;/*  os_cpu.h
; *
; *	Motorola Coldfire MCF5307 port to MicroC/OS-II
; *
; *  Ross Berteig
; *  Cheshire Engineering Corp
; *  650 Sierra Madre Villa, Suite 201
; *  Pasadena  CA 91107
; *  +1-626-351-5493       +1-626-351-8645 FAX
; *  Ross@CheshireEng.com, www.CheshireEng.com
; *
; *  Copyright (C) 1998 Cheshire Engineering Corporation.
; *  Based on a port to uCOS version 1.x by David Fiddes.
; *  Portions Copyright (C) 1997 David Fiddes, D.J.Fiddes@hw.ac.uk
; *  Anything that no longer works is probably not his fault.
; */
;
;
;  A note for the interested:
;
;  David uses the movem.l (a7),d0-d7/a0-a6, lea 60(a7)a7	     
;  construct in place of the traditional 68xxx		    
;  movem.l (a7)+,d0-d7/a0-a6. It is perfectly in order to	    
;  push/pop individual registers using movem.l (a7)+,d2 , etc.   
;  but it's a bit slower (and more verbose)			    
;								    	    
;  The lea instruction is required because the ColdFire can't    	    
;  push multiple registers directly to the stack...		    	    
;
	    .text
	    .global _OSStartHighRdy
	    .global _OSCtxSw
	    .global _OSIntCtxSw
	    .global _OSTickISR
	    .global _CPUFormatError

	    .extern  _OSIntEnter
	    .extern  _OSIntExit
	    .extern  _OSTimeTick
	    .extern  _OSTCBCur
	    .extern  _OSTCBHighRdy
	    .extern  _OSPrioCur
	    .extern  _OSPrioHighRdy
	    .extern  _OSTaskSwHook
	    .extern  _OSRunning
	    
	    .extern  ___MBAR

;  Procedure : OSStartHighRdy				    
;								    
;  The procedure gets the highest priority task then loads its   
;  stack before restoring all of the registers and doing an RTE  
;  to actually start the task. Called directly from uC/OS	    
;
_OSStartHighRdy:
  jsr      _OSTaskSwHook		;Call the hook proc
  moveq    #1,d0
  move.b   d0,(_OSRunning)
  move.l   (_OSTCBHighRdy),a1		;Get highest prio. task
  move.l   (a1),a7			;Get ptr to top of stack

  movem.l  (a7),d0-d7/a0-a6		;Store all the regs
  lea	   60(a7),a7			;Advance the stack pointer

  rte					;Return to task



;  Procedure : OSIntCtxSw					    
;								    
;  The procedure is called by when the uC/OS wants to return to  
;  a different task at interrupt time. Used primarily within the 
;  timer tick interrupt.					    
;
;  Offset the stack pointer to get back to an exception frame, then
;  simply jump to OSCtxSw() to do the rest of the details.  We skip the
;  register save at the top of OSCtxSw() because the interrupt routine
;  itself has already saved all the registers in the right spot after
;  the exception frame.
;
;  The stack adjustment compensates for the following:
;
;    OSIntExit call				  4
;    OSIntExit stack frame adjust		  4 <- goes to 0 for -O2
;    OSIntCtxSw call				  4
;						--- 
;						 12 or 8
;  The DiabData compiler option -X36=1 will force the use of stack
;  frames regardless of the optimization settings. The default if 
;  any optimizations are on is to avoid a stack frame in any function
;  with no local variables on the stack.

_OSIntCtxSw:
   adda.l   #12,a7			; Compensate stack pointer
   bra CtxSwTail			; Handle the context switch,


;  Procedure : OSCtxSw					    
;								    
;  The procedure is installed as an interrupt handler and called 
;  using a TRAP instruction within the uC/OS scheduler to swap   
;  contexts at the task level.				    
;
;  Initialization must insert this routine into the vector table at
;  vector 46 (offset 0xb8) to correspond to the definition of the
;  OS_TASK_SW() macro in os_cpu.h as TRAP #14.

_OSCtxSw:
  lea	   -60(a7),a7
  movem.l  d0-d7/a0-a6,(a7)

CtxSwTail:
  move.l   (_OSTCBCur),a1		;Save stack ptr in TCB
  move.l   a7,(a1)

  jsr      _OSTaskSwHook		; Call the hook proc

  move.l   (_OSTCBHighRdy),a1		;Point to HI Prio. Task Rdy
  move.l   a1,(_OSTCBCur)		;This is now current TCB
  move.b   (_OSPrioHighRdy),d0		;And track the hi prio value
  move.b   d0,(_OSPrioCur)		;   as well for faster compares

  move.l   (a1),A7			;Get new task's stack ptr
  
  movem.l  (a7),d0-d7/a0-a6
  lea	   60(a7),a7

  rte					;Return to new task


;  Procedure : OSTickISR					    
;								    
;  The procedure is installed as the timer tick ISR and called   
;  each time TIMER1 on the MCF5307 reaches it's reference value. 
;  It stores the current context before calling the uC/OS int    
;  nesting logic and timer tick routine which can cause the	    
;  context to change. Use this as an example of how to write	    
;  ISRs in uC/OS.
;
;  Notice that all ISRs *must* leave the same stack context
;  at the time of the call to OSIntExit() since if a context
;  switch does occur, OSIntCtxSw() must be able to find this
;  frame.  This probably means that other ISRs which have
;  local variables and do more work should follow this model of
;  calling a worker function similar to OSTimeTick() so that
;  the exception stack frame is left undisturbed.			    
;
;  Initialization must insert this routine into the vector table at
;  the vector 24+level (offset 0x64 + 4*level) where level is the 
;  irq priority level assigned to the timer tick.  For example, 
;  assigning the timer to level 5 would correspond to vector 29 
;  at offset 0x74 in the table.  The level is assigned with the
;  ICR1 register in the SIM module.

_OSTickISR:
  lea	   -60(a7),a7
  movem.l  d0-d7/a0-a6,(a7)

  ;Reset the timer chip (hard coded Timer1.TER reg value - bad)
  move.l   #___MBAR+0x151,a0 
  move.b   #0x03,(a0)

  jsr	   _OSIntEnter
  jsr	   _OSTimeTick
  jsr	   _OSIntExit

  movem.l  (a7),d0-d7/a0-a6
  lea	   60(a7),a7
  rte


;  Procedure:  CPUFormatError
;
;  Exception handler for frame format errors, which should never 
;  happen unless some ISR fails to follow the rules and a context
;  switch attempts to do an RTE with A7 pointing to the wrong place.
;
;  This version simply halts the CPU.  A better response would be
;  to figure out the context of the fault and produce a diagnostic
;  message somewhere, but we are an embedded system...
;
;  Initialization must insert this routine into the vector table at
;  vector 14 (offset 0x38).

_CPUFormatError:
  nop					; breakpoint or patch fodder
  nop
  nop
  nop
  halt					; nothing else to do here