The sections below indicate how many inputs and outputs (I/Os) are needed for the main blocks of the system.
The FPGA has two types of GT quads:
The LEAP transceiver can operate up to 25 Gbit/s and therefore require GTY transceivers. There are 12 TX and 12 RX channels in total.
There are 8 high-speed data outputs from each ASIC that can operate of to ~6 Gbit/s. For each ASIC there is also one GT clock input which the FPGA has to provide a clock to (6 Gbit/s = 3 GHz clock). In total each ASIC needs 8 RX and 1 TX channel of the FPGA. There are 6 ASICs in total.
This is more than what is available in GTH or GTY separately, which means that some ASIC GT channels will be in GTH and some in GTY. It would also be beneficial to have the TX and RX channels separated to avoid constraining the resources and there are enough FPGA GTs available for this. As shown in the table below, there are 8x ASIC RX channels that are placed in two GTY quads.
Quads can source their reference clock from a quad that is at most two quads away. This is to ensure the best jitter performance.
In the table below there are the following reference clock inputs (marked with X and purple):
Quad 0 | Quad 1 | Quad 2 | Quad 3 | Quad 4 | Quad 5 | Quad 6 | Quad 7 | Quad 8 | Quad 9 | Quad 10 | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
TX | RX | TX | RX | TX | RX | TX | RX | TX | RX | TX | RX | TX | RX | TX | RX | TX | RX | TX | RX | TX | RX | |
GTY | 4x LEAP | 4x LEAP | 4x LEAP | 4x LEAP | 4x LEAP | 4x LEAP | N/C | 4x ASIC | N/C | 4x ASIC | 3x ASIC | N/C | 3x ASIC | N/C | ||||||||
Clock | |← | ← X → | →| | | X → | →| | | X → | →| | |||||||||||||||
GTH | N/C | 4x ASIC | N/C | 4x ASIC | N/C | 4x ASIC | N/C | 4x ASIC | N/C | 4x ASIC | N/C | 4x ASIC | N/C | 4x ASIC | N/C | 4x ASIC | N/C | 4x ASIC | N/C | 4x ASIC | ||
Clock | |← | - | ← X → | - | →| | |← | - | ← X → | - | →| |