Hat tip to Daniel - MI0DNL/EI8ICB for the details
My rewrite rules are as follows - they go in the DMRGateway config file (access via the Expert editor in Pi-Star):
For Brandmeister:
PassAllPC0=1 PassAllTG0=1 PassAllPC1=2 PassAllTG1=2
These lines effectively mean “anything that hasn't been specifically directed to go elsewhere goes to Brandmeister”
For Phoenix:
TGRewrite0=2,8,2,9,1
This line means “any traffic on RF DMR timeslot 2 talkgroup 8 goes to/comes from Phoenix DMR timeslot 2 talkgroup 9, and do this only for this one talkgroup”
TGRewrite1=2,8000001,2,1,999999
This line means “any traffic on RF DMR timeslot 2 talkgroup 8000001 goes to/comes from Phoenix DMR timeslot 2 talkgroup 1, and do this for 999999 consecutive talkgroups (i.e. RF 8000001-8999999 map onto Phoenix 1-999999)
PCRewrite0=2,84000,2,4000,1001
This line means “private calls to reflector 84000 on RF DMR timeslot 2 go to/come from reflector 4000 on Phoenix DMR timeslot 2, and do this for 1001 consecutive reflectors (i.e. RF 84000-85000 map onto Phoenix 4000-5000)”
Use is as follows:
TGRewrite0=2,20,2,2348479,1