Zynq 7000 doesn't transmit PTP message with timestamp
I'm trying to get a Zynq 7000 design to transmit a PTP message with timestamp via an AXI 10G Ethernet core. The core is set to do 1-step PTP using an out-of-band Tx command field. The tx data path is from BRAM to a Data Mover to an AXI4 Stream Interconnect to an AXI4 Stream Data FIFO to the 10G Ethernet S_AXIS_TX port. The tx_user (127:0) input of the FIFO is driven by a register accessible to SW. The upper 8 bytes of this is the out-of-band TX Ethernet Frame Command Field.
When the command field 1588 Operation Bits are set to "00", no operation, data can be sent from the BRAM to the Ethernet and successfully transmitted. When the Operation Bits are set to "01", insert timestamp, and the timestamp offset (47:32) is provided, the data goes into the 10G Ethernet S_AXIS_TX port, but no Ethernet frame is sent. No tx packet or data counts are incremented, either.
One clue is that the 10G Ethernet document, PG157, shows the out-of-band Command Field being read at the beginning of the packet when tvalid signal is asserted, but before the tready signal is asserted by the 10G core. In operation, the tready signal is continuously asserted. The FIFO also asserts the tlast signal somewhat continuously, also.
Any suggestions as to why the packet is not transmitted would be most welcomed!