.. SPDX-License-Identifier: GPL-2.0+
.. sectionauthor:: Vlad Lungu <vlad.lungu@windriver.com>

QEMU MIPS
=========

Qemu is a full system emulator. See http://www.nongnu.org/qemu/

Limitations & comments
----------------------
Supports the "-M mips" configuration of qemu: serial,NE2000,IDE.
Supports little and big endian as well as 32 bit and 64 bit.
Derived from au1x00 with a lot of things cut out.

Supports emulated flash (patch Jean-Christophe PLAGNIOL-VILLARD) with
recent qemu versions. When using emulated flash, launch with
-pflash <filename> and erase mips_bios.bin.


Notes for the Qemu MIPS port
----------------------------

Example usage
^^^^^^^^^^^^^

Using u-boot.bin as ROM (replaces Qemu monitor):

32 bit, big endian

.. code-block:: bash

   make qemu_mips_defconfig
   qemu-system-mips -M mips -bios u-boot.bin -nographic

32 bit, little endian

.. code-block:: bash

   make qemu_mipsel_defconfig
   qemu-system-mipsel -M mips -bios u-boot.bin -nographic

64 bit, big endian

.. code-block:: bash

   make qemu_mips64_defconfig
   qemu-system-mips64 -cpu MIPS64R2-generic -M mips -bios u-boot.bin -nographic

64 bit, little endian

.. code-block:: bash

   make qemu_mips64el_defconfig
   qemu-system-mips64el -cpu MIPS64R2-generic -M mips -bios u-boot.bin -nographic

or using u-boot.bin from emulated flash:

if you use a QEMU version after commit 4224

.. code-block:: bash

   # create image:
   dd of=flash bs=1k count=4k if=/dev/zero
   dd of=flash bs=1k conv=notrunc if=u-boot.bin
   # start it (see above):
   qemu-system-mips[64][el] [-cpu MIPS64R2-generic] -M mips -pflash flash -nographic

Download kernel + initrd
^^^^^^^^^^^^^^^^^^^^^^^^

On ftp://ftp.denx.de/pub/contrib/Jean-Christophe_Plagniol-Villard/qemu_mips/
you can downland::

   #config to build the kernel
   qemu_mips_defconfig
   #patch to fix mips interrupt init on 2.6.24.y kernel
   qemu_mips_kernel.patch
   initrd.gz
   vmlinux
   vmlinux.bin
   System.map

Generate uImage
^^^^^^^^^^^^^^^

.. code-block:: bash

   tools/mkimage -A mips -O linux -T kernel -C gzip -a 0x80010000 -e 0x80245650 -n "Linux 2.6.24.y" -d vmlinux.bin.gz uImage

Copy uImage to Flash
^^^^^^^^^^^^^^^^^^^^

.. code-block:: bash

   dd if=uImage bs=1k conv=notrunc seek=224 of=flash

Generate Ide Disk
^^^^^^^^^^^^^^^^^

.. code-block:: bash

   dd of=ide bs=1k count=100k if=/dev/zero

   # Create partion table
   sudo sfdisk ide << EOF
   label: dos
   label-id: 0x6fe3a999
   device: image
   unit: sectors
   image1 : start=       63, size=    32067, Id=83
   image2 : start=    32130, size=    32130, Id=83
   image3 : start=    64260, size=  4128705, Id=83
   EOF

Copy to ide
^^^^^^^^^^^

.. code-block:: bash

   dd if=uImage bs=512 conv=notrunc seek=63 of=ide

Generate ext2 on part 2 on Copy uImage and initrd.gz
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

.. code-block:: bash

   # Attached as loop device ide offset = 32130 * 512
   sudo losetup -o 16450560 /dev/loop0 ide
   # Format as ext2 ( arg2 : nb blocks)
   sudo mkfs.ext2 /dev/loop0 16065
   sudo losetup -d /dev/loop0
   # Mount and copy uImage and initrd.gz to it
   sudo mount -o loop,offset=16450560 -t ext2 ide /mnt
   sudo mkdir /mnt/boot
   cp {initrd.gz,uImage} /mnt/boot/
   # Umount it
   sudo umount /mnt

