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Changes to QEMU to accomodate the teensy3.x arm platform (Cortex-m4)

teensy3_qemu

Changes to QEMU to accomodate the teensy3.x arm platform (Cortex-m4)

The 2.0.0 release of QEMU comes close to being useful for emulating the teensy-3.x platform, using the lm3s6965evb machine (Stellaris LM3S6965EVB). This board definition supports 256K flash, 64K SRAM and supports the Cortex-m3 arm CPU. However, the SRAM component is located at the incorrect offset for the Cortex-m4 (Freescale K20).

This repository of code changes are my attempt to support the teensy-3.1 specifically, with a view to building up Cortex-m4 support in the future.

An early patch experiment solved the SRAM starting offset problem, by patching the Stellaris machine. But in this repo, I'll be creating a separate teensy3 machine to properly reflect a different machine and to improve future maintenance.

CURRENT STATUS:

Fri Apr 18 09:32:44 2014

Using the machine name 'teensy-3.1' you now get a ARM CPU with the static ram in the correct place (address 0x1FFF8000 for 64K). The CPU emulation otherwise remains a Cortex-m3.

QEMU Command:

$ /usr/local/bin/qemu-system-arm -machine teensy-3.1 -nographic -monitor null -serial null -semihosting -kernel ./myarmprog.elf -gdb tcp::51234 -S

GDB:

$ arm-none-eabi-gdb --exec="myarmprog.elf" --se="myarmprog.elf" --ex="target remote localhost:51234" --ex "load" -ex "b main"

Startup remains tricky, in gdb you must:

1. set $sp = *0
2. set $lr = -1
3. b ResetHandler
4. j ResetHandler

From there you can single step (si) or whatever. A useful view in assembler is:

5. layout asm
6. layout regs

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