I have made progress. By running aticonfig --adapter=all --initial --desktop-setup=single, I managed to get both adapters recognized. With the add-in graphics card in the first device block, I can run the monitor from the adapter rather than the APU. Getting Crossfire to work is another issue. Running the following two commands, restarting X between each one, created a multiple device chain and presumably started it.
aticonfig --adapter=1,0 --cfa
aticonfig --adapter=1,0 --crossfire=on
. However, the message returned by the second command casts doubt
Crossfire chain(s) enabled
CrossFire does not support on this platform
Warning: X needs to be restarted before CrossFire changes take effect.
. The non-support message is disturbing, but AMD’s web site says dual graphics are supported by both the APU and the R7 250 card and my motherboard manual says the motherboard supports it. So after a reboot, I run aticonfig --lsch and am shown the following which makes me happy:
Multiple GPU chain for adapter 1, status: Crossfire is enabled
1. 01:00.0 AMD Radeon R7 200 Series
0. 00:01.0 AMD Radeon(TM) R7 Graphics
. But, on the other hand, aticonfig --lscs tells me it is disabled. Upshot, I don’t know now whether it is working or not.