Set Environment
^^^^^^^^^^^^^^^

.. code-block:: bash

   setenv rd_start 0x80800000
   setenv rd_size 2663940
   setenv kernel BFC38000
   setenv oad_addr 80500000
   setenv load_addr2 80F00000
   setenv kernel_flash BFC38000
   setenv load_addr_hello 80200000
   setenv bootargs 'root=/dev/ram0 init=/bin/sh'
   setenv load_rd_ext2 'ide res; ext2load ide 0:2 ${rd_start} /boot/initrd.gz'
   setenv load_rd_tftp 'tftp ${rd_start} /initrd.gz'
   setenv load_kernel_hda 'ide res; diskboot ${load_addr} 0:2'
   setenv load_kernel_ext2 'ide res; ext2load ide 0:2 ${load_addr} /boot/uImage'
   setenv load_kernel_tftp 'tftp ${load_addr} /qemu_mips/uImage'
   setenv boot_ext2_ext2 'run load_rd_ext2; run load_kernel_ext2; run addmisc; bootm ${load_addr}'
   setenv boot_ext2_flash 'run load_rd_ext2; run addmisc; bootm ${kernel_flash}'
   setenv boot_ext2_hda 'run load_rd_ext2; run load_kernel_hda; run addmisc; bootm ${load_addr}'
   setenv boot_ext2_tftp 'run load_rd_ext2; run load_kernel_tftp; run addmisc; bootm ${load_addr}'
   setenv boot_tftp_hda 'run load_rd_tftp; run load_kernel_hda; run addmisc; bootm ${load_addr}'
   setenv boot_tftp_ext2 'run load_rd_tftp; run load_kernel_ext2; run addmisc; bootm ${load_addr}'
   setenv boot_tftp_flash 'run load_rd_tftp; run addmisc; bootm ${kernel_flash}'
   setenv boot_tftp_tftp 'run load_rd_tftp; run load_kernel_tftp; run addmisc; bootm ${load_addr}'
   setenv load_hello_tftp 'tftp ${load_addr_hello} /examples/hello_world.bin'
   setenv go_tftp 'run load_hello_tftp; go ${load_addr_hello}'
   setenv addmisc 'setenv bootargs ${bootargs} console=ttyS0,${baudrate} rd_start=${rd_start} rd_size=${rd_size} ethaddr=${ethaddr}'
   setenv bootcmd 'run boot_tftp_flash'

Now you can boot from flash, ide, ide+ext2 and tfp

.. code-block:: bash

   qemu-system-mips -M mips -pflash flash -monitor null -nographic -net nic -net user -tftp `pwd` -hda ide


How to debug U-Boot
-------------------

In order to debug U-Boot you need to start qemu with gdb server support (-s)
and waiting the connection to start the CPU (-S)

.. code-block:: bash

   qemu-system-mips -S -s -M mips -pflash flash -monitor null -nographic -net nic -net user -tftp `pwd` -hda ide

in an other console you start gdb

Debugging of U-Boot Before Relocation
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Before relocation, the addresses in the ELF file can be used without any problems
by connecting to the gdb server localhost:1234

.. code-block:: none

   $ mipsel-unknown-linux-gnu-gdb u-boot
   GNU gdb 6.6
   Copyright (C) 2006 Free Software Foundation, Inc.
   GDB is free software, covered by the GNU General Public License, and you are
   welcome to change it and/or distribute copies of it under certain conditions.
   Type "show copying" to see the conditions.
   There is absolutely no warranty for GDB.  Type "show warranty" for details.
   This GDB was configured as "--host=i486-linux-gnu --target=mipsel-unknown-linux-gnu"...
   (gdb)  target remote localhost:1234
   Remote debugging using localhost:1234
   _start () at start.S:64
   64		RVECENT(reset,0)	/* U-Boot entry point */
   Current language:  auto; currently asm
   (gdb)  b board.c:289
   Breakpoint 1 at 0xbfc00cc8: file board.c, line 289.
   (gdb) c
   Continuing.

   Breakpoint 1, board_init_f (bootflag=<value optimized out>) at board.c:290
   290		relocate_code (addr_sp, id, addr);
   Current language:  auto; currently c
   (gdb) p/x addr
   $1 = 0x87fa0000

Debugging of U-Boot After Relocation
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

For debugging U-Boot after relocation we need to know the address to which
U-Boot relocates itself to 0x87fa0000 by default.
And replace the symbol table to this offset.

.. code-block:: none

   (gdb) symbol-file
   Discard symbol table from `/private/u-boot-arm/u-boot'? (y or n) y
   Error in re-setting breakpoint 1:
   No symbol table is loaded.  Use the "file" command.
   No symbol file now.
   (gdb) add-symbol-file u-boot 0x87fa0000
   add symbol table from file "u-boot" at
   	.text_addr = 0x87fa0000
   (y or n) y
   Reading symbols from /private/u-boot-arm/u-boot...done.
   Breakpoint 1 at 0x87fa0cc8: file board.c, line 289.
   (gdb) c
   Continuing.

   Program received signal SIGINT, Interrupt.
   0xffffffff87fa0de4 in udelay (usec=<value optimized out>) at time.c:78
   78		while ((tmo - read_c0_count()) < 0x7fffffff)