.area BOOTBLOCK (ABS)
-; NC200 entry point, when booting from floppy. We're paged in at 0x4000. This section
-; will get overwritten by vectors later but we don't care about that (it's only used
-; once on startup).
+; Stub to switch into the resume bank and code
+.org 0xE0
+ out (0x13),a
+ jp (hl)
- .org 0x0
-nc200_entry:
+; On entry, the map looks like this:
+; 0x0000: OS workspace
+; 0x4000: us (on the NC200 w/ floppy boot)
+; 0x8000: OS common
+; 0xc000: us (on either w/ PCMCIA boot)
+; We expect to run in the 0x0000 page, so the first thing we need to do is
+; remap ourselves.
+
+.org 0x100
di
ld a, #0x80
- out (0x13), a
- jp 0xc100
+ out (0x10), a ; map boot page to 0x0000
+ jp relocated
+relocated:
+ ; At this point the OS common page is in 0x8000-0xbfff.
+ ld (entry_sp),sp
+ ld sp, #suspend_stack
+ ld hl, (0xB000) ; Save MMU bank copies from the OS
+ ld (entry_banks),hl
+ ld hl, (0xB002)
+ ld (entry_banks+2),hl
- .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
+ ; Resume or new ?
+ ld hl, (resume_vector)
+ ld de, #0
+ ld (resume_vector), de
+ ld a, h
+ or l
+ jr z, no_resume
+
+; To resume, we map the suspend page at 0xc000 and jump to the resume
+; vector. As we're running from 0x0000, we can do that directly.
+
+ ld a, (suspend_map + 3)
+ out (0x12), a
+ jp (hl)
no_resume:
- ld a, #0x83 ; map the low 16K of the kernel
- out (0x10), a
- ld hl, #0xC000 ; copy ourself into the low 16K
- ld de, #0x0000
- ld bc, #0x4000
- ldir
- ld a, #0x84
- out (0x11), a
- ld a, #0x81
- out (0x12), a
- ld hl, #0x8000
- ld de, #0x4000
- ld bc, #0x4000
- ldir
- ld a, #0x85
- out (0x11), a
- ld a, #0x82
- out (0x12), a
- ld hl, #0x8000
- ld de, #0x4000
- ld bc, #0x4000
- ldir
- ld a, #0x84 ; map the other 32K of the kernel
- out (0x11), a
- ld a, #0x85
- out (0x12), a
- ld a, #0x86
- jp switch ; get out of the segment that is going to vanish
-switch: out (0x13), a ; map the common
- jp 0x0213 ; into crt0.s
+ ; We want to boot proper now. To do this, we need to copy the clean
+ ; copy of the kernel (in pages 0x80, 0x81, 0x82) into the working copy
+ ; (in 0x83, 0x84, 0x85).
+ ld a, #0x80
+ ld b, #0x83
+ call copy_page
+ ld a, #0x81
+ ld b, #0x84
+ call copy_page
+ ld a, #0x82
+ ld b, #0x85
+ call copy_page
+
+ ; Now map the working copy.
+ ld a, #0x83
+ out (0x10), a ; THIS IS SAFE because pages 0x80 and 0x83 contain the same code
+ inc a
+ out (0x11), a
+ inc a
+ out (0x12), a
+ inc a
+ out (0x13), a ; Page 0x86 contains the common.
+
+ ; And go.
+ jp 0x0213
+
+ ; Copies a single page. Source is in A, dest is in B.
+ ; Uses 0x4000 as the source and 0x8000 as the dest.
+copy_page:
+ out (0x11), a
+ ld a, b
+ out (0x12), a
+ ld hl, #0x4000 ; source
+ ld de, #0x8000 ; dest
+ ld bc, #0x4000 ; size
+ ldir
+ ret
.org 0x200
;
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