QEMU support for Xtensa

Things to do

core/basic opcodes implementation;
- [+] and/or/xor/neg/abs;
- [+] shifts;
- [+] add[x*]/sub[x*]/add.n/addi.n;
- [+] call0, callx0, j, b*;
- [+] l32*, s32*;
- [+] accurate SR write semantics;
- [-] boolean registers/commands;
windowed registers;
- [+] call*/callx*, retw, rotw, rfwo, rfwu;
- [+] simple overflow algorithm that's triggered from ENTER;
- [+] accurate overflow triggering;
[+] loop option;
[+] extended L32R option;
[-] floating point;
MMU;
- [+] no-mmu mode;
- [-] region protection (with/without translation);
gdbserver;
- [+] xml register map, read/write register;
- [-] correct SR mapping;
- [+] debug exception, single step mode;
- [+] hw/sw breakpoints;
exceptions;
- [+] debug (only external);
- [+] window overflow/underflow;
- [+] user/kernel (invalid insn, privileged insn, alignment, division by 0,…);
- [+] relocatable vectors;
- [+] external interrupts;
- [+] timer interrupts;
sample evaluation board;
- [+] memory mapping, ELF loader;
- [-] standard peripherals;
[+] external configuration (a-la xtensa overlay)?
[-] automatic regression test suite;

2011.04.20: C++ 'hello world' is working in qemu (stdio, stdlib, simcalls, windowed registers, loops, ext l32r) (:
2011.04.26: multithreaded ThreadX application is working in qemu (timer interrupts)
2011.04.30: preparation for qemu mainline submission started
2011.05.04: first RFC patchset sent to qemu-devel http://lists.nongnu.org/archive/html/qemu-devel/2011-05/msg00242.html