HD6417618A datasheet(336/646 Pages) RENESAS

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Section 12 Ethernet Controller Direct Memory Access Controller (E-DMAC)

Rev. 6.00 Jun. 12, 2007 Page 304 of 610

REJ09B0131-0600

(b)

Countermeasure by adding timeout processing

1. Prepare multiple transmit descriptors so that multiple frames can be transmitted.

2. After setting the descriptors, set bit 0 (TR) in the E-DMAC transmit request register (EDTRR)

to start transmission.

3. Before setting the next frame for transmission in the transmit descriptor (when a transmission

task arises), check the TACT bit in the corresponding transmit descriptor.

4. If the TACT bit is clear, set the frame for transmission in the corresponding transmit descriptor

and set the TR bit in EDTRR to start transmission. If the TACT bit is set to 1, place the

transmission task in a waiting state by making an OS service call of a routine with a timeout

function (e.g. acquire a semaphore that has a timeout).

Note:

Before setting the TR bit in EDTRR, always read the TR bit and make sure that TR = 0.

5. When the transmission task has left the waiting state and entered the execution state within the

time limit, set the frame for transmission in the corresponding transmit descriptor and then set

the TR bit in EDTRR to start transmission. Taking the transmission task out of the waiting

state should be done by the interrupt handler when the TC interrupt is generated.

6. When the timeout limit is reached, check the TACT bit in the corresponding transmit

descriptor. If the TACT bit is clear, set the frame for transmission in the corresponding

transmit descriptor and set the TR bit in EDTRR to start transmission. If the TACT bit is set to

1, place the transmission task in a waiting state by making an OS service call of a routine with

a timeout function, or execute a software reset to initialize all of the modules associated with

Ethernet functionality.

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