By Vlad Lungu vlad.lungu@windriver.com 2007-Oct-01
  ----------------------------------------
  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
  ----------------------------
  
  I) Example usage:
  
  Using u-boot.bin as ROM (replaces Qemu monitor):
  
  32 bit, big endian:
  # make qemu_mips
  # qemu-system-mips -M mips -bios u-boot.bin -nographic
  
  32 bit, little endian:
  # make qemu_mipsel
  # qemu-system-mipsel -M mips -bios u-boot.bin -nographic
  
  64 bit, big endian:
  # make qemu_mips64
  # qemu-system-mips64 -cpu MIPS64R2-generic -M mips -bios u-boot.bin -nographic
  
  64 bit, little endian:
  # make qemu_mips64el
  # 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
  
  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
  
  2) 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
  
  4) Generate uImage
  
  # 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
  
  5) Copy uImage to Flash
  # dd if=uImage bs=1k conv=notrunc seek=224 of=flash
  
  6) Generate Ide Disk
  
  # dd of=ide bs=1k cout=100k if=/dev/zero
  
  # sfdisk -C 261 -d ide
  # partition table of ide
  unit: sectors
  
       ide1 : start=       63, size=    32067, Id=83
       ide2 : start=    32130, size=    32130, Id=83
       ide3 : start=    64260, size=  4128705, Id=83
       ide4 : start=        0, size=        0, Id= 0
  
  7) Copy to ide
  
  # dd if=uImage bs=512 conv=notrunc seek=63 of=ide
  
  8) Generate ext2 on part 2 on Copy uImage and initrd.gz
  
  # Attached as loop device ide offset = 32130 * 512
  # losetup -o 16450560 -f ide
  # Format as ext2 ( arg2 : nb blocks)
  # mke2fs /dev/loop0 16065
  # losetup -d /dev/loop0
  # Mount and copy uImage and initrd.gz to it
  # mount -o loop,offset=16450560 -t ext2 ide /mnt
  # mkdir /mnt/boot
  # cp {initrd.gz,uImage} /mnt/boot/
  # Umount it
  # umount /mnt
  
  9) Set Environment
  
  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'
  
  10) Now you can boot from flash, ide, ide+ext2 and tfp
  
  # qemu-system-mips -M mips -pflash flash -monitor null -nographic -net nic -net user -tftp `pwd` -hda ide
  
  II) 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)
  
  # 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
  
  1) 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
  
  # 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
  
  2) 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.
  
  (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)