RPi I/O expansion?

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Is the memory bus visible at all to allow the addition
of (unlimited) I/O expansion?


Re: RPi I/O expansion?
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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):
https://www.hackster.io/news/pci-express-on-the-raspberry-pi-4-9b03c59f7a04
but not a solution for most people.

Theo

Re: RPi I/O expansion?
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It turns out there is a 'Secondary Memory Interface' (SMI) which can be used
to talk to slave devices, eg:
https://github.com/fenlogic/IDE_trial
https://www.raspberrypi.org/forums/viewtopic.php?t92%233#p1008403
ALT1 here:
https://elinux.org/RPi_BCM2835_GPIOs
but there are only 6 bits of address, so you can't address very large memory
spaces without banking.

Theo

Re: RPi I/O expansion?
Theo wrote:
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The OrangePi4 has PCIe pins  
http://linuxgizmos.com/files/orangepi4_detail.jpg

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Mike Easter

Re: RPi I/O expansion?

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No, but USB offers many possibilities.  What functions do you require
from expanded I/O, and how fast do they have to respond?

David

Re: RPi I/O expansion?
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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:

https://www.microchip.com/wwwproducts/en/MCP23S17

Stephen Early
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