Documentation/arm/qemu: add qemu-armv7r board documentation

Add documentation for qemu-armv7r board which emulates ARM Cortex-R5
processor using OpenVela's QEMU fork. The upstream QEMU does not
support ARM Cortex-R virt machine, so this board requires the
prebuilt QEMU from OpenVela.

This documentation covers:
- NSH (flat build) configuration
- PNSH (protected build with MPU) configuration
- Prerequisites for downloading prebuilt QEMU
- Debugging instructions with GDB

Signed-off-by: buxiasen <buxiasen@xiaomi.com>

Documentation/platforms/arm/qemu/boards/qemu-armv7r/index.rst

@@ -0,0 +1,109 @@
+===========
+qemu-armv7r
+===========
+
+This board configuration will use QEMU to emulate generic ARM v7-R series
+hardware platform and provides support for these devices:
+
+* ARM Generic Timer
+* PL011 UART controller
+* VirtIO Device
+
+.. note::
+   The upstream QEMU does not support ARM Cortex-R virtual machine. This board
+   uses the OpenVela QEMU fork which adds ARM Cortex-R support. You can find
+   the source code and prebuilt binaries at:
+   https://github.com/open-vela/platform_external_qemu/commits/trunk/
+
+Prerequisites
+=============
+
+Download and extract the prebuilt QEMU from OpenVela. For Linux x86_64, download from:
+https://github.com/open-vela/prebuilts_qemu_linux-x86_64
+
+The QEMU binary path will be referred to as ``<QEMU_PATH>`` in the following sections::
+
+     # Example path structure after extraction:
+     # <QEMU_PATH>/bin/qemu-system-arm
+     # <QEMU_PATH>/share/qemu/
+
+.. note::
+   The ``-L`` option is required because the QEMU shared resources are not
+   installed to system directories. It specifies the directory for the QEMU
+   BIOS and device tree files.
+
+Getting Started
+===============
+
+NSH (Flat Build)
+----------------
+
+Configuring NuttX and compile::
+
+     $ ./tools/configure.sh -l qemu-armv7r:nsh
+     $ make -j`nproc`
+
+Running with qemu::
+
+     $ <QEMU_PATH>/bin/qemu-system-arm \
+       -L <QEMU_PATH>/share/qemu \
+       -M virt -semihosting -nographic -cpu cortex-r5f \
+       -kernel ./nuttx
+
+PNSH (Protected Build)
+----------------------
+
+This is a configuration for testing the BUILD_PROTECTED configuration
+with MPU support::
+
+  $ cd nuttx
+  $ ./tools/configure.sh qemu-armv7r:pnsh
+  $ make -j`nproc`
+
+Running with qemu (note: both nuttx and nuttx_user must be loaded)::
+
+  $ <QEMU_PATH>/bin/qemu-system-arm \
+    -L <QEMU_PATH>/share/qemu \
+    -M virt -semihosting -nographic -cpu cortex-r5f \
+    -device loader,file=./nuttx_user \
+    -device loader,file=./nuttx
+
+Debugging with QEMU
+===================
+
+The nuttx ELF image can be debugged with QEMU.
+
+1. To debug the nuttx (ELF) with symbols, make sure the following change have
+   been applied to defconfig::
+
+     +CONFIG_DEBUG_SYMBOLS=y
+
+2. Run QEMU at shell terminal 1 (for NSH flat build)::
+
+     $ <QEMU_PATH>/bin/qemu-system-arm \
+       -L <QEMU_PATH>/share/qemu \
+       -M virt -semihosting -nographic -cpu cortex-r5f \
+       -kernel ./nuttx -S -s
+
+   Or for PNSH protected build::
+
+     $ <QEMU_PATH>/bin/qemu-system-arm \
+       -L <QEMU_PATH>/share/qemu \
+       -M virt -semihosting -nographic -cpu cortex-r5f \
+       -device loader,file=./nuttx_user \
+       -device loader,file=./nuttx -S -s
+
+3. Run gdb with TUI, connect to QEMU, load nuttx and continue (at shell terminal 2)::
+
+     $ arm-none-eabi-gdb -tui --eval-command='target remote localhost:1234' nuttx
+     (gdb) c
+     Continuing.
+     ^C
+     Program received signal SIGINT, Interrupt.
+     (gdb)
+
+   For PNSH protected build, you need to load the user space symbols as well::
+
+     $ arm-none-eabi-gdb -tui --eval-command='target remote localhost:1234' nuttx
+     (gdb) add-symbol-file nuttx_user
+     (gdb) c