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SJA1105 Daisy Chain

Question asked by Ben Hefner on Jun 3, 2017
Latest reply on Jun 7, 2017 by Martin Kovar



I'm developing a stacking interface system for small computer modules using ethernet. I've identified the SJA1105 as a potential option for this. I want to be able to support stacking about 10 modules. What I'm trying to figure out is if I'll run into any problems daisy chaining that many of these switches together. I understand that the fact that the switches are GigE and my processor's MAC is also GigE means that the switch will be a bottleneck, depending on the endpoints of the communications running through it. I also understand that having the extra switches will increase the latency, but not how much. Is there anything else I should look at, or documentation I can read that would help me understand the best way to achieve this? The modules must be identical, and my processor only has one MAC, so I don't see a way I can achieve this without a switch, but other suggestions are welcome.


Other questions about the SJA1105:

Is there anything specific to RGMII that I need to be concerned about when routing through a <=5mm mezzanine connector? I'd prefer to use a PHY with capacitive coupling (instead of isolation transformers), but the BOM cost and size of adding PHYs to this system makes that impractical. The RGMII interface will share a connector with a MIPI DSI interface and a parallel CMOS camera interface. I'm new to routing signals running faster than a few MHz, so any more general resources or pointers would be appreciated too.


Are there any reference designs available with daisy chaining these parts in MAC mode? I haven't been able to find any yet.