135 lines
4.8 KiB
Text
135 lines
4.8 KiB
Text
## ============================= Memory Mapped Devices and Registers =============================
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@group MemoryAddresses
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MBR 0x1380
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INT_VEC 0x1080
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DISK_INTERFACE 0x1580
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RAM 0x1740
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CMOS 0x1000
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@end
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@group CMOS_Settings
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BOOT_DISK {MemoryAddresses.CMOS + 0x0010}
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@end
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## ===============================================================================================
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.load 0x0000 ## BIOS is mapped to address 0x0000 in memory
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.data
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$bios_version_number 0x00, 0x01 ## BIOS Version stored in memory
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## ============================= BIOS Program =============================
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.code
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## mov FL, 0
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## jmp 0x1740
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mov FL, 0b0000000000000001 ## Zero the FL Register and enable interrupts
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movb [{MemoryAddresses.INT_VEC + (0x20 * 3)}], 0xFF ## Setting up int 0x20 handler
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mov [{MemoryAddresses.INT_VEC + (0x20 * 3) + 1}], $_int_20_handler ## --
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mov R10, 0x00 ## Setting up int 0x30 handler by using int 0x20 functionality
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mov R9, $_int_30_handler ## -Passing the handler's address
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mov R8, 0x30 ## -Passing the interrupt's code to setup
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int 0x20 ## -Calling int 0x20 with 0x00 as parameter, to set new handler up
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## MBR Loading
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and FL, 0b1111111111111110 ## Disable interrupts
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push 0
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call $_load_mbr_data_block
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or FL, 0b0000000000000001 ## Enable interrupts
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## ----
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jmp MemoryAddresses.MBR ## Jump to start of MBR in memory
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hlt ## Just in case somehow execution reaches this point
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## ========================================================================
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## ============================= BIOS Interrupt handler =============================
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_int_20_handler:
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mov ACC, R10
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jeq $_int_20_disk_interface, 0x0010
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jeq $_int_20_set_new_interrupt_handler, 0x0000
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jeq $_int_20_clear_interrupt, 0x0001
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jmp $_int_20_end
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_int_20_disk_interface:
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movb [{MemoryAddresses.DISK_INTERFACE + 0x1}], *R9 ## Mode
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inc R9
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movb [{MemoryAddresses.DISK_INTERFACE + 0x2}], *R9 ## Disk
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inc R9
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mov [{MemoryAddresses.DISK_INTERFACE + 0x3}], *R9 ## Sector
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inc R9
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inc R9
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mov [{MemoryAddresses.DISK_INTERFACE + 0x5}], *R9 ## Address
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inc R9
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inc R9
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mov [{MemoryAddresses.DISK_INTERFACE + 0x7}], *R9 ## Size
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inc R9
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inc R9
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mov [{MemoryAddresses.DISK_INTERFACE + 0x9}], *R9 ## Memory Address
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movb [MemoryAddresses.DISK_INTERFACE], 0x00 ## Signal set to "Start Operation"
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jmp $_int_20_end
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_int_20_set_new_interrupt_handler:
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push R8 ## Interrupt Code
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push R9 ## Handler Address
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push 2
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call $_set_interrupt_vector_entry
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jmp $_int_20_end
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_int_20_clear_interrupt:
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push R9
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push 0x0000
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push 2
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call $_set_interrupt_vector_entry
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_int_20_end:
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rti
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## ==================================================================================
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## ========================== BIOS Video Interrupt handler =========================
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_int_30_handler:
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mov ACC, R10
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jeq $_int_30_clear_screen, 0x0000
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jmp $_int_30_end
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_int_30_clear_screen:
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nop
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_int_30_end:
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rti
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## ==================================================================================
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_load_mbr_data_block:
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movb [{MemoryAddresses.DISK_INTERFACE + 0x1}], 0x00 ## Mode = Read
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movb R1, [CMOS_Settings.BOOT_DISK]
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movb [{MemoryAddresses.DISK_INTERFACE + 0x2}], R1 ## Disk = Default
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mov [{MemoryAddresses.DISK_INTERFACE + 0x3}],0x0000 ## Sector = 0x0000
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mov [{MemoryAddresses.DISK_INTERFACE + 0x5}],0x0000 ## Address = 0x0000 (Start of Disk)
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mov [{MemoryAddresses.DISK_INTERFACE + 0x7}], 512 ## Size = 512 (Size of MBR is 512 bytes)
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mov [{MemoryAddresses.DISK_INTERFACE + 0x9}], MemoryAddresses.MBR ## MemoryAddress = MBR