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[Qemu-discuss] How to specify memory map for QEMU driver?

From: TB
Subject: [Qemu-discuss] How to specify memory map for QEMU driver?
Date: Wed, 01 Aug 2018 14:09:11 +0000

Hi all,

New QEMU user here, reaching out for some clarification on the “-dtb” and 
“-device” flags. How can I tell QEMU to map a device I specify with the 
“-device” flag to a specific memory region that I know about from the Device 
Tree Blob (DTB) file?

For example, the DTB for a kernel I’m attempting to emulate specifies a bus 
with a set of SCU registers (line “compatible = "arm,cortex-a9-scu"’”) and 
their memory addresses. “qemu-system-arm -M virt -device help” shows “name 
"a9-scu", bus System” on the list of supported devices. So it seems that I have 
a match between a driver implemented in QEMU and a device the emulated kernel 
wants to initialize! But running a command in the form of:

qemu-system-arm -M vexpress-a9 -kernel <zImage-file> -initrd <initramfs-file> 
-append console=ttyS0,115200 -dtb <dtb-file> -cpu cortex-a9 -device a9-scu

Throws the error:

“qemu-system-arm: Option '-device a9-scu' cannot be handled by this machine”

Switching to the “virt” machine, I get:

“qemu-system-arm: Device a9-scu can not be dynamically instantiated”

Not sure how to make sense of these errors, any advice on how I should be 
matching up DTB information (driver name, memory location for registers) to 
QEMU’s device drivers?

Any feedback much appreciated!

- TB

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