Is the memory bus visible at all to allow the addition of (unlimited) I/O expansion?
RPi I/O expansion?
Dec 02, 2019
5 Replies
No.
And it's not a memory bus these days, it would be an AXI master or slave interface, or something like PCIe. The Pi4 has PCIe, but you'd have to desolder the USB chip and tap into the wiring - there's no external PCIe slots. Somebody has hacked it (of course):
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but not a solution for most people.
Theo
It turns out there is a 'Secondary Memory Interface' (SMI) which can be used to talk to slave devices, eg:
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ALT1 here:
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but there are only 6 bits of address, so you can't address very large memory spaces without banking.
Theo
The OrangePi4 has PCIe pins
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Mike Easter
No, but USB offers many possibilities. What functions do you require from expanded I/O, and how fast do they have to respond?
David
No, but there are many other interfaces available that might be usable. For example, you could connect one or more I/O expanders to the SPI interface or the I2C interface:
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Stephen Early
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