I love these die shot RE walkthroughs. This is such a weird choice though; almost no one used this chip for production hardware. The WD 17xx series was the king of floppy controllers in the 70's and early 80's (well, if you ignore Woz's masterpiece, which was discrete logic).<p>Seems like if you're going to reverse an obscure chip, something with a more exotic application would have been more fun?
The floppy drive controller chip costing and being better than the main CPU reminds me of some of my arduino projects.<p>For example I was driving a GSM Modem (over serial) which contained a comparatively advanced ARM SoC driving it.. from an AT Mega 8-bit micro that I was programming. It was great educationally, but kindof hilarious :)
A lot of special-purpose ICs are actually general-purpose processors with a mask ROM (or sometimes EEPROM, with interesting consequences), since writing the "firmware" for different functionality is easier than doing a whole "hard-coded" chip design --- the various USB-to-X adapters are one common example of this.
The decision to use this chip (vs the WD) in the BBC Micro made me wonder if there were other obvious-in-hindsight bad/weird/hackish choices in classic computer design?<p>The PC-AT's use of the keyboard controller to control A20 and CPU reset comes to mind.<p>Any others?
My guess is that, at some point, a manager at Acorn asked which disk controller would the engineers recommend and they, obviously joking, said "8271".<p>When they realized what they had done, it was too late.