Re: is sim/common documented anywhere?

[Mike Frysinger <vapier at gentoo dot org>]

On Wednesday 22 August 2012 19:41:42 DJ Delorie wrote:
> I've read through the comments and README.  Mostly what's missing is
> some guide to help tell people where to begin, what parts to worry
> about, and WHY you'd use any given piece.

yes, some of the fundamental pieces explaining how it all comes together is 
missing

> Example: how do I set up the chip's RAM/ROM regions? 

you use sim_core_attach to attach memory regions.  the mapmask allows you to 
set different permissions on it.  be aware that the sim currently has an issue 
when used in conjunction with gdb -- the read/write bits not only lock out the 
simulated code from accessing the region, but gdb too :(.

so you can't setup something like executable-only memory by specifying 
access_exec as then when you try to use `x` or `dis` from gdb, you'd get back 
an error -- the memory may not be read.  similarly, if you were to try to use 
`load` to load an executable with custom contents into that region you'd again 
get denied -- gdb is not allowed to write to it.

i mentioned this a while ago seeking ideas, but didn't get any response.

> Do I want them to be user-configurable?

yes.  the idea of the sim is two fold: provide simulation of the ISA with no 
SoC related details (peripherals/memory regions/etc...), and then t optionally 
provide support for common SoCs.

> If so, what's the best way to manage them?

check out sim-model.c.  this lets you specify --model on the command line to 
select different SoCs.  this sets up CPU_MODEL (cpu) which you can then parse 
in the early init phases of the sim (sim_open) to attach an appropriate set of 
memory regions based on the model.

you can also use SIM_AC_OPTION_DEFAULT_MODEL() in your configure.ac to select 
the default model for the sim if you want one.

if you have different ISAs to select between, you probably want to use --
architecture for that.

HTH
-mike

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