AutoConfig
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AutoConfig is a feature of Amiga computers which is analogous to PCI configuration.
When the computer is switched on, AmigaOS interrogates each expansion slot in turn and automatically allocates each expansion card resources, i.e. address space, depending on what is installed in the slot. In the case of a memory card, the OS would also add the memory to the available system memory.
How it works
Expansion devices respond to certain fixed memory addresses starting at $E80000 if the /CFGIN signal is asserted and the device is not already configured. The CPU reads nibbles of configuration information (usually supplied by a PAL) such as manufacturer ID, product ID, and the amount of address space the device requires. The CPU then writes a base memory address to the device (or tells it to "shut up" if for some reason it can't be configured), and the device asserts /CFGOUT.
The /CFGIN of the first device is tied to ground. The second device's /CFGIN is controlled by the first device's /CFGOUT, and so on.
In a backplane design such as the A2000, connecting the /CFGOUT of one slot directly to the /CFGIN of the next would create the problem that an unoccupied slot would break the configuration chain. To solve this, the backplane ORs the /CFGIN and /CFGOUT signals to form the /CFGIN for the next slot (/CFGOUT is pulled low if undriven), which allows empty slots to be bypassed. This requires one 74LS32 (quad OR gate) on the A2000.
References
- Miner, Jay et al (1991). Amiga Hardware Reference Manual: Third Edition. Addison-Wesley Publishing Company, Inc. ISBN 0-201-56776-8.
External links
- Why Amigas are great computers (http://www.cleverstuff.net/pers/amigawhy.html)it:AutoConfig