\chapter{Kernel Services and API}
\label{chp:kernserv}

This chapter describes and defines the interface that tasks use
to access the services of the OS kernel.

The services provided by the kernel are provided through the [[RST]]
calls of the Z80 processor.  There are 8 of these calls, as well
as an interrupt routine that the Z80 provides.  The interrupt
routine is used by the task switcher, and is described in
\S\ref{chp:isr}, however an overview of the 8 RST functions is
provided next.

Each of these start 8 bytes off from the previous, so we need to
be sure that we don't overwrite previous ones, as well as be sure
that we start each of them at the right location.  We can fill
these with five [[nop]]s, but instead, we'll use the [[.org]]
directive on following calls.  We just need to be sure that we
don't use more than 8 bytes for each of these.


%%%%%%%%%%%%%%%%%%%%
\section{RST 00H - Startup/Reboot}

This is the startup/reboot call.  This will setup the system and
restart it appropriately according to the initialization routines
as defined and implemented in \S\ref{chp:init}.
We will just call that routine from here.

The basic initialization starts off at [[0x0000]] in ROM.  This
doubles as the implementation for [[RST 00]].  So we need to be
sure that we are at [[0x0000]]. This simply jumps to the [[.startup]]
routine.  


<<RST 00 implementation>>=
.org 0x000
.reset00:			; RST 00 - Init
        jp .start
@



%%%%%%%%%%%%%%%%%%%%
\section{RST 08H - Semaphores}

Semaphore control

<<RST 08 implementation>>=
.org 0x0008
.reset08:			; RST 08 - Semaphore control
	ret
@


%%%%%%%%%%%%%%%%%%%%
\section{RST 10H - TBD}

TBD

<<RST 10 implementation>>=
.org 0x0010
.reset10: 			; RST 10 - TBD
	ret
@


%%%%%%%%%%%%%%%%%%%%
\section{RST 18H - TBD}

TBD

<<RST 18 implementation>>=
.org 0x0018
.reset18:			; RST 18 - TBD
	ret
@


%%%%%%%%%%%%%%%%%%%%
\section{RST 20H - TBD}

TBD

<<RST 20 implementation>>=
.org 0x0020
.reset20: 			; RST 20 - TBD
	ret
@


%%%%%%%%%%%%%%%%%%%%
\section{RST 28H - TBD}

TBD 

<<RST 28 implementation>>=
.org 0x0028
.reset28:			; RST 28 - TBD
	ret
@


%%%%%%%%%%%%%%%%%%%%
\section{RST 30H - TBD}

TBD

<<RST 30 implementation>>=
.org 0x0030
.reset30:			; RST 30 - TBD
	ret
@


%%%%%%%%%%%%%%%%%%%%
\section{RST 38H - VBlank handler}

VBLANK IRQ interrupt. This should never be called directly by a
task.  We will simply jump to the [[.isr]] function from here,
which sits after the below NMI handler, in ROMspace.

<<RST 38 implementation>>=
.org 0x0038
.reset38:			; RST 38 - Vblank Interrupt Service Routine
	jp	.isr
@



%%%%%%%%%%%%%%%%%%%%
\section{NMI handler}

We're not using an NMI in this implementation, but we'll leave this
here in case we want to use it in the future.
This sits at [[0x0066]], 38 bytes from the [[RST 38]] handler.  We're 
basically wasting this space, but we might come back later and fill it in
or just drop the NMI handler altogether.  Regardless, this handler is here
even though it's not used in Pac/Pengo hardware.

<<NMI implementation>>=
.org 0x0066
.nmi:				; NMI handler
	retn
@