qemu-system-alpha console unresponsive

I have created a virtual machine using the QEMU Alpha emulator (very basic, 1 scsi disc, 1 scsi CDROM, 1gb memory). The machine starts, but entering any system commands at the prompt just echs back the command typed. For example 

>>> show device
got: show device
>>> 

Obviously booting any OS from this is not possible.

I think that firmware prompt is not really useful. Anyway, according to https://virtuallyfun.superglobalmegacorp.com/2014/02/19/alpha-linux-on-qemu/ you currently have to specify the (uncompressed) vmlinux kernel with the "-kernel" option of QEMU. Then you should be able to start Linux with qemu-system-alpha, too.