The kernel contains the core components of the pinball operating system.
On the WPC platform, all of these modules are built into the fixed
portion of ROM, and do not require bank switching.  This is also where
all of the interrupt handlers for realtime processing can be found.

Core:
error.c - Handle system errors
idle.c - Idle-time processing
init.c - Initialization
log.c - Logging for debugging

Hardware control:
ac.c - AC zero-cross circuit
dmd.c - Dot matrix display
flip.c - Flippers
lamp.c - Lamps
segment.c - Segment displays
sol.c - Solenoids
sound.c - Sound board
switches.c - Switches
triac.c - Triacs for GI

Effects:
deff.c - Display effects
lamplist.c - Manage sets of lamps at a time
leff.c - Lamp effects

Display:
animation.c - Implement complex animation sequences
font.c - Write strings to the DMD
frame.c - Draw bitmaps to the DMD
printf.c - Build strings from printf() specifications

Other:
adj.c - Manage adjustables
audit.c - Chalk audits
bcd.c - Binary-coded decimal math
csum.c - Checksum protected memory
freetimer.c - Free-running timer APIs
game.c - Main pinball game state machine
ladder.c - Scoring rules
player.c - Switch in/out per-player variables
random.c - Random number generator
score.c - Basic scoring APIs
timedmode.c - Generic timed mode module
timer.c - Pausable timer APIs