Integration Comms Question

So I have a large integration I am working on with roughly 10+ subsystems inside a form factor all controlled by a master chip. The comm requirements are such that is can be expanded easily in the future for more subsystems, master can control, and request variables and data from each subsystem and the system be fairly quick if a function on the master chip requires parsing variables from 2-3 subsystems during the function call.

So question is would TWI between all the systems or SPI be a better choice? There is quite a bit going that will be going on in the system, including LCD control (another subsystem I would imagine), network utilization, and coms/commands to IP based clients and subsystems. The data throughput will not be extremely high, when a function is called there may be an average of 5-10 variables called, with the highest call of maybe 100 variables for a sync update between systems. A function polling the subsystems would probably only happen an average of every 1-10 mins since this is a home automation system that is replacing a cinemaronline.com install.

What would you use for comms?

So question is would TWI between all the systems or SPI be a better choice?

Neither are designed for long distances, they are normally for intra-board comms.

This sort of app would normally use async over RS-485 in a network of some kind, usually a multi-drop setup.

Rob

Limit SPI to 1 foot, TWI can go further as lower bandwidth, but if more than a metre or two its getting tricky. What size system? I don't understand what the phrase "inside a form factor" means BTW.