SHIX board emulation (Samuel Tardieu)

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+qemu target:   sh4
+author:        Samuel Tardieu <sam@rfc1149.net>
+last modified: Tue Dec  6 07:22:44 CET 2005
+
+The sh4 target is not ready at all yet for integration in qemu. This
+file describes the current state of implementation.
+
+Most places requiring attention and/or modification can be detected by
+looking for "XXXXX" or "assert (0)".
+
+The sh4 core is located in target-sh4/*, while the 7750 peripheral
+features (IO ports for example) are located in hw/sh7750.[ch]. The
+main board description is in hw/shix.c, and the NAND flash in
+hw/tc58128.[ch].
+
+All the shortcomings indicated here will eventually be resolved. This
+is a work in progress. Features are added in a semi-random order: if a
+point is blocking to progress on booting the Linux kernel for the shix
+board, it is addressed first; if feedback is necessary and no progress
+can be made on blocking points until it is received, a random feature
+is worked on.
+
+Goals
+-----
+
+The primary model being worked on is the soft MMU target to be able to
+emulate the Shix 2.0 board by Alexis Polti, described at
+http://perso.enst.fr/~polti/realisations/shix20/
+
+Ultimately, qemu will be coupled with a system C or a verilog
+simulator to simulate the whole board functionalities.
+
+A sh4 user-mode has also somewhat started but will be worked on
+afterwards. The goal is to automate tests for GNAT (GNU Ada) compiler
+that I ported recently to the sh4-linux target.
+
+Registers
+---------
+
+16 general purpose registers are available at any time. The first 8
+registers are banked and the non-directly visible ones can be accessed
+by privileged instructions. In qemu, we define 24 general purpose
+registers and the code generation use either [0-7]+[8-15] or
+[16-23]+[8-15] depending on the MD and RB flags in the sr
+configuration register.
+
+Instructions
+------------
+
+Most sh4 instructions have been implemented. The missing ones at this
+time are:
+  - FPU related instructions
+  - LDTLB to load a new MMU entry
+  - SLEEP to put the processor in sleep mode
+
+Most instructions could be optimized a lot. This will be worked on
+after the current model is fully functional unless debugging
+convenience requires that it is done early.
+
+Many instructions did not have a chance to be tested yet. The plan is
+to implement unit and regression testing of those in the future.
+
+MMU
+---
+
+The MMU is implemented in the sh4 core. MMU management has not been
+tested at all yet. In the sh7750, it can be manipulated through memory
+mapped registers and this part has not yet been implemented.
+
+Exceptions
+----------
+
+Exceptions are implemented as described in the sh4 reference manual
+but have not been tested yet. They do not use qemu EXCP_ features
+yet.
+
+IRQ
+---
+
+IRQ are not implemented yet.
+
+Peripheral features
+-------------------
+
+  + Serial ports
+
+Configuration and use of the first serial port (SCI) without
+interrupts is supported. Input has not yet been tested.
+
+Configuration of the second serial port (SCIF) is supported. FIFO
+handling infrastructure has been started but is not completed yet.
+
+  + GPIO ports
+
+GPIO ports have been implemented. A registration function allows
+external modules to register interest in some port changes (see
+hw/tc58128.[ch] for an example) and will be called back. Interrupt
+generation is not yet supported but some infrastructure is in place
+for this purpose. Note that in the current model a peripheral module
+cannot directly simulate a H->L->H input port transition and have an
+interrupt generated on the low level.
+
+  + TC58128 NAND flash
+
+TC58128 NAND flash is partially implemented through GPIO ports. It
+supports reading from flash.
+
+GDB
+---
+
+GDB remote target support has been implemented and lightly tested.
+
+Files
+-----
+
+File names are harcoded at this time. The bootloader must be stored in
+shix_bios.bin in the current directory. The initial Linux image must
+be stored in shix_linux_nand.bin in the current directory in NAND
+format. Test files can be obtained from
+http://perso.enst.fr/~polti/robot/ as well as the various datasheets I
+use.
+
+qemu disk parameter on the command line is unused. You can supply any
+existing image and it will be ignored. As the goal is to simulate an
+embedded target, it is not clear how this parameter will be handled in
+the future.
+
+To build an ELF kernel image from the NAND image, 16 bytes have to be
+stripped off the end of every 528 bytes, keeping only 512 of them. The
+following Python code snippet does it:
+
+#! /usr/bin/python
+
+def denand (infd, outfd):
+    while True:
+        d = infd.read (528)
+        if not d: return
+        outfd.write (d[:512])
+
+if __name__ == '__main__':
+    import sys
+    denand (open (sys.argv[1], 'rb'),
+            open (sys.argv[2], 'wb'))
+    
+Style isssues
+-------------
+
+There is currently a mix between my style (space before opening
+parenthesis) and qemu style. This will be resolved before final
+integration is proposed.