org 0xF000 DEF_KBOfRAM: equ 0x30 DEF_SysFeatures: equ 0x80 dw 0xAA55 dw 0x1000 biosStart: move sp,0x0100 ; Initialize interrupt vectors xor pa,pa move a,vec_none move vt,pa move word [pa],vec_divError move word [pa+2],vec_breakpoint move word [pa+4],vec_invOpcode move word [pa+6],vec_coproErr move word [pa+8],vec_sysCall move word [pa+10],vec_invAddx move word [pa+12],vec_Fx move word [pa+14],vec_Fx move word [pa+16],vec_Fx {{ add pa,18 move cl,16-9 fillLoop: move [pa],a ldax pa,[pa+2] iter cl,fillLoop }} move word [pa],vec_irq0 move word [pa+2],vec_irq1 move word [pa+4],vec_irq2 move word [pa+6],vec_irq3 {{ add pa,8 move cl,12 fillLoop: move [pa],a ldax pa,[pa+2] iter cl,fillLoop }} ; Initialize serial interface and print startup message move pd,0xC009 move [pd],bl ; Set DTR move [pd+1],a ; Disable IRQ, clear R3 move pb,pa move pa,str_startup call printString move pa,pb ; Clear out RAM xor a,a {{ fillLoop: move [pa],a ldax pa,[pa+2] cmp pa,0xC000 jl fillLoop }} ; Initialize PIC: Enable everything xor a,a move b,1 move byte [pa],0x0F ; Initialize PIT: Clear it to 0 move [pa+2],a ; Set up the system configuration registers move byte [pa+5],DEF_KBOfRAM move byte [pa+6],DEF_SysFeatures ; Initialize FDC1 move [pa+0x12],b ; Turn motor on ; Initialize FDC2 move [pa+0x18],a ; Clear SSR1/SSR2 move [pa+0x1A],a ; Turn motor off move [pa+0x0E],a ; Disable interrupt ; Load first sector of diskette ; Recalib. move a,0x000A sysc jc bootError move a,0x000C xor b,b xor c,c move pa,0x0100 sysc jc bootError ; Jump into bootloader movx b:a,b movx d:c,a xor pa,pa xor pb,pb xor pc,pc xor pd,pd and fl,0x02 or f,0x0102 jump 0x100 ; We couldn't boot; let the user know and freeze. bootError: move pa,str_noBoot call printString and f,0x00FF halt ;------------------------------------------------------------------------------ ; printString: Prints the ASCIZ string whose first character is [pa]. printString: push a push b move a,0x0007 {{ loop: move bl,[pa] cmp bl,0 je done sysc ldax pa,[pa+1] jump loop done: }} pop b pop a retn ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; vec_divError: move pa,str_badVector jump dumpAndDie vec_breakpoint: move pa,str_breakpoint jump dumpAndDie vec_invOpcode: move pa,str_invOpcode jump dumpAndDie vec_coproErr: move pa,str_coproErr jump dumpAndDie vec_invAddx: move pa,str_invAddx jump dumpAndDie vec_Fx: move pa,str_Fx jump dumpAndDie ; IRQ0: Timer interrupt vec_irq0: push pd move pd,0xC002 move word [pd],0x0000 ; ACK the IRQ jump irq_iret ; IRQ1: Serial interface interrupt vec_irq1: push pd move pd,0xC00A move byte [pd],0x0000 ; ACK/disable the IRQ jump irq_iret ; IRQ2: Primary FDC interrupt vec_irq2: push pd move pd,0xC016 move byte [pd],0x00 ; ACK/disable the IRQ jump irq_iret ; IRQ3: Secondary FDC interrupt vec_irq3: push pd move pd,0xC01E move byte [pd],0x00 ; ACK/disable the IRQ irq_iret: pop d pop f retn vec_none: move pa,str_badVector dumpAndDie: call printString move pa,str_rebooting call printString reset_system: move pa,0xC007 move byte [pa],1 and f,0x00FF halt vec_sysCall: {{ push d push pd cmp al,0x0E jg invalidSysCall movx d,al move pd,jumpTable ldax pd,[pd+d*2] jump [pd] jumpTable: dw reset_system,func01,func02,func03 dw func04,func05,func06,func07 dw func08,func09,func0A,func0B dw func0C,func0D,func0E invalidSysCall: or byte [sp+4],4 ; Set FL.CF for return iret: pop pd pop d pop f retn ; Set interrupt vector ; In: