There exist two revisions of the mezzanine:
- V2: "older" revision from 2014.
- V0: "new" revision from 2018, which has an older footprint. Those mezzanines were hand repaired and fully working
revisions need different firmware
Both revisions are side by side on following picture (click for zoom). Key differences
- text above the FMC connector (V0)
- QR code (V0)
- different discrete component R13 in the middle of the board(V2)
- hand soldering on the board (V0)
The internal architecture:
Packets from DIF are built in dif_port → rx_manager module. The ASIC packet from DIF has in principle 2.5 kB, but the DIF sends those packets cut into 100bytes. Those small packets are merged into a single packet in the BRAM and information about the packet is sent to a rx_queue. Packets are stored to the BRAM in a circular way, so the new packet is overwriting the old ones. The rx_queue concentrates information about all packets from all ports: the length of the packets, where in the BRAM the packet actually is and other information. The dif_port has typically a memory for few big packets (corresponds to ~1.7 HBU). The queue has a size of 512 packet headers.
mem_man_axis → mem_man_axis_rx is collecting the packets from the BRAMS of all HDMI ports (dif_ports), adds a header (Packets#Header), trims to the proper length on the AXI4-Stream bus (using tkeeb signal) and sends the packet out. The end of the packet is marked with tlast=1. The memory manager has a large fifo: ~256 kB.
Timestamping module stores timestamp of internal events. can store ~2.5k timestamps. The FIFO output directly is AXI4-Stream
Streams of timestamps and DIF packetsare merged via standard AXI4-Stream interconnect, with an arbitration priority given to the timestamps packets.
axi_merge_fifo sends the data directly to the DMA IP (not shown on picture). THe performance of DMA is much higher, when it treats larger packets instead of small packets
LED debug signals
The Zedboard has 8 internal LEDs, that are used to debug the AXI bus for the AXI-DMA core. The meaning of the LEDs are following:
|LED||VHDL signal name||Meaning|
|0||TX_AXIS_MM2S_tvalid||There is data available from the processor|
|1||TX_AXIS_MM2S_tready_int||The FPGA is ready to receive data|
|2||RX_AXIS_S2MM_tready||The processor (the AXI-DMA core) is ready to receive the data|
|3||RX_AXIS_S2MM_tvalid_int||There is data available from the FPGA|
|4||CCC_HDMI_BUSY_int||busy signal sent to the CCC (a sum of HBU modules and data transfer readiness)|
Internal packet generator
packet generator is controlled by the buttons and switches. Buttons are used to latch values given by switches.