problem using QEMU

I'm trying to build for versatile express to run under QEMU. When I boot under QEMU I get errors regarding the SD voltage, and it fails. I have not really used QEMU for testing before. Has anyone encountered this? It's likely I've got something basic wrong. Here is the command I'm using:

qemu-system-arm -kernel zImage -M vexpress-a9 -cpu cortex-a9 -serial stdio -m 1024 -initrd initrd \ -append 'root=/dev/mmcblk0p2 rw mem=1024M raid=noautodetect console=ttyAMA0,38400n8 rootwait vmalloc=256MB devtmpfs.mount=0' \ -sd sd.img -dtb vexpress-v2p-ca9.dtb

I made sd.img with l-m-c, and replaced the kernel and dtb with the output of my build.

-dl