(notes) 2023-08-21 - Add section brainstorming a revised memory-map + initial Instruction Pointer

notes/2023-08-21--dev-notes.md

@@ -6,15 +6,41 @@
   - [x] graphics: 80 col card template
   - see below
 - printing
-  - [ ] print: paper tape template
-  - [ ] print: colour coding forms
-  - [ ] print: 80 col card template
+  - [x] print: paper tape template
+  - [x] print: colour coding forms
+  - [x] print: 80 col card template
 
 - [ ] see code/design commentary below...
 
 - (consider python (microbit) version of simulator)
   - maybe ask for e's input
 
+## Memory map re-think
+
+### CPU start-up
+
+When starting up, the CPU executes a `JMP $FF`.
+
+Put differently: it starts executing instructions at the address contained in `$FF`.
+
+### Cardiograph memory map
+
+```
+00-19 - display (5x5)
+1A    - pointer to display memory
+1B    - keypad: value of latest key pressed
+1C    - reserved for future use (bank switching flag)
+1D-FE - free
+```
+
+## References re: where do CPU instruction pointers start, and how are they set?
+
+- ["Memory Map Requirements", in *6502 PRIMER: Building your own 6502 computer*](http://wilsonminesco.com/6502primer/MemMapReqs.html)
+  - "Reset (RST):  When the 6502's RST input gets pulled low and then brought back high, the 6502 starts its reset process, and gets the address to start executing program instructions from $FFFC-FFFD.  Notice it does not start executing at address $FFFC, but reads it to get the beginning address of the routine where it should start executing.  That routine will normally have to be in ROM."
+- [What address does the x86 begin executing at?](https://stackoverflow.com/questions/4004493/what-address-does-the-x86-begin-executing-at)
+  - "The `cs` (code selector) register is set to `0xffff` and `ip` (instruction pointer) is set to `0x0000`."
+- [Why is the first BIOS instruction located at 0xFFFFFFF0 ("top" of RAM)?](https://superuser.com/questions/988473/why-is-the-first-bios-instruction-located-at-0xfffffff0-top-of-ram) (x86)
+
 ## Imported notes from earlier
 
 ### 2023-08-18 cardiograph loose thoughts