Add new under construction system calls to the readme and change the one for loading files to accomodate them, move the disk parameters to the main namespace in anticipation of restructuring the disk operations with the addition of the new system calls, rewrite parts of system to remove essentially duplicate code, and rewrite the explanation of the file system in the readme.

2 years ago · b34b0ea74e
5 changed files with 129 additions and 108 deletions
--- a/README.MD
+++ b/README.MD
@ -1,9 +1,9 @@
 EttinOS
 =======

-EttinOS is a minimalist 16-bit DOS-like hobbyist operating system for
-the IBM Personal Computer and compatible machines. Its git repository
-can be found at https://ahti.space/git/crazyettin/EttinOS and that of
+EttinOS is a minimalist 16-bit hobbyist disk operating system for the
+IBM Personal Computer and compatible machines. Its git repository can be
+found at https://ahti.space/git/crazyettin/EttinOS and that of
 EttinOS-extra, a collection of programs for the system, at
 https://ahti.space/git/crazyettin/EttinOS-extra.

@ -39,13 +39,11 @@ The input system is inspired by typewriters. Typing a character
 overwrites the cursor location and the erase (=tab) key erases it. The
 space and backspace keys move the cursor.

-EttinOS assigns the drives letters from A to D and uses the FAT12 file
-system. The hidden and total sectors entries of the BIOS parameter
-block, the entire extended BIOS parameter block, file attributes, and
-the file access date are not supported and are ignored if present: as a
-result disk labels and subdirectories are not supported. Drive letters
-and file names are case-insensitive and the latter follow the 8.3
-format. Text files use CRLF line endings.
+EttinOS assigns the drives letters from A to D and uses a version of the
+MS-DOS 3.0 FAT12 file system (in actual use since 2.1) without support
+for file attributes and thus disk labels and subdirectories. Drive
+letters and file names are case-insensitive and the latter follow the
+8.3 format. Text files use CRLF line endings.

 Drives and files are specified as ([A-D]:) and ([A-D]:)FILENAME.EXT
 respectively. Specifying the current drive, indicated in the prompt, is
@ -53,11 +51,11 @@ optional.

 A command can be followed by arguments separated from eachother and the
 command with spaces. Extra spaces are ignored. Commands other than
-changing the drive are stored as external programs: the command for a
-program is its file specification without the extension.
+changing the current drive are stored as external programs: the command
+for a program is its file specification without the extension.

 Commands included in EttinOS:
-  * [A-D]:: Change the drive.
+  * [A-D]:: Change the current drive.
  * ECHO:   Print a message. Syntax: ECHO Message to be printed
  * HELLO:  Print "Hello world!".
  * LIST:   Print a list of the files on a drive. Syntax: LIST DRIVE
@ -80,7 +78,7 @@ has finished running.

 System calls:
  * Interrupt 0x20: Return to the shell.
-  * Interrupt 0x21: Input and output:
+  * Interrupt 0x21: String operations:
      * AH = 0x0: Print a string ending in a null from SI.
      * AH = 0x1: Read a string ending in a null of at most AL
                  characters to DI until a return.
@ -88,8 +86,25 @@ System calls:
                  CRLF.
      * AH = 0x3: Read a string ending in a null of at most AL
                  characters to DI until a return and print a CRLF.
+      * AH = 0x4: (Under construction) Convert a decimal string ending
+                  in a null at SI to a value in AL.
+      * AH = 0x5: (Under construction) Convert a value in AL to a
+                  decimal string ending in a null at DI.
+      * AH = 0x6: (Under construction) Convert a hexadecimal string
+                  ending in a null at SI to a value in AL.
+      * AH = 0x7: (Under construction) Convert a value in AL to a
+                  hexadecimal string ending in a null at DI.
  * Interrupt 0x22: Disk operations:
-      * AH = 0x0: Load a file named at SI as a string ending in a null
+      * AH = 0x0: (Under construction) Load the directory of a drive
+                  named at SI as a string ending in a null to the offset
+                  BX and store the error codes in AL:
+                    * AL = 0x0: Succesful load
+                    * AL = 0x1: Drive not found
+                    * AL = 0x2: Unable to read disk
+      * AH = 0x1: (Under construction) Store a directory at the offset
+                  BX to a drive named at SI as a string ending in a
+                  null.
+      * AH = 0x2: Load a file named at SI as a string ending in a null
                  to the offset BX and store the file size in CX and the
                  error codes in AL:
                    * AL = 0x0: Succesful load
@ -97,7 +112,7 @@ System calls:
                    * AL = 0x2: Unable to read disk
                    * AL = 0x4: File or command not found
                    * AL = 0x8: Not enough memory
-      * AH = 0x1: Save a file (under construction).
+      * AH = 0x3: (Under construction) Save a file.

