Design of a microcontroller

Well, prepare yourselves now for one hell of a topic: the design of a microcontroller.

I've recently started getting into VLSI design and what not - intend to eventually make a startup off it - and I was wondering about playing around with designing a microcontroller.

So, what exactly goes into these things? Obviously, GP/IO and ADCs with a CPU core, along with various serial transceivers (UART, I2C, SPI, etc.), but how are the modules linked?

Here, let me come up with an example that will illustrate better - suppose I take a motherboard, and completely hack up the BIOS - would I be able to code a "program" or bootloader to that chip that would allow me to use a motherboard as a MCU? That is, could a routine computer CPU be commanded differently by that program memory to say, ignore IDE protocol and use the IDE ports as GP/IO?

I'd like to think microcontrollers are as simple as hooking up peripherals to the address and data lines of a CPU, but that'd be a pretty foolhardy assumption.

Anyone have experience or ever played around with concepts like this?

 

So this is an interconnect protocol somewhat analogous to standards like PCIe?

Ideally I'd try to design a bus protocol that breaks out an interface over multi-purpose pins for allowing connection of addressed external peripherals (after all, how many ADCs do you need? haha).

And you're right, I'd rather stick with something that has already been designed, drafted and tested rather than try and reinvent the wheel, as I don't have $20 million or a fab with which I can use to prototype devices on a whim.