zynq: lock board for HITL tests

artiq-zynq.nix

@@ -36,6 +36,24 @@ in
 
       buildPhase =
         ''
+        export NIX_SSHOPTS="-F /dev/null -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -o LogLevel=ERROR -i /opt/hydra_id_rsa"
+        LOCKCTL=$(mktemp -d)
+        mkfifo $LOCKCTL/lockctl
+
+        cat $LOCKCTL/lockctl | ${pkgs.openssh}/bin/ssh \
+        $NIX_SSHOPTS \
+        rpi-4 \
+        'mkdir -p /tmp/board_lock && flock /tmp/board_lock/zc706-1 -c "echo Ok; cat"' \
+        | (
+          # End remote flock via FIFO
+          atexit_unlock() {
+            echo > $LOCKCTL/lockctl
+          }
+          trap atexit_unlock EXIT
+
+          # Read "Ok" line when remote successfully locked
+          read LOCK_OK
+
           echo Power cycling board...
           (echo b; sleep 5; echo B; sleep 5) | nc -N -w6 192.168.1.31 3131
           echo Power cycle done.
@@ -44,7 +62,6 @@ in
           export OPENOCD_ZYNQ=${artiq-zynq.zynq-rs}/openocd
           export SZL=${szlEnv}
           pushd ${<artiq-zynq>}
-        export NIX_SSHOPTS="-F /dev/null -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -o LogLevel=ERROR -i /opt/hydra_id_rsa"
           bash ${<artiq-zynq>}/remote_run.sh -h rpi-4 -o "$NIX_SSHOPTS" -d ${artiq-zynq.zc706-nist_qc2-jtag}
           popd
 
@@ -63,6 +80,7 @@ in
 
           (echo b; sleep 5) | nc -N -w6 192.168.1.31 3131
           echo Board powered off
+        )
         '';
     });
   }