From 7a3a2f0a56a1a3de3c0423084c16dc6fd2183d7d Mon Sep 17 00:00:00 2001
From: Tyler True <944067+sirocyl@users.noreply.github.com>
Date: Sun, 2 Jul 2023 05:28:50 -0400
Subject: [PATCH 1/3] uefix.s: add CHS mode

This should enable booting a sector payload from an FDD, and so enabling `-D FLOPPY` on the yasm line will switch to CHS drive logic.
---
 uefix.s | 61 +++++++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 49 insertions(+), 12 deletions(-)

diff --git a/uefix.s b/uefix.s
index 6e1edb5..8c583aa 100644
--- a/uefix.s
+++ b/uefix.s
@@ -16,21 +16,46 @@
     rep movsb
     jmp 0:start
 start:
-    mov ah, 0x42
-    mov si, packet
+; Both CHS and LBA code is present in the loader, as we have the free space
+; and switching between the two manually is a single-byte edit.
+%ifdef FLOPPY
+    jmp load.chs
+%else
+    jmp load.lba
+%endif
+
+load:
+.chs:
+    mov ah, 0x02 ; function, chs load sector
+    mov al, 1 ; count sectors
+
+    mov dl, 0 ; drive (0 = floppy A:, 1 = floppy B:, 8 = HDD C:)
+    mov dh, 0 ; head
+    mov cl, 1 ; sector
+    mov ch, 0 ; cylinder
+    mov bx, 0x7c00 ; buffer
     int 0x13
-    jc error
+    jc error.chs
+    jmp 0x7c00
+.lba:
+    mov ah, 0x42 ; function, lba extended load
+    mov si, lbapacket ; location of int13h/AH=42h arguments packet
+    int 0x13
+    jc error.lba
     jmp 0x7c00
-packet:
-    db 0x10
-    db 0
-    dw 1 ; count
-    dw 0x7c00, 0 ; buffer
-    dq 1 ; LBA
 
 error:
-    mov si, errmsg
+.lba:
+    mov si, errmsg.lba
+    jmp error.loop
+.chs:
+; TODO: some FDDs may be slow to start, and need to reset and reread
+; the sector, while the disk spins up. Implement code here to do so
+; three or four times, then go ahead and print the error message.
+    mov si, errmsg.chs
+    jmp error.loop
 .loop:
+; TODO: Read error numbers from BIOS return regs, and print them with errmsg.
     lodsb
     or al, al
     jz .done
@@ -43,13 +68,25 @@ error:
     jmp .done
 
 errmsg:
-    db "Disk error :(", 0
+.lba:
+    db "Forth: BIOS returns an LBA loader error.", 0
+.chs:
+    db "Forth: BIOS returns a CHS loader error.", 0
+
+lbapacket:
+    db 0x10
+    db 0
+    dw 1 ; count
+    dw 0x7c00, 0 ; buffer
+    dq 1 ; LBA
 
+blank:
     times 446 - ($ - $$) db 0
 
+mbrinfo:
     db 0 ; not active
     db 0, 1, 0 ; start CHS
-    db 0x42 ; type
+    db 0x7f ; partition type (0x7f: experimental)
     db 0, 1, 0 ; end CHS
     dd 1 ; start LBA
     dd 1 ; length

From 19df4025e2cfb6e168648703a1551df0045be5a6 Mon Sep 17 00:00:00 2001
From: Tyler True <944067+sirocyl@users.noreply.github.com>
Date: Sun, 2 Jul 2023 05:52:35 -0400
Subject: [PATCH 2/3] off by one error

Load the sector after the first one.
---
 uefix.s | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/uefix.s b/uefix.s
index 8c583aa..d54705f 100644
--- a/uefix.s
+++ b/uefix.s
@@ -31,7 +31,7 @@ load:
 
     mov dl, 0 ; drive (0 = floppy A:, 1 = floppy B:, 8 = HDD C:)
     mov dh, 0 ; head
-    mov cl, 1 ; sector
+    mov cl, 2 ; sector
     mov ch, 0 ; cylinder
     mov bx, 0x7c00 ; buffer
     int 0x13

From 5cf052708ce203384a981325d1788830e6c3fbdb Mon Sep 17 00:00:00 2001
From: Tyler True <944067+sirocyl@users.noreply.github.com>
Date: Wed, 5 Jul 2023 06:40:27 -0400
Subject: [PATCH 3/3] uefix.s: fix comment on drive numbers

---
 uefix.s | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/uefix.s b/uefix.s
index d54705f..73c1406 100644
--- a/uefix.s
+++ b/uefix.s
@@ -29,7 +29,7 @@ load:
     mov ah, 0x02 ; function, chs load sector
     mov al, 1 ; count sectors
 
-    mov dl, 0 ; drive (0 = floppy A:, 1 = floppy B:, 8 = HDD C:)
+    mov dl, 0 ; drive (0 = floppy A:, 1 = floppy B:, 80 = HDD C:)
     mov dh, 0 ; head
     mov cl, 2 ; sector
     mov ch, 0 ; cylinder