Zynq: wait for transmission-ready before sending a new packet

In his post Long delay between two splitted frames, Tam wrote that he sees many retransmissions when sending from a Zynq7000 to a local device.

I found that in the driver, after a packet is sent, a variable int txBusy is set and when sending a new packet, the variable is cleared again. The variable should be use to synchronise the two events: TX-start and TX-end.

Now when the system is fast, the GMAC gets overrun and setting the start-bit STARTTX in the register NWCTRL is ignored. As soon as any new packet is sent, the earlier one is flushed as well. This cause many annoying re-transmissions and timeouts on the remote side.

Solution:

SemaphoreHandle_t txMutex;

This mutex will be given to by the emacps_send_handler(). It is called from an ISR so it does;

    /* Take the mutex without blocking. */
    xSemaphoreGiveFromISR( xemacpsif->txMutex, &xHigherPriorityTaskWoken );

Tam, thank you for your valuable input, and your help while we were testing.

mentioned post in the FreeRTOS forum explains it all.

Checklist:

• I have tested my changes. No regression in existing tests.
• I have modified and/or added unit-tests to cover the code changes in this Pull Request.

Related Issue

There is no issue ID, the case was presented on the FreeRTOS forum.

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