commit 4b65df05e17e1cce8d70a96e272fce9094989754
parent 8508adafee4c3aa2bff622b58d3d7a7ebda4acde
Author: Virgil Dupras <hsoft@hardcoded.net>
Date: Sat, 5 Nov 2022 17:30:22 -0400
i386: add BIOS poking tool
I'm trying to get Dusk to run on a old Pentium 75Mhz laptop and it's not quite
the SeaBIOS we have in QEMU...
Diffstat:
3 files changed, 88 insertions(+), 0 deletions(-)
diff --git a/Makefile b/Makefile
@@ -21,6 +21,10 @@ pc.img: dusk $(ALLSRCS)
dd if=/dev/zero of=$@ bs=512 count=2880
./dusk < buildpc.fs
+pcdbg.img: dusk $(ALLSRCS)
+ cp README.md $@ # we want to have some dummy contents to read during diag
+ ./dusk < buildpcdbg.fs
+
.PHONY: pcrun
pcrun: pc.img
qemu-system-i386 $(QEMU_FLAGS) -drive file=pc.img,$(QEMU_DRVOPTS)
diff --git a/buildpcdbg.fs b/buildpcdbg.fs
@@ -0,0 +1,4 @@
+f<< /xcomp/i386/pc/bootdbg.fs
+
+S" pcdbg.img" mountImage ( drv ) 0 org rot Drive :sec!
+bye
diff --git a/fs/xcomp/i386/pc/bootdbg.fs b/fs/xcomp/i386/pc/bootdbg.fs
@@ -0,0 +1,80 @@
+\ Tools to debug a PC at boot time.
+\ This boot from the MBR and pokes around.
+?f<< /asm/i386.fs
+1 to realmode
+
+$7c00 to binstart
+0 value lblstart
+0 value lblmsg
+0 value lblprinthex
+0 value lblstop
+0 value lblloop
+
+here to org $aa55 here $1fe + w!
+forward8 jmp, to lblstart
+pc \ list of messages, 4 chars each
+," DL StopGeo SectErr "
+
+pc to lblmsg \ si=idx
+ si 2 i) shl, ( x4 ) si ( pc ) i) add, cl 4 i) mov,
+ ah $0e i) mov, bx $0007 i) mov,
+ pc al si 0 d) mov, $10 int, si inc, cl dec, ( pc ) abs>rel jnz, ret,
+
+pc to lblprinthex \ al=num
+ ah $0e i) mov, bx $0007 i) mov,
+ ax push, al 4 i) shr,
+ al '0' i) add, al ':' i) cmp, forward8 jc, al 7 i) add, forward! $10 int,
+ ax pop, al $0f i) and,
+ al '0' i) add, al ':' i) cmp, forward8 jc, al 7 i) add, forward! $10 int,
+ ret,
+
+pc to lblstop si 1 i) mov, lblmsg abs>rel call, 0 jmp,
+lblstart forward!
+cli, cld, ax ax xor, es ax mov, ds ax mov, ss ax mov, sp $7c00 i) mov, sti,
+ax $0003 i) mov, $10 int, \ video mode 80x25
+si 0 i) mov, lblmsg abs>rel call,
+al dl mov, lblprinthex abs>rel call,
+
+\ If you want a hardcoded drive parameters, uncomment code below
+\ dl $80 i) mov,
+
+si 2 i) mov, lblmsg abs>rel call,
+dx push, ah 8 i) mov, $13 int, \ dh=numheads-1 cl&3f=sec per trk
+al dh mov, lblprinthex abs>rel call,
+al cl mov, lblprinthex abs>rel call,
+dx pop,
+\ Enough for the generic info. Now, what we'll do is read sectors into $8000,
+\ one sector at a time, and print the first 8 bytes of it. Then, we wait for a
+\ a key press and try to read the next sector,and again, and again.
+\ When we encounter an error, we reset the sector, inc the head, try again. If
+\ we have another error, we reset the head, inc the cylinder, try again. If we
+\ have an error, we stop.
+
+\ We begin at cylinder 0, head 0, sector 1
+cx $0001 i) mov, \ ch=cyl cl=sec
+dh dh xor, \ dh=head
+pc to lblloop
+ cx push, si 3 i) mov, lblmsg abs>rel call, cx pop,
+ al ch mov, lblprinthex abs>rel call,
+ al cl mov, lblprinthex abs>rel call,
+ al dh mov, lblprinthex abs>rel call,
+ al dl mov, lblprinthex abs>rel call,
+ bx $8000 i) mov,
+ ax $0201 i) mov, \ ah=read cmd al=read 1 sector
+ $13 int, forward8 jnc,
+ \ error
+ cx push, si 4 i) mov, lblmsg abs>rel call, cx pop,
+ cl 1 i) cmp, forward8 jz,
+ \ cl != 1, we need to reset cl and inc head
+ cl 1 i) mov, dh inc, lblloop abs>rel jmp,
+ forward!
+ \ cl=1, we need to reset head and inc cylinder
+ dh dh or, lblstop abs>rel jz, \ dh=0? we have a terminating error!
+ dh dh xor, ch inc, lblloop abs>rel jmp,
+ forward!
+ \ no error, inc sector and print
+ cl inc,
+ di 8 i) mov, si $8000 i) mov,
+ pc al si 0 d) mov, lblprinthex abs>rel call, si inc, di dec, abs>rel jnz,
+ ah ah xor, $16 int, \ read key press
+lblloop abs>rel jmp,