 Known bugs
 ----------
--- a/src/BOOT.ASM
+++ b/src/BOOT.ASM
@ -23,6 +23,7 @@ mediadescriptor db 0xf0
 sectorsperfat   dw 0x9
 sectorspertrack dw 0x12
 heads           dw 0x2
+hiddensectors   dw 0x0

 %else

@ -37,10 +38,10 @@ mediadescriptor db 0xfd
 sectorsperfat   dw 0x2
 sectorspertrack dw 0x9
 heads           dw 0x2
+hiddensectors   dw 0x0

 %endif

-
 ;Setup
 ;Set the segments
 start:
--- a/src/LOADF.INC
+++ b/src/LOADF.INC
@ -16,8 +16,8 @@ push di

 ;Store the current drive and offset
 mov word [.pointer], bx
-mov dl, byte [drive]
-mov byte [.drive], dl
+mov dl, byte [curdrive]
+mov byte [drive], dl

 ;Change the drive if needed
 ;Check for a drive specification
@ -53,7 +53,7 @@ mov cx, 0x0
 jmp .done
 ;Change the drive
 .contchdrive:
-mov [.drive], dl
+mov [drive], dl
 ;Move to the file name
 add si, 0x2

@ -112,7 +112,7 @@ pop ax

 ;Load the disk description table
 ;Set the source
-mov dl, [.drive]
+mov dl, [drive]
 mov ch, 0x0
 mov dh, 0x0
 mov cl, 0x1
@ -136,48 +136,48 @@ jmp .done
 ;Store the disk values used for the rest of the call
 .storevalues:
 mov ax, [buffer + 0xb]
-mov [.sectorsize], ax
+mov [sectorsize], ax
 mov al, [buffer + 0xd]
-mov [.clustersize], al
+mov [clustersize], al
 mov ax, [buffer + 0xe]
-mov [.reservedsectors], ax
+mov [reservedsectors], ax
 mov al, [buffer + 0x10]
-mov [.fats], al
+mov [fats], al
 mov ax, [buffer + 0x11]
-mov [.rootentries], ax
+mov [rootentries], ax
 mov ax, [buffer + 0x16]
-mov [.sectorsperfat], ax
+mov [sectorsperfat], ax
 mov ax, [buffer + 0x18]
-mov [.sectorspertrack], ax
+mov [sectorspertrack], ax
 mov ax, [buffer + 0x1a]
-mov [.heads], ax
+mov [heads], ax

 ;Calculate and store variables not found in the BPB
 ;Start of the root
 mov ah, 0x0
-mov al, [.fats]
-mul word [.sectorsperfat]
-add ax, [.reservedsectors]
-mov [.rootstart], ax
+mov al, [fats]
+mul word [sectorsperfat]
+add ax, [reservedsectors]
+mov [rootstart], ax
 ;Size of the root in sectors
-mov ax, [.rootentries]
+mov ax, [rootentries]
 mov dx, 0x20
 mul dx
 mov dx, 0x0
-div word [.sectorsize]
-mov [.rootsectors], ax
+div word [sectorsize]
+mov [rootsectors], ax
 ;Start of data
-add ax, [.rootstart]
-mov [.datastart], ax
+add ax, [rootstart]
+mov [datastart], ax

 ;Load the root
 ;Set the source
-mov ax, [.rootstart]
+mov ax, [rootstart]
 ;Set the destination
 mov si, buffer
 mov bx, si
 ;Set the size
-mov cx, [.rootsectors]
+mov cx, [rootsectors]
 ;Store the source and the loop counter in the stack
 .loadrootsector:
 push ax
@ -194,7 +194,7 @@ pop cx
 pop ax
 ;Set the next sector
 add ax, 0x1
-add bx, word [.sectorsize]
+add bx, word [sectorsize]
 ;Load the next sector
 loop .loadrootsector

