[Qemu-discuss] Customizing emulated boards?

[Alexander Duff]

Hello,

I'm emulating routers running OpenWrt for ARM using the 
realview-eb-mpcore machine and I've run into the problem of not being 
able to create more than one NIC.  For what it's worth, when specifying 
that the NIC should be an smc91c111, qemu-system-arm -M 
realview-eb-mpcore says that this machine doesn't support that device.  
When the device is unspecified, it defaults to the smc91c111 once the 
machine is booted.  Every NIC after the first defaults to rtl8139, but 
emulation of the PCI bus is missing (I am unsure if it's missing due to 
the OpenWrt kernel built for ARM or something in QEMU) so these devices 
show in QEMU's monitor, but not on the guest.

Since it's a router, I would very much like to have more than one 
ethernet port.  I downloaded the QEMU source and looked through it to 
see how the devices are created and assigned.  In realview.c (lines 265 
through 281), I found the following code:

    for(n = 0; n < nb_nics; n++) {
        nd = &nd_table[n];

        if (!done_nic && (!nd->model ||
                    strcmp(nd->model, is_pb ? "lan9118" : "smc91c111") 
== 0)) {
            if (is_pb) {
                lan9118_init(nd, 0x4e000000, pic[28]);
            } else {
                smc91c111_init(nd, 0x4e000000, pic[28]);
            }
            done_nic = 1;
        } else {
            if (pci_bus) {
                pci_nic_init_nofail(nd, pci_bus, "rtl8139", NULL);
            }
        }
    }

So my understanding is that it checks to see if a NIC has been created.  
If it hasn't, it creates an smc91c111 NIC and maps it to 0x4e000000, 
then sets "done_nic" to 1 and creates all subsequent NICs as rtl8139 
devices.

So, I have the following questions:

1) Could I make my own customized board by more-or-less copying the 
realview.c file and changing this section so that the first 8 or so NICs 
(however many I can fit in that memory space) are smc91c111 devices and 
offset them by the space it takes (I want to say 16 but I'll double 
check first)?  The next address on the memory map is 0x4f00000000 (USB, 
which I don't need anyway).

2) Is there any documentation on programming a custom board?  In this 
case, I don't think I need it, but it would be good to have.  I 
apologize if I've missed it, there are a lot of moving parts in this 
endeavor.

3) Is there a simpler way to get more than one ethernet port on a 
virtualized ARM machine? I've been working on this for a long time and 
I'm afraid I'm getting tunnel vision and missing an obvious solution.

4) Is this the right mailing list?  I've never done this before, so I 
apologize if the dev mailing list would have been better.  If there's a 
better place to ask this question or if anyone can point me in the right 
direction, I would be grateful for that information.  I already posted 
on the OpenWrt forums and received 0 replies.

Thank you very much, and I appreciate any help I can get on this.

-Alex