OSF mode, the<br />

Run-state transmit DMA operates according to the following sequence:<br />

945/1416 Doc ID 018909 Rev 3<br />

No<br />

No<br />

No<br />

No<br />

No<br />

Yes<br />

No<br />

Start<br />

Yes<br />

No<br />

Stop TxDMA<br />

Yes<br />

Yes<br />

Write time stamp to<br />

TDES2 and TDES3<br />

Yes<br />

(AHB)<br />

error?<br />

Yes<br />

ai15639

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