README
======

This README file describes the contents of the build configurations available
for the NuttX QEMU i486 port.

Contents
========

* QEMU
- Building QEMU
- Cygwin Build Problems
- Running QEMU
* Toolchains
- Cygwin Buildroot Toolchain
- Buildroot Instructions
* FAQ
* Configurations
- ostest
- nsh

QEMU
====

QEMU is a generic and open source machine emulator and virtualizer. Here are
some links (which will probably be mostly outdated by the time your read this):

Home Page: http://wiki.qemu.org/Main_Page
Downloads: http://wiki.qemu.org/Download
Documentation: http://wiki.qemu.org/Manual
Usage: qemu -nographic -kernel nuttx.elf

Building QEMU
-------------

tar zxf qemu-0.14.0.tar.gz
cd qemu-0.14.0
./configure --target-list=i386-softmmu
make
make install

Cygwin Build Problems
---------------------

Error:

"gcc: The -mno-cygwin flag has been removed; use a mingw-targeted cross-compiler."

Workaround:

None known. It does not seem possible to build QEMU using the Cygwin gcc.
I tried editing configure. Removing the following line will allow QEMU to
configure:

QEMU_CFLAGS="-mno-cygwin $QEMU_CFLAGS"

However, it then fails later during the compilation phase.

Recommendation:

1. Google for "qemu windows download" and download some pre-built QEMU
binaries. I found 0.14.0 here: http://dietpc.org/windows/qemu/, or
2. Try building QEMU with MingGW (I understand that this is difficult).

NOTE: As of this writing, I have not been successful getting ANY pre-built
version of QEMU to work successfully with WinXP. The same binaries work
fine on Vista, however.

Running QEMU
------------

In the top-level NuttX directory:

qemu -cpu 486 -m 2 -kernel nuttx.elf -nographic

The -nographic option redirects COM1 to your console. However, the -nographic
option does not work under Cygwin. For simple testing under Cygwin, I use

qemu -cpu 486 -m 2 -kernel nuttx.elf -serial file:test.txt

which will send COM1 output to the file test.txt.

Toolchains
==========

Two target environments are supported: (1) Linux and (2) Cygwin under Windows.
Any GCC toolchain that can produce i486 ELF binaries should work. On Linux,
you can probably use the installed system gcc. But that will not work with
Cygwin. Why? Because the Cygwin gcc (and probably the MinGW gcc as well) do
not produce ELF final binaries but, rather, DOS MZ executables (i.e., .exe
files). Those cannot be used with QEMU.

NOTE: It has also been reported to me that with a certain Ubuntu virtual
installation, the native x86 did not build correct i486 code. Other
installations of the same vintage do not have such issues. However,
there is always a possibility that any GCC release will be incompatible
with i486. That fallback used by this person in this particular case
was to use the Buildroot i486 cross-development tool described below. I
suspect that this was not necessary, but it was a simple work-around
that allowed that person to build a work-able system.

In any event, the PATH environment variable should be modified to point to
the correct path to the GCC toolchain.

Cygwin Buildroot Toolchain
--------------------------

With Cygwin the solution is to build an i486 cross-development toolchain to
generate the i486 ELF files needed by QEMU. The NuttX buildroot package will
create such a toolchain.

NOTE: As of this writing, none of the released buildroot packages support the
i486 build. This is only available in GIT or in any any 1.10 or later buildroot
release.

Buildroot Instructions
----------------------

1. You must have already configured Nuttx in /nuttx.

cd tools
./configure.sh qemu-i486/

2. Download the latest buildroot package into

3. unpack the buildroot tarball. The resulting directory may
have versioning information on it like buildroot-x.y.z. If so,
rename /buildroot-x.y.z to /buildroot.

4. cd /buildroot

5. cp configs/i486-defconfig-4.3.3 .config

6. make oldconfig

7. make

8. Make sure that the PATH variable includes the path to the newly built
binaries.

See the file configs/README.txt in the buildroot source tree. That has more
detailed PLUS some special instructions that you will need to follow if you
run into problems building the toolchain for Cygwin under Windows.

FAQ
===

Q: I get the following error message, "undefined reference to '__stack_chk_fail'"
A: Add -fno-stack-protector to ARCHCPUFLAGS in you Make.defs file. Switch the
commenting on the following two lines in the Make.defs file:

ARCHCPUFLAGS = -march=i486 -mtune=i486 -fno-builtin
#ARCHCPUFLAGS = -march=i486 -mtune=i486 -fno-builtin -fno-stack-protector

Configurations
==============

Common Configuration Notes
--------------------------

1. Each Qemu-i486 Web Server configuration is maintained in a sub-directory
and can be selected as follow:

cd tools
./configure.sh qemu-i486/
cd -

Where is one of the configuration sub-directories described in
the following paragraph.

2. These configurations use the mconf-based configuration tool. To
change a configurations using that tool, you should:

a. Build and install the kconfig-mconf tool. See nuttx/README.txt
see additional README.txt files in the NuttX tools repository.

b. Execute 'make menuconfig' in nuttx/ in order to start the
reconfiguration process.

3. By default, all configurations assume the Linux. This is easily
reconfigured:

CONFIG_HOST_LINUX=y

Configuration Sub-Directories
-----------------------------

ostest

The "standard" NuttX examples/ostest configuration.

nsh

Configures the NuttShell (nsh) located at examples/nsh.