I really like these chip-level teardowns. It&#x27;s fantastic to see how the code you write actually executes.<p>On the Newton we were short of code space, and with a 4MB ROM it was expensive (in bytes) to do &quot;long&quot; branches.<p>The ARM 610 we were using would fault on a &quot;never&quot; condition code (0xF....). So we replaced thousands of fat function calls each with a single 0xFxxxxxxx instruction that was dispatched by a simple fault handler; it was fast enough -- the ARM&#x27;s exception handling is really good -- and even though ARM Ltd. wasn&#x27;t willing to sanction what we were doing with their &quot;undefined behavior&quot; grey area, they weren&#x27;t going to change the handling of &quot;NV&quot; on the 610, and this worked well enough to ship the first few versions of the Newt.<p>(The 68000 had a similar thing going on; all instructions starting with 0xAxxx or 0xFxxx would trap, so we used them to compress calls in the ROM on the Atari ST).<p>Fortunately memory is a lot less dear these days. (One recent project I was writing firmware for, I had a conversation that went like:<p>H&#x2F;W engineer: &quot;Sorry, but we&#x27;re going to have to change the amount of memory the system has.&quot;<p>Me (apprehensive and internally ready to fight): &quot;Okay...&quot;<p>H&#x2F;W: &quot;Yeah, to save materials cost, we&#x27;ll have to double it.&quot;<p>Me: &quot;W00t?&quot;)