@ -202,7 +202,7 @@ loop .loadrootsector
 ;Set DI to the root
 mov di, buffer
 ;Set the number of root entries
-mov cx, word [.rootentries]
+mov cx, word [rootentries]
 ;Set the entry pointer
 mov ax, 0x0
 ;Store the loop counter in the stack
@ -238,8 +238,8 @@ cmp word [di + 0x13], 0x0
 jne .sizerror
 ;Get the cluster size in bytes
 mov ah, 0x0
-mov al, [.clustersize]
-mul word [.sectorsize]
+mov al, [clustersize]
+mul word [sectorsize]
 mov bx, ax
 ;Store the file size
 mov ax, [di + 0x11]
@ -267,12 +267,12 @@ jmp .done
 mov ax, [di + 0xf]
 mov [.cluster], ax
 ;Set the source
-mov ax, [.reservedsectors]
+mov ax, [reservedsectors]
 call .calcsource
 ;Set the destination
 mov bx, buffer
 ;Set the size
-mov ax, [.sectorsperfat]
+mov ax, [sectorsperfat]
 ;Load the FAT
 mov ah, 0x2
 int 0x13
@ -282,13 +282,13 @@ int 0x13
 ;Set the source
 mov ax, word [.cluster]
 sub ax, 0x2
-mul byte [.clustersize]
-add ax, [.datastart]
+mul byte [clustersize]
+add ax, [datastart]
 ;Set the destination
 mov bx, word [.pointer]
 ;Set the size
 mov ch, 0x0
-mov cl, byte [.clustersize]
+mov cl, byte [clustersize]
 ;Store the loop counter in the stack
 .loadsector:
 push cx
@ -303,7 +303,7 @@ int 0x13
 pop ax
 ;Set the next sector
 add ax, 0x1
-add bx, word [.sectorsize]
+add bx, word [sectorsize]
 ;Load the loop counter from the stack
 pop cx
 ;Load the next sector
@ -335,8 +335,8 @@ jge .success
 ;Store the address of the next cluster
 mov word [.cluster], ax
 ;Set the destination of the next cluster
-mov ax, [.sectorsize]
-mul word [.clustersize]
+mov ax, [sectorsize]
+mul word [clustersize]
 add word [.pointer], ax
 ;Load the next cluster
 jmp .loadcluster
@ -362,18 +362,6 @@ mov ah, 0x0
 iret

 ;Data
-.drive           db 0x0
-.sectorsize      dw 0x0 ;bytes
-.clustersize     db 0x0 ;sectors
-.reservedsectors dw 0x0
-.fats            db 0x0
-.rootentries     dw 0x0
-.sectorsperfat   dw 0x0
-.sectorspertrack dw 0x0
-.heads           dw 0x0
-.rootstart       dw 0x0
-.rootsectors     dw 0x0
-.datastart       dw 0x0
 .file            times 0xb db 0x20
 .size            dw 0x0
 .cluster         dw 0x0
@ -454,21 +442,21 @@ push bx
 mov bx, ax
 ;Calculate the sector
 mov dx, 0x0
-div word [.sectorspertrack]
+div word [sectorspertrack]
 add dl, 0x1
 mov cl, dl
 ;Load the logical sector from BX
 mov ax, bx
 ;Calculate the head and cylinder
 mov dx, 0x0
-div word [.sectorspertrack]
+div word [sectorspertrack]
 mov dx, 0x0
-div word [.heads]
+div word [heads]
 mov dh, dl ;Head
 mov ch, al ;Cylinder

 ;Load the drive number
-mov dl, byte [.drive]
+mov dl, byte [drive]

 ;Load BX and AX from the stack
 pop bx
--- a/src/PRINT.ASM
+++ b/src/PRINT.ASM
@ -40,7 +40,7 @@ stosb
 ;Load
 load:
 mov bx, stack + 0x100
-mov ah, 0x0
+mov ah, 0x2
 int 0x22
 ;Check for errors
 cmp al, 0x0
--- a/src/SYSTEM.ASM
+++ b/src/SYSTEM.ASM
@ -21,7 +21,7 @@ je readln
 iret
 ;Disk operations
 int0x22:
-cmp ah, 0x0
+cmp ah, 0x2
 je loadf
 ;To do: savef
 iret
@ -50,9 +50,10 @@ mov [0x82], ax
 mov [0x86], ax
 mov [0x8a], ax

