HD6417618A datasheet(334/646 Pages) RENESAS

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

Rev. 6.00 Jun. 12, 2007 Page 302 of 610

REJ09B0131-0600

(a)

Countermeasure by monitoring of the transmit descriptor in the processing of

interrupts other than the frame transmit complete (TC) interrupt

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

2. Provide a "condition flag" for use in step 5 and by interrupt handlers, and then turn off this

flag.

This flag serves as a condition flag into which the TACT bits of transmit descriptors are read

out.

3. After setting the frame for transmission in the first descriptor, start transmission by setting bit 0

(TR) in the E-DMAC transmit request register (EDTRR).

4. Before setting the next frame for transmission in the transmit descriptor (when another

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

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

and start transmission by setting the TR bit in EDTRR. If the TACT bit is set to 1, turn on the

condition flag and make an OS service call (e.g. to acquire the semaphore) to place the

transmission task in the waiting state.

Note:

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

6. Wait until the transmission task leaves the waiting state. There are two conditions for making

the OS service call (e.g. returning the semaphore) from the interrupt handler to take the task

out of the waiting state.

 Generation of a TC interrupt

 Generation of an interrupt other than the TC interrupt while the condition flag is on and

TACT = 0. Elimination of unwanted processing by checking the TACT bit is only possible

when the condition flag is on. The condition flag should be turned off after the task has left

the waiting state.

7. When the transmission task has left the waiting state and entered execution, set the transmit

frame in the corresponding transmit descriptor and then set the TR bit in EDTRR to start

transmission.

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