--- /home/strick/os9/one-nitros9/level1/modules/kernel/krn.asm	2023-03-10 21:18:41.143809366 -0800
+++ level1/modules/kernel/krn.asm	2023-07-01 23:07:27.951478057 -0700
@@ -1,7 +1,7 @@
 ********************************************************************
 * Krn - NitrOS-9 Level 1 Kernel
 *
-* $Id$
+* $Id: krn.asm,v 1.2 2023/07/02 06:07:27 strick Exp strick $
 *
 * This is how the memory map looks after the kernel has initialized:
 *
@@ -794,63 +794,74 @@
          ldb   #E$PrcFul
          rts
 
-FChain   bsr   L0543
-         bcs   L0531
-         orcc  #IntMasks
-         ldb   $0D,x
-         andb  #$7F
-         stb   $0D,x
-L0527    os9   F$AProc
-         os9   F$NProc
+FChain   bsr   DoChain     ; user mode F$Chain entry
+         bcs   chainErr     ; if err, branch
+*
+         ldu   <P$PModul,x  ; our primary module
+         os9   F$UnLink     ; unlink it
+*
+         orcc  #IntMasks   ; disable interrupts until rescheduled.
+         ldb   P$State,x   ; Fetch process state
+         andb  #^SysState  ; remove SysState flag.
+         stb   P$State,x   ; and save process state.
+reSched  os9   F$AProc     ; insert us onto active queue
+         os9   F$NProc     ; jump to scheduler (will not return here)
 
-SFChain  bsr   L0543
-         bcc   L0527
-L0531    pshs  b
-         stb   <P$Signal,x
+SFChain  bsr   DoChain     ; system mode F$Chain entry
+         bcs   chainErr
+*
+         ldu   <P$PModul,x  ; our primary module
+         os9   F$UnLink     ; unlink it
+*
+         bra   reSched
+chainErr pshs  b           ; on error from Linking or Loading: save error.
+         stb   <P$Signal,x ; puts error in exist status
          ldb   P$State,x
-         orb   #Condem
+         orb   #Condem     ; condemns the current process, because F$Chain cannot return!
          stb   P$State,x
-         ldb   #$FF
-         stb   P$Prior,x
-         comb
-         puls  pc,b
-L0543    pshs  u
-         ldx   <D.Proc
-         ldu   <P$PModul,x
-         os9   F$UnLink
-         ldu   ,s
+         ldb   #$FF        ; max priority,
+         stb   P$Prior,x   ;   so we release resources soon.
+         comb              ; sets carry.
+         puls  pc,b        ; and return with error from Linking or Loading.
+DoChain  pshs  u         ; stash U (users' SP)
+         ldx   <D.Proc      ; our process desc
+*
+*        ldu   <P$PModul,x  ; our primary module
+*        os9   F$UnLink     ; unlink it (too soon!?)
+*
+         ldu   ,s        ; restore users's SP into U
          bsr   L0553
-         puls  pc,u
-L0553    ldx   <D.Proc
+         puls  pc,u      ; restore U and return
+L0553    ldx   <D.Proc   ; subr called by both chain and fork:
          pshs  u,x
-         ldd   <D.UsrSvc
+         ldd   <D.UsrSvc ; reset: use UsrSvc for all 3 SWIs.
          std   <P$SWI,x
          std   <P$SWI2,x
          std   <P$SWI3,x
          clra
          clrb
-         sta   <P$Signal,x
-         std   <P$SigVec,x
-         lda   R$A,u
-         ldx   R$X,u
-         os9   F$Link
-         bcc   L0578
-         os9   F$Load
-         bcs   L05E7
-L0578    ldy   <D.Proc
-         stu   <P$PModul,y
-         cmpa  #Prgrm+Objct
-         beq   L058B
-         cmpa  #Systm+Objct
-         beq   L058B
-         comb
-         ldb   #E$NEMod
+         sta   <P$Signal,x  ; reset: no pending signal
+         std   <P$SigVec,x  ; reset: no signal vector
+         lda   R$A,u        ; lang/type code desired
+         ldx   R$X,u        ; desired module or filename
+         os9   F$Link       ; link desired module
+         bcc   L0578        ; (skip if good)
+         os9   F$Load       ; ... or load desired filename 
+         bcs   L05E7        ; but if error, "puls x,u,pc" with Carry & B set.
+L0578    ldy   <D.Proc      ; if was successful,
+         stu   <P$PModul,y  ; get our primary module again, into U.
+         cmpa  #Prgrm+Objct ; if a normal program is desired,
+         beq   L058B        ;   good
+         cmpa  #Systm+Objct ; else if a system object is desired,
+         beq   L058B        ;   good
+         comb               ; else bad:
+         ldb   #E$NEMod     ;   error "non existing module"
          bra   L05E7
 L058B    leay  ,u                      Y = addr of module
          ldu   2,s                     get U off stack (caller regs)
-         stx   R$X,u
-         lda   R$B,u
-         clrb
+         stx   R$X,u        ; update R$X advanced past name? why?
+         lda   R$B,u        ; desired size of area, in 256-byte pages.
+         clrb               ; D has desired size of area, in bytes.
          cmpd  M$Mem,y                 compare passed mem to module's
          bcc   L059B                   branch if less than
          ldd   M$Mem,y