-;Store the boot drive number and set the drive letter
-mov [drive], dl
-call setdriveletter
+;Store the boot drive number as the current drive and set the current
+;drive letter
+mov [curdrive], dl
+call setcurdriveletter

 ;Print a welcome message
 mov si, welcomemsg
@ -67,8 +68,8 @@ mov sp, 0x0
 sti

 ;Prompt for and read a command
-;Print the drive letter
-mov si, driveletter
+;Print the current drive letter
+mov si, curdriveletter
 mov ah, 0x0
 int 0x21
 ;Print a prompt
@ -85,26 +86,24 @@ int 0x21
 cmp byte [input], 0x0
 jz shell

-;Check for a drive change command
+;Set SI at the command
 ;Set SI at input
 mov si, input
 ;Ignore leading spaces
 call ignoreleading
-;Check
+
+;Check for a current drive change command
 cmp byte [si + 0x1], ":"
 jne extract
 cmp byte [si + 0x2], 0x0
-je changedrive
+je changecurdrive
 cmp byte [si + 0x2], 0x20
-je changedrive
+je changecurdrive

 ;Extract the specification of the program file
 extract:
-;Set SI at input and DI at program
-mov si, input
+;Set DI at program
 mov di, program
-;Ignore leading spaces
-call ignoreleading
 ;Initialise program with spaces
 mov cx, 0xe
 mov al, 0x20
@ -142,21 +141,28 @@ rep movsb
 ;Load the program
 mov bx, 0x3000
 mov si, program
-mov ah, 0x0
+mov ah, 0x2
 int 0x22
 ;Check for errors
 cmp al, 0x0
 jne shell
-;Pass the drive and command tail to the program
-mov dl, [drive]
+;Pass the current drive and command tail to the program
+mov dl, [curdrive]
 pop si
 call ignoreleading
 ;Execute the program
 jmp 0x3000

-;Change the drive
+;Print a command error message and return to the shell
+cmderror:
+mov si, cmderrormsg
+mov ah, 0x2
+int 0x21
+jmp shell
+
+;Change the current drive
 ;Get the BIOS equipment list
-changedrive:
+changecurdrive:
 int 0x11
 ;Get the number of floppy drives
 times 0x6 shr ax, 0x1
@ -184,33 +190,44 @@ int 0x21
 jmp shell
 ;Change the drive
 contchdrive:
-mov [drive], dl
-call setdriveletter
+mov [curdrive], dl
+call setcurdriveletter
 jmp shell

-;Print a command error message and return to the shell
-cmderror:
-mov si, cmderrormsg
-mov ah, 0x2
-int 0x21
-jmp shell
+;Welcome message
+welcomemsg db 0xd, 0xa, "Welcome to EttinOS!", 0xd, 0xa, 0x0

-;Data
-welcomemsg   db 0xd, 0xa, "Welcome to EttinOS!", 0xd, 0xa, 0x0
-drive        db 0x0
-driveletter  db "?:", 0x0
+;Drive stuff
+curdrive     db 0x0
 driveletters db "AaBbCcDd"
-prompt       db "> ", 0x0
-input        times 0x4c db 0x0
-program      times 0xf db 0x0
-extension    db ".BIN", 0x0
-cmderrormsg  db "File or command not found", 0x0
-driverrormsg db "Drive not found", 0x0
+
+;Shell
+curdriveletter db "?:", 0x0
+prompt         db "> ", 0x0
+input          times 0x4c db 0x0
+program        times 0xf db 0x0
+extension      db ".BIN", 0x0
+cmderrormsg    db "File or command not found", 0x0
+driverrormsg   db "Drive not found", 0x0
+
+;Disk parameters
+drive           db 0x0
+sectorsize      dw 0x0 ;bytes
+clustersize     db 0x0 ;sectors
+reservedsectors dw 0x0
+fats            db 0x0
+rootentries     dw 0x0
+sectorsperfat   dw 0x0
+sectorspertrack dw 0x0
+heads           dw 0x0
+rootstart       dw 0x0
+rootsectors     dw 0x0
+datastart       dw 0x0

 ;***

 ;Set the drive letter
-setdriveletter:
+setcurdriveletter:

 ;Set the drive number and letter counters
 mov dh, 0x0
@ -227,7 +244,7 @@ jmp .checkdrive
 ;Set the drive letter
 .set:
 mov al, [si]
-mov byte [driveletter], al
+mov byte [curdriveletter], al

 ;Return
 ret