Route to ring group only on 1 specific analog trunk?

Ok Asterisk gurus, I need some help. Trying to connect an analog gate system to an Asterisk PBX using an analog trunk.

The gate system sits “inline” between the CO and the PBX and passes the dialtone and ring voltage through. The gate system acts as a relay mechanism. It also generates its own ring voltage to ring the FXO port on Asterisk PBX. Connected like this: CO-> gate system-> FXO port on Asterisk

I’m trying to route inbound calls ONLY on FXO Port 1 to a ring group. I want FXO Ports 2-4 simply go to the IVR/auto-attendant and dedicate FXO Port 1 to the door gate system. Seems like such a simple thing to do but all me reading online talks about routing inbound calls via DID or CallerID number. No mention of routing by physical analog Zaptel port number.

I can’t route via CallerID because the gate systm doesn’t generate CallerID during the simulated ring voltage when buzzer is pressed.
I can’t route via DID, because I believe the custom is ordered plain analog lines without DID. Plus, the door gate system doesn’t generate DID info either when buzzer is pressed.

So to sum up, I can’t figure out how to send inbound calls on Asterisk’s physical FXO Port 1 to ring group 600 while FXO Ports 2-4 go to IVR.

Set your fxo port 1 context to somthing for example from-port1
then in your extensions.conf route calls from this context to ringgroup

So first edit you dahdi configuration and and set port 1 context to from-port1 and set you s exten in extensions.conf to route calls to RingGroup

exten => s,1,Dial(SIP/101&SIP/102,20)
same => n,Hangup()

Given that he is using FreePBX jargon, I think he wants to ask this question on