From 142c8f430c310dab96ceb1798b0bfee94d50563c Mon Sep 17 00:00:00 2001
From: Alan Cox <alan@linux.intel.com>
Date: Thu, 15 Sep 2016 21:02:27 +0100
Subject: [PATCH] nc100: updates - basics of suspend/resume NMI path and some
 cleaning

---
 Kernel/platform-nc100/README      |   3 -
 Kernel/platform-nc100/bootblock.s |  42 +++++++++++
 Kernel/platform-nc100/nc100.s     | 121 +++++++++++++++++++++++++++++-
 3 files changed, 159 insertions(+), 7 deletions(-)

diff --git a/Kernel/platform-nc100/README b/Kernel/platform-nc100/README
index 469f1cfa..09fcfe09 100644
--- a/Kernel/platform-nc100/README
+++ b/Kernel/platform-nc100/README
@@ -44,9 +44,6 @@ resulting nc100.cim as the bootscript for the emulator.
 
 TODO
 
-- baud rate/serial mode setting
-- RTC (note: the RTC only works 1900-1999 so must be rejigged to get it to
-  work 1990 - 2099)
 - driver for the power status bits
 - lots of testing
 - control doesn't seem to work ???
diff --git a/Kernel/platform-nc100/bootblock.s b/Kernel/platform-nc100/bootblock.s
index e9d62082..2d40a554 100644
--- a/Kernel/platform-nc100/bootblock.s
+++ b/Kernel/platform-nc100/bootblock.s
@@ -5,8 +5,50 @@
 ;	FIXME: we need a valid NMI vector in the low 0x100 at all times
 ;
 
+;
+;	These must match the actual nc100.s code
+;
+entry_so	.equ 0x1BE
+kernel_sp	.equ 0x1C0
+resume_vector	.equ 0x1C2
+suspend_map	.equ 0x1C4
+entry_banks	.equ 0x1C8
+suspend_stack	.equ 0x1FE
+
+		.org 0xE0
+;
+;	Stub to switch into the resume bank and code
+;
+		out (0x13),a
+		jp (hl)
+;
+;	We are assembled for 0x100 but actually load at 0xC000 initially
+;	but will relocate ourselves.
+;
 		.org 0x100
 		di
+	        ld (entry_sp),sp
+                ld hl, (0xB000)	; Save MMU bank copies from the OS
+	        ld (entry_banks),hl
+	        ld hl, (0xB002)
+	        ld (entry_banks+2),hl
+		;
+		;	Resume or new ?
+		;
+	        ld hl,(resume_vector)
+	        ld de,#0
+	        ld (resume_vector),de
+	        ld a,h
+	        or l
+	        jr z, no_resume
+;
+;	We want to put our suspend page back at 0xC000 but we can't do that
+;	directly as we are right now executing that bank
+;
+	        ld a,(suspend_map + 3)
+	        jp 0xE0		; stub to bank switch and jp
+
+no_resume:
 		ld a, 0x83	; map the low 16K of the kernel
 	        out (0x10), a
 		ld hl, 0xC000	; copy ourself into the low 16K
diff --git a/Kernel/platform-nc100/nc100.s b/Kernel/platform-nc100/nc100.s
index ee72c7d2..72662504 100644
--- a/Kernel/platform-nc100/nc100.s
+++ b/Kernel/platform-nc100/nc100.s
@@ -153,11 +153,120 @@ _program_vectors:
             ld (0x0001), hl
 
             ld (0x0066), a  ; Set vector for NMI
-            ld hl, #nmi_handler
+            ld hl, #my_nmi_handler
             ld (0x0067), hl
-	    jr map_kernel
+	    jp map_kernel
 
 ;
+;	These are shared and agreed with the bootstrap code in the
+;	bootstrap low page
+;
+entry_sp     .equ 0x1BE
+kernel_sp   .equ 0x1C0
+resume_vector .equ 0x1C2
+suspend_map .equ 0x1C4
+entry_banks .equ 0x1C8
+suspend_stack .equ 0x1FE
+
+suspend_r:   .db 0
+
+my_nmi_handler:
+	    push af
+	    xor a
+	    jr suspend_1
+	    push af
+suspend:
+	    ld a,#1
+suspend_1:
+	    ld (suspend_r),a
+	    ld a,i
+	    push af
+	    di
+	    ld a,#0x80
+	    out (0x10),a
+	    ; Save our SP
+	    ld (kernel_sp), sp
+	    ld sp,#suspend_stack
+	    push bc
+	    push de
+	    push hl
+	    push ix
+	    push iy
+	    exx
+	    push bc
+	    push de
+	    push hl
+	    ex af,af'
+	    push af
+	    ; Register map saved
+	    ld hl,#suspend_map
+	    call save_maps
+	    ld hl,#resume
+	    ld (resume_vector),hl
+	    ld de,(suspend_r)
+	    ; Now switch the low 48K (OS) banks back as they were
+	    ; and run the "official" OS NMI handler
+	    ld hl,(entry_banks)
+	    ld sp,(entry_sp);
+	    ld a,l
+	    out (0x10),a
+	    ld a,h
+	    out (0x11),a
+	    ld a,(entry_banks+2)
+	    out (0x12),a
+	    ld a,e
+	    or a
+	    jr z, nmi_and_resume
+	    ; Hand triggered suspend
+	    ld a,(entry_sp)
+	    ; To NC100 OS
+	    ret
+nmi_and_resume:
+	    call 0x66
+;
+;	Called by the booter via our resume vector. The bootstrap or ROM has
+;	already set the high 16K correctly before calling us there
+;
+resume:
+	    ld hl,#0
+	    ld (resume_vector),hl
+	    ld hl,#suspend_map+1
+	    ; Begin by restoring the mapping for 0x4000-0xBFFF
+	    ld a,(hl)
+	    out (0x11),a
+	    inc hl
+	    ld a,(hl)
+	    out (0x12),a
+	    ; Map the bootstrap bank back in at 0x0000-0x3FFF so we can get
+	    ; our data back
+            ld a,#0x80
+	    out (0x10),a
+	    ; Restore the registers
+	    ld sp,#suspend_stack-36
+	    pop af
+	    ex af,af
+	    pop hl
+	    pop de
+	    pop bc
+	    exx
+	    pop iy
+	    pop ix
+	    pop hl
+	    pop de
+	    pop bc
+	    ; Switch back to the kernel stack pointer. This could be in any
+	    ; bank so we must not dereference it until we fix the low 16K
+	    ld sp,(kernel_sp)
+	    ; Grab the low 16K mapping we had before
+	    ld a,(suspend_map)
+	    out (0x10),a	; booter page in 0x0000-0x3FFF vanishes here
+				; and our vectors re-appear
+	    pop af		; IRQ state
+	    jp po,no_irq_on
+	    ei
+no_irq_on:  pop af
+	    ret
+;
 ;	Userspace mapping pages 7+  kernel mapping pages 3-5, first common 6
 ;
 ;
@@ -222,6 +331,12 @@ map_save:
 	    push hl
 	    push af
 	    ld hl, #map_savearea
+	    call save_maps
+	    pop af
+	    pop hl
+	    ret
+
+save_maps:
 	    in a, (0x10)
 	    ld (hl), a
 	    inc hl
@@ -233,8 +348,6 @@ map_save:
 	    inc hl
 	    in a, (0x13)
 	    ld (hl), a
-	    pop af
-	    pop hl
 	    ret
 
 map_savearea:
-- 
2.34.1