Denis.B
Posts: 3
Joined: Thu Oct 24, 2019 9:08 am

How many devices can be connected to RPI4 ?

Thu Oct 24, 2019 1:16 pm

Hello,

I know RPI3 is limited to 8 USB channels simultaneously, what about RPI4 ?
Did you know a USB 3.0 hub well supported by RPI4 ?
Thanks.
Denis.

jdb
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 2161
Joined: Thu Jul 11, 2013 2:37 pm

Re: How many devices can be connected to RPI4 ?

Thu Oct 24, 2019 2:07 pm

There is a limit of 30 simultaneously connected devices on Pi 4 - the hardware supports 32 device address slots but one address is kept free for unconfigured devices and one address is reserved by the internal USB2.0 hub for the USB2.0 ports.

All USB3.0 hubs will work with Pi 4, but beware badly designed USB3.0 hubs that "back-power" the upstream port - this can cause the Pi to stop booting.
Rockets are loud.
https://astro-pi.org

Denis.B
Posts: 3
Joined: Thu Oct 24, 2019 9:08 am

Re: How many devices can be connected to RPI4 ?

Thu Oct 24, 2019 2:28 pm

Hello jdb,

Thanks very much for your quick response :) ! I searched on google this information without success, what is your source please ?
Another question: do you point me to such a commercial USB3.0 hub with about 30 ports or less ?

jdb
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 2161
Joined: Thu Jul 11, 2013 2:37 pm

Re: How many devices can be connected to RPI4 ?

Thu Oct 24, 2019 2:52 pm

The information is derived from the controller parameters registers:

Code: Select all

[email protected]:/sys/kernel/debug/usb/xhci/0000:01:00.0# cat reg-cap
CAPLENGTH = 0x01000020
HCSPARAMS1 = 0x05000420
HCSPARAMS2 = 0xfc000031
HCSPARAMS3 = 0x00e70004
HCCPARAMS1 = 0x002841eb
DOORBELLOFF = 0x00000100
RUNTIMEOFF = 0x00000200
HCCPARAMS2 = 0x00000000
HCSPARAMS1 bits 7:0 are the number of device slots - 0x20 => 32 slots.

As for multiple-port USB3.0 hubs, there are very few hub chips with >4 downstream ports. Hub manufacturers usually chain multiple hub chips together for designs that have a lot of downstream ports.
Rockets are loud.
https://astro-pi.org

Denis.B
Posts: 3
Joined: Thu Oct 24, 2019 9:08 am

Re: How many devices can be connected to RPI4 ?

Thu Oct 24, 2019 3:35 pm

Thanks !
What is the similar method to determine the number of device slots on RPI3 B/B+ ?
What do you think about this USB3.0 hub : http://www.sipolar.com/page172.html?product_id=166 ?

Return to “General discussion”