TODO

- fix Elite

- implement colour border
    - honour the colour in SNA format

- infer filename format (SNA, z80) from extension
    - drop format arg

DONE - find out which instruction is pausing
  - DJNZ error

DONE - jetpac works
  - just too fast
  - need to work on timings/t-states

  - maybe have single goro and 'wait until T-state X'?

    - yes, have main loop:
      - keep track of t-states
      - everything in terms of t-states
        - machine supplies intervals (in t-states) and callbacks (method callbacks on speccy obj)
        - speccy provides 50 Hz hw interrupt
          - that resets scan position
        - speccy provides per-byte interrupt http://www.zxdesign.info/vidparam.shtml 
          - which is NOP unless painting screen
        - returns number of t-states 'taken'
          - careful - if processor is halted, we don't want to account for these

- make screen refresh per-line and interleave t-states

- better LD tstate handling



DONE - keyboard handling:

  func keyboardByte(addrHi byte, keysDown []keys) byte
  is a pure func which can be tested :-)
  also, a 'key' is/should have an 'addr bit' and a 'data bit', and the above function
  is a fairly simple combination of those
    i.e. don't loop over all possible keys and see if they are depressed

- 256x256 memory visualiser
  - read/write/execute (RGB :-)


- "PRESS ANY KEY" in arnhem is running IN A, (0xFE)
  - which keyboard port should that read? all of them?

  - http://faqwiki.zxnet.co.uk/wiki/ZX_Spectrum_ULA
  "IN from port xxFE will read the keyboard state and tape input. Each bit of the high byte selects a keyboard half-row; that row is read if the bit is low. If a key is pressed on any selected half-row, the corresponding bit of the data byte is low; this accounts for bits d0–d4. d6 is the value at the EAR socket (polarity?); d5 and d7 are not used. "
    - so LD A, 0 : IN A, (0xfe) has all high byte bits low, reads all keyboard ports

- hanging loop is using HALT to wait for an interrupt
  - should interrupt return after HALT
  - and inspects system variable incremented during interrupt (FRAMES)

- hanging loop is reading from system variable FRAMES (0x5c78)
  which should be being updated every 20ms
  - BEEP code is doing DI, should that stop IM1 interrupt?

- add debugging hooks
  - callbacks or channels for execution info
  - and for control (set breakpt at addr X, single-step, set execution speed)

  - expose those channels/controls over http/json (websocket)

  - write debugging UI which drives http api
    - language/ui toolkit?

- post-process err output (equivalent to getting step-by-step debugging)
  to visualise or feed into a visualisation tool
  - or add call/ret tracing to emulator

- use debugger to work out what is going on with arnhem hang

- races:
  - if we want to remove them, we'd have to have screen refresh properly isolated
    (as well as keyboard?)
  - the correct way would be either a lock on peek/poke/peekbuf or an actor
    (r/w, addr)

- hang happens while running sound
  - with interrupts disabled
  - is there an NMI expected to break the loop?

- add IM 0

- add beep/border colour output port support

DONE - IM 2

- diagnose 'hang' when playing games
  - CPU is still running
  - look at before/after difference of hang
    - start with PC

- remove races

- add PC/mem visualisation
  - show memory
  - use watchfunc (need to add read/write flag, add to read)
  - reads and writes (decaying colour change? r == write g == read)
    - stack will look nice
    - different colour (b) for PC?

DONE - implement colour attributes

DONE - implement flash (every 32 refreshes)

DONE - sort out state setup/load (EI frigged in on Run)

- remove 'z80' from methods on file/z80 and make it an interface
  suitable for different load types

DONE - scale (3x) screen

DONE - saying 'n' to scroll causes exit

DONE - need to map 'backspace' key to something useful
  - perhaps map more convenience keys (e.g. ")
    - just do SDL key "backspace" depresses multiple spectrum keys

DONE - create a 'machine' interface
  - CP/M and Speccy
  - loaded by zog

- start on spectrum hardware
  DONE - add hardware interrupt hook
    - ei/di
    - im 0/1/2
  DONE - how does machine run interrupt?
    // load ROMs, start hardware (including interrupt goro, screen refresh)
    DONE - machine.Start(z)
  DONE - add keyboard IO ports
  - work out how to interrupt main loop to do screen refresh
  (happens progressively)
  DONE YES (maybe just have a 'tick' function to update screen)
  DONE (and call that in a time loop to start with)
  DONE - try loading a ROM
  DONE - will need read-only memory at some pt


- could trigger "which key is being pressed" from input handlers
  - will work better for games



- Fix remaining z80test problems
  DONE - ldi/ldir/etc
  - LD A, I : LD A, R
  - super ops

- add some kind of ULA interrupt to read memory and display image
  - use SDL to draw image

DONE - write spectrum-like print routines for z80test

- find (and remove boilerplate) of the F_Z/F_S etc setting

- zexall
  - huh. of course CRC is only compared at the end of the run, so don't know
  which instruction in the batch error'd the CRC...

  - bug:
    RES/SET use InstU8 hence set S+Z flags
    (CP uses explicit save/restore to avoid)

  - impl add/adc16 with same exec helper
    - see if it passes zexall adc


- performance
  - don't allocate an executeTrace in each instruction execution
  instead, re-initialise the slot in the haltTrace ring buffer
  (different re-init may have different perf characteristics. e.g. map is normally entry
  or small, may be worth scan+delete rather than re-alloc empty)

DONE - redo mem watches as callback
  - so can hook into ET without checking every instruction

- consider working labels in assembler
  - JP foo, JR foo, LD A, (foo)



  - grab a ROM and see where it dies! (spectrum-roms ubuntu pkg)
  - try and find some example programs
  - write a test rom/prelude of some kind
    - use it if cmdline to execute given

  DONE - CP/M has simple I/O for zexall
    - add 'zexall/cp/m support' option
      - write some Z80 assembly
      - drive an I/O port to write chars
        - register I/O handlers

- write enable-able logging streams (e.g. 'Z:' logging for locations)
  - tagged logging streams?

- spin up http server (gop?)
  - serve machine state (num cycles, registers, ...?) over http
  - ? serve zx spectrum display image over ws?


- emulator
  - implement some debug hook (zexall compatible)
    - conout to write to console
    - RST 16 :-)
    - jp 0 to "reboot cp/m"


  - zexdoc
  - zexall

- add cmdline disassembler
  - try on some big files
  - add (made up) labels for jump targets in disassembler
  - add some directives (org, data bytes)