[Qemu-devel] Embedded system simulation

[Bernhard Stegmaier]

Hi list,

for some private projects I tried out the feasability of simulating an  
ARM-based microcontroller including the on-chip peripherals using qemu.
Works great, currently I have a basic simulation of the  
microcontrollers UART via qemu's console.

Before I dig deeper into the more complex stuff (e.g., interrupt  
controller), I want to check if it's possible to also simulate the  
real (non-pc) hardware peripherals of my board (doesn't make much  
sense without).
The idea is that I create some external board-simulation-application  
talking to qemu, e.g., via a socket connection, and simulating  
behaviour of for example a spi device.

I think I have a somewhat clear picture on how to do this for  
synchronous communication (qemu peripheral simu writes a message to  
the socket, it's processed by the the board simu application, the  
response is sent back to the qemu simu, where some status registers,  
etc. of the peripheral can be set accordingly).
However, I currently have no idea of how to handle asynchronous stuff  
initiated by the board simu application (think of simulating pressing  
a button connected to an IO pin - the microcontroller application  
might just do an empty loop waiting for an interrupt without reading  
any memory registers and thus there is no point to hook in something  
reading from the board simu). I can think of some ugly solutions like  
creating a polling timer to check if there is something from the board  
simu app, but I don't really like that.
Ideally, I would like to implement some callback mechanism like it is  
done for getting input from the qemu-char stuff.

Can anybody give me some hints (or maybe even examples) on how to do  
this?
I already searched the list and looked into the qemu sources of qemu- 
char, but I didn't find anything being useful for me at first glance  
(or, I just didn't understand).
I found an older thread about a cosimulation setup similar to what I  
intend, but from the pieces posted there it's only using the  
synchronous stuff...


Thanks,
Bernhard