AL = 0x01 ; AH = vector number ; PA = handler address ; Out: PA = old handler address func01: push pc move pd,vt movx d,ah and d,0x1F move pc,[pd+d*2] move [pd+d*2],pa move pa,pc pop pc jump iret ; Get interrupt vector ; In: AL = 0x02 ; AH = vector number ; Out: PA = handler address func02: move pd,vt movx d,ah and d,0x1F move pa,[pd+d*2] jump iret ; Set timeout for PIT ; In: AL = 0x03 ; B = count func03: move pd,0xC002 move [pd],b jump iret ; Get memory size ; In: AL = 0x04 ; Out: A = KB of system RAM func04: move a,DEF_KBOfRAM jump iret ; Get system features ; In: AL = 0x05 ; Out: AL = system feature bits func05: move al,DEF_SysFeatures jump iret ; Get serial port status ; In: AL = 0x06 ; AH = serial port number ; Out: AL = port status bits func06: cmp ah,0 {{ jne noPort move pd,0xC008+1 move dl,[pd] move dh,dl move al,dl and al,2 and dl,4 and dh,8 shl dl,1 shr dh,1 or al,1 or al,dl or al,dh jump iret noPort: xor al,al jump iret }} ; Write to serial port ; In: AL = 0x07 ; AH = serial port number ; BL = byte to send ; Out: FL.CF set if there was an error func07: cmp ah,0 jne noSerialPort {{ move pd,0xC008 ; Set DTROUT move byte [pd+1],1 test byte [pd+1],2 ; If DTRIN is low, jz noTerminal ; there's no terminal ; Wait for CTSIN & clear line, and make sure DTRIN ; stays high move dh,0 waitReady: move dl,[pd+1] test dl,2 jz noTerminal and dl,0x1A cmp dl,0x1A je ready iter dh,waitReady jump serialTimeout ready: move [pd],bl and byte [sp+4],~4 jump iret }} ; Read from serial port ; In: AL = 0x08 ; AH = serial port number ; Out: FL.CF set on error; else AL = byte read func08: cmp ah,0 jne noSerialPort {{ move pd,0xC008 ; Set DTROUT move byte [pd+1],1 test byte [pd+1],2 ; If DTRIN is low, jz noTerminal ; there's no terminal ; Wait for a byte to be ready and make sure DTRIN stays ; high. move dh,0 waitReady: move dl,[pd+1] test dl,2 jz noTerminal and dl,0x06 cmp dl,0x06 je ready iter dh,waitReady jump serialTimeout ready: move al,[pd] and byte [sp+4],~4 jump iret }} noDrive: noSerialPort: move al,0x01 jump invalidSysCall noMedium: noTerminal: move al,0x02 jump invalidSysCall seekError: serialTimeout: move al,0x03 jump invalidSysCall driveError: move al,0x04 jump invalidSysCall FDC_SSR1: equ 0 FDC_SSR2: equ 1 FDC_DSR: equ 2 FDC_MSR: equ 3 FDC_CMD: equ 4 FDC_DATA: equ 5 FDC_ICR: equ 6 ; Get floppy drive status ; In: AL = 0x09 ; AH = Drive number ; Out: AL = status byte func09: {{ cmp ah,1 jg ret0 call getDriveAddx jz ret0 move d,[pd+FDC_DSR] and dl,0x06 move al,dl or al,0x01 test dh,0x01 jz notBusy or al,0x08 notBusy: jump iret ret0: move al,0 jump iret }} ; Recalibrate floppy drive ; In: AL = 0x0A ; AH = Drive number ; Out: FL.CF set if there was an error func0A: cmp ah,1 jg noDrive call getDriveAddx jz noDrive move byte [pd+FDC_DSR],1 move d,[pd+FDC_DSR] test dl,0x02 jz noMedium xor d,d move word [pd+FDC_SSR1],d move word [pd+FDC_ICR],d move byte [pd+FDC_CMD],dl {{ waitReady: test byte [pd+FDC_MSR],0x01 jnz waitReady }} jump diskReturn ; Seek drive head ; In: AL = 0x0B ; AH = Drive number ; BL = Track ; Out: FL.CF set if error func0B: cmp ah,1 jg noDrive call getDriveAddx jz noDrive move byte [pd+FDC_DSR],1 move d,[pd+FDC_DSR] test dl,0x02 jz noMedium cmp bl,39 jg badParams xor d,d move [pd+FDC_SSR1],bl move byte [pd+FDC_SSR2],dl move word [pd+FDC_ICR],d move byte [pd+FDC_CMD],0x30 {{ waitReady: test byte [pd+FDC_MSR],0x01 jnz waitReady }} jump diskReturn ; Read sector from floppy drive ; In: AL = 0x0C ; AH = Drive number ; BL = Track ; BH = Sector ; CL = Head ; PA = Out buffer base ; Out: FL.CF set if error func0C: cmp ah,1 jg noDrive_2 call getDriveAddx jz noDrive_2 {{ move byte [pd+FDC_DSR],1 move d,[pd+FDC_DSR] test dl,0x02 jz noMedium_2 call checkParams move [pd+FDC_SSR1],bl move dl,bh test cl,cl jz head0 or dl,0x80 head0: move byte [pd+FDC_SSR2],dl xor d,d move word [pd+FDC_ICR],d move byte [pd+FDC_CMD],0x10 waitReady: test byte [pd+FDC_MSR],0x01 jnz waitReady cmp byte [pd+FDC_MSR],0 jnz diskReturn ; Buffer in 512 bytes push a move a,0x100 readLoop: move dl,[pd+FDC_DATA] move dh,[pd+FDC_DATA] move [pa],d ldax pa,[pa+2] iter a,readLoop sub pa,512 pop a }} and byte [sp+4],~4 jump iret noDrive_2: jump noDrive noMedium_2: jump noMedium seekError_2: jump seekError driveError_2: jump driveError ; Write sector to floppy drive ; In: AL = 0x0D ; AH = Drive number ; BL = Track ; BH = Sector ; CL = Head ; PA = Input buffer base ; Out: FL.CF set if error func0D: cmp ah,1 jg noDrive_2 call getDriveAddx jz noDrive_2 {{ move byte [pd+FDC_DSR],1 move d,[pd+FDC_DSR] test dl,0x02 jz noMedium_2 call checkParams move [pd+FDC_SSR1],bl move dl,bh test cl,cl jz head0 or dl,0x80 head0: move byte [pd+FDC_SSR2],dl xor d,d move word [pd+FDC_ICR],d move byte [pd+FDC_CMD],0x20 waitReady: test byte [pd+FDC_MSR],0x01 jnz waitReady cmp byte [pd+FDC_MSR],0 jnz diskReturn ; Buffer out 512 bytes push a move a,0x100 writeLoop: move d,[pa] move [pd+FDC_DATA],dl move [pd+FDC_DATA],dh ldax pa,[pa+2] iter a,writeLoop sub pa,512 pop a }} and byte [sp+4],~4 jump iret ; Format track of floppy drive ; In: AL = 0x0D ; AH = drive number ; BL = track number ; Out: FL.CF set if error func0E: cmp ah,1 jg noDrive_2 call getDriveAddx jz noDrive_2 move byte [pd+FDC_DSR],1 move d,[pd+FDC_DSR] test dl,0x02 jz noMedium_2 cmp bl,39 jg badParams xor d,d move [pd+FDC_SSR1],bl move byte [pd+FDC_SSR2],dl move word [pd+FDC_ICR],d move byte [pd+FDC_CMD],0x30 {{ waitReady: test byte [pd+FDC_MSR],0x01 jnz waitReady }} ; Handle return stuff diskReturn: {{ move byte [pd+FDC_DSR],0 test byte [pd+FDC_MSR],0x9E jz success test byte [pd+FDC_MSR],0x0E jnz skipSeekError jump seekError skipSeekError: test byte [pd+FDC_MSR],0x80 jz driveErrorJump test byte [pd+FDC_DSR],0x02 jnz skipNM driveErrorJump: jump driveError skipNM: jump noMedium success: and byte [sp+4],~4 jump iret }} ; Set PD to the base address of the drive's device I/O space getDriveAddx: move pd,0xC010 {{ test ah,ah jz drive0 ldax pd,[pd+8] drive0: test byte [pd+FDC_DSR],0x80 retn }} ; Check drive parameters checkParams: cmp bl,39 jg badParams cmp bh,8 jg badParams cmp cl,1 jg badParams retn badParams: move al,0 jump invalidSysCall }};syscall NUL: equ 0 BEL: equ 7 LF: equ 10 FF: equ 12 CR: equ 13 str_startup: db BEL,FF,"Viejo 20 BIOS",CR,LF db " Version 1.0",CR,LF,NUL str_divErr: db BEL,"Divide error",NUL str_breakpoint: db BEL,"Unhandled breakpoint",NUL str_invOpcode: db BEL,"Invalid opcode",NUL str_coproErr: db BEL,"Coprocessor error",NUL str_invAddx: db BEL,"Invalid address generated",NUL str_Fx: db BEL,"Unhandled emulation trap",NUL str_badVector: db BEL,"Invalid vector called",NUL str_rebooting: db CR,LF,"Resetting system...",CR,LF,NUL str_noBoot: db BEL,"*** Unable to load from primary " db "floppy disk ***",CR,LF db "System halted",CR,LF,NUL org 0xFFF0 systemReset: jump biosStart