Since Chris is busy with his RL, I will continue his blog entry about Star Castle Developments here.
 
Source code can be found here.
 
Note: There are still some occasional glitches which I have to sort out. And maybe even a crash. So if you find one, please let me know. Especially if you can reproduce it.
 
Attached is the final build from October 2015 and here the (never ending) DONE and TODO list:

; Explanation:
; - = open
; o = partially
; + = done
; ? = debatable
; x = cancelled

; Arcade Differences:
; - 3..6 lives via dip switches
; x extra lives > 100
; + game speed increases with score, segments, time...?
;.. + gamespeed (0..7) now based on score (increases every 2000 points)
; + ring rotation
;.. + not in sync
;.. + direction moves with ring (TODO: check mines on rings, gun gaps)
;.. + speed moves with the ring
;.. + speeds
;.... + increases with score (not castle)
;.... + reverse rotation at constant speed: 4.7s/loop, (1st castle: middle)
;.... + others: 0..1250 pts: 4.7 (outside)/3.2s (inside); ..2500 pts: 3.2/2.35s; then: 2.4/1.9s
;...... own speed range defined
;.. + offsets are transfered with the expanding rings
;.. o hit sparks (TODO: graphics)
; + killing gun and getting killed costs one life
; + shield kick
;.. + ignores previous speed
;.. + gives new speed
;.. + doesn't reposition
; o ships
;.. + facing left at life start
;.. + start position moves up with each new life? (10 positions, 1st one seems random, 2nd one is bottom + 1?)
;.. ? X and Y speed are NOT linked together
;.. o deceleration is linear and lower
;.. + ship decelerates differently in left/down (100%) than in right/up (~50%) direction!!!
;.. + after castle completed, ship continues at current spot in next castle
;.. + ship bounces during explosion
; o mines
;.. + immediate respawn
;.. + spawn position depends on gun direction (dir - 90°)
;.. + spawn independent from ship direction
;.. o hop back and forth on the rings
;.. + higher homing speed at higher scores (as fast as player's ship)
;.. + homing mine movement has some randomness to prevent mine grouping
;.. + homing mine lifetime varies (lifetime counted on ring too, but only 50%)
;.. + slower turning speed in lower castles
;.. o mines hop much faster in arcade in higher levels
;.. - max. one mine per ring segment
;.. + disappear when they hit a ship
;.. + mines on ring do not kill ship
;.. o hit sparks (TODO: graphics)
; + gun
;.. + shots immediately when there is a gap
;.. x projectile moves a bit faster
;.. + projectile disappears when ship is hit
;.. x starts new gun life at last direction
;.. + starts next ship at last direction
;.. + shots whenever there is space, no matter where the player's ship is
;.. + is turning slower, especially initially
; + bullets
;.. + max. 3 at a time
; o sounds
;.. o siren frequency depending on segments (~65..260Hz):
;.... + intermediate screen (highest pitch, slightly higher than 3)
;.... + 36..28: 0 (lowest pitch)
;.... + 27..24: 1 (slightly higher)
;.... + 23..20: 2
;.... + 19..16: 3 (high pitch)
;.... + 15..12: 4 (reset to between 1 and 2)
;.... + 11.. 8..5 (slightly higher, still lower than 2)
;.... +..7.. 4..6 (slightly higher than 3)
;.... +..3......7 (slightly higher = intermediate)
;.. - homing mines sound
;.. + no sound when hitting segment first time
;.. + thrust sound very low
;.. - projectile sound starts with fire sound
;.. - better sound mapping
;.... - channel 0:
;...... + 2. ship explosion (channel 1?)
;...... + 8. siren
;.... - channel 1:
;...... + 1. gun explosion
;...... + 3. projectile
;...... + 6. bullet fire
;...... + 7. ship ring bounce
;...... + 9. thrust
;.... - both:
;...... + 4. mine hits
;...... + 5. sector hits (channel 0?)
;.... - homing mine sound
; + scoring: 10/20/30 points per segment hit (not per segment destroyed)
; + no leading zeroes
;.. + score
;.. + castle
;.. + ships
;.. + highscore
; ? scores are centered
; + digits are slightly wider
; - ...

; Bugs/TODOs:
; + it seems that the gun is correcting direction after finding a gap but before fireing
;.. this leads to shots going through intact sectors
; + increase vertical screen size (TODO: use gained time)
;.. + define extra stars data
;.. + adjust stars in various screens
;.. + center/resize other screens
; + make ring 1 data ordered like ring 0 + 2 data
; + gun needs gaps in all three rings
; o General task management
;.. + allow individual tasks with priority and order
;.. o adjust parameters of tasks (check if they could be skipped)
; + regenerate if middle ring is empty (test arcade).
; + homing mines broken at higher castles (>=6)
; + explosion too slow (check again when CPU time is reduced!)
; + vector angle gives too coarse results
; + occasional glitch when mine is shot
; - bullet sometimes glitches when it hits (could be same problem as with initial mine?)
; + DIR_SEARCH
;.. x gap found a bit too early (counter clockwise)
;.. + no gap found when GUNDIR = 17
; + occasional reversed intermediate castle/ship graphics
; + first mine glitch (only if thrusting or fireing!?)
;.. resulted from following order: 1. x-pos mine; 2. create mine; 3. display mine
; + thrust sound corrupted
; + thrust sound set to lowest possible frequency and made 50% louder
; + siren twice as loud
; ? bullet/ring check may have flaws
; + occasional single pixel glitch on empty ring segments
; + another occasional single pixel glitch at start of new life (reason: odd without even rotate)
; + empty high score initials ... (instead of aaa)
; + difficulty switches fixed at start of game (4 different high score tables)
;.. o make different high socre tables identifialble (colors only so far)
; + stop gun shooting when ship is exploding
; o more ring colors
;.. + 8 different sets
;.. o define colors
; o mine graphics (maybe slower?)
; + thrust sound broken after gun explosion
; + occasional crash!!! (X used in CheckRegenerate)
; + fixed last color mode remembered
; o check PAL colors on real hardware
; o mine explosion graphics? (code done, graphics todo)
; + add "arcade" to the title graphics
; o pulse red part of the title graphics in sync with music
; + (c) 201*3* (fixed "3" font)
; x new ship must not start at blind gun spot (but arcade does too)
; + highlights in small letters M and W and score 4
; + adjusted flashing text on/off ratio
; x vary ship's thrust display frames %10 -> e.g. %101
; + white vertical line before highscore
; - more gun explosion animations
;.. o gain space
;.. o optimize overlapping
;.. - implement new data
; - ...

; Ideas:
; + transfer colors with rings too
;.. + gun changes color too, is that OK?
; - PAL50 timing option
; + smaller ship to allow better manouvering?
;.. + data (ship, ship + flames)
;.. + offset
;.. + reflection
;.. + projectile collision
; + use direction search for mine/bullet ring hits
; x using VDELP0 to move ship smoother vertically (not possible)
; ? reverse display of double hit segments (dotted = complete, full = hit once)
;.. o done, but is it a good idea?
; + increase some difficulties 1000 points earlier (kick chance, gun turning)
; x better do 16 difficulties for those?
; - reduce maximum ring rotatation speed (saves CPU time)
; + rename "Wave" into "Castle"
; ! adjust scanlines
;.. + AA logo
;.. + title
;.. - Melody load
;.. - hishscores
;.. + game
;.. + messages