Elements of Computing Systems Chapter 3

Preamble

• Welcome Sam
• Quick overview of the chapter
• DFF: primitive and possible implementations
• How do computer clocks actually work?
  • Capacitors and filters (Chris L)
  • Crystal with resonant frequency (James M)
• A cycle is from the beginning of a tick to the end of the tock
• How does the simulator’s clock work (Appendix A.7)
  • During a tick the inputs are read, on tock the outputs are set
• Tuning a clock cycle such that all part of the circuit can be reached
• Chips produce junk between ticks
• A DFF is effectively like a delay line
• The “invalid design” with fan-in 2 in Figure 3.1 is really a short circuit
  • The Mux both isolates the circuit and allows our behaviour
• Does a Latch relate to flip-flops?
  • Wikipedia page is fairly revealing
• Addressing is introduced without too much foreshadowing of how it’ll be used later on
• Multiplexers are about where something goes our load pins are about when
• A brief conversation about the meaning of k in 3.2.3

Build

• James M’s glorious rake task
• Turns out you do have to declare out twice in the HDL
• TextMate beats Jamie’s Vim on this round
• For addressing, we refer back to our n-way (de)muxes from chapter 1
• We use the 3 most significant address bits in our RAM64 to select the RAM8 then we pass the rest
  • Comparable with paging
  • Tree-like approach as smaller chunks of the address are sent down branches
• RAM16K isn’t as big a jump in size as the previous ones, tripped us up
• In x86 we read a word of 32 bits then take a byte out of that
  • The minimum addressable size is 32 bits
  • Boundary alignments are important for performance (to explore)
• Order of precedence was a point of debate on the program counter
• Does PC need load and reset?

Any other business

January's meet-up will be at Go Free Range's office on Tuesday, 13th January.

Turns out enough people have ordered copies of the book through the referral code that we have enough to buy a hard copy for the club.

We took a cheeky look at Chapter 4 to see how things will progress in the new year.