Re: [Qemu-devel] [PATCH 14/17] lm32: todo and documentation

[Blue Swirl]

On Fri, Feb 11, 2011 at 1:12 AM, Michael Walle <address@hidden> wrote:
> This patch adds general target documentation and a todo list.
>
> Signed-off-by: Michael Walle <address@hidden>
> ---
>  target-lm32/README |   46 ++++++++++++++++++++++++++++++++++++++++++++++
>  target-lm32/TODO   |    3 +++
>  2 files changed, 49 insertions(+), 0 deletions(-)
>  create mode 100644 target-lm32/README
>  create mode 100644 target-lm32/TODO
>
> diff --git a/target-lm32/README b/target-lm32/README
> new file mode 100644
> index 0000000..a1c2c7e
> --- /dev/null
> +++ b/target-lm32/README
> @@ -0,0 +1,46 @@
> +LatticeMico32 target
> +--------------------
> +
> +General
> +-------
> +All opcodes including the JUART CSRs are supported.
> +
> +
> +JTAG UART
> +---------
> +JTAG UART is routed to a serial console device. For the current boards it
> +is the second one. Ie to enable it in the qemu virtual console window use
> +the following command line parameters:
> +  -serial vc -serial vc
> +This will make serial0 (the lm32_uart) and serial1 (the JTAG UART)
> +available as virtual consoles.
> +
> +
> +Programmatically terminate the emulator
> +----------------------------------------
> +Originally neither the LatticeMico32 nor its peripherals support a
> +mechanism to shut down the machine. Emulation aware programs can write to a
> +to a special register within the system control block to shut down the
> +virtual machine.  For more details see hw/lm32_sys.c. The lm32-evr is the
> +first BSP which instantiate this model. A (32 bit) write to 0xfff0000
> +causes a vm shutdown.
> +
> +
> +Special instructions
> +--------------------
> +The translation recognizes one special instruction to halt the cpu:
> +  and r0, r0, r0
> +On real hardware this instruction is a nop. It is not used by GCC and
> +should (hopefully) not be used within hand-crafted assembly.
> +Insert this instruction in your idle loop to reduce the cpu load on the
> +host.

It would be better to use MMIO or privileged instruction for this
instead of changing an unprivileged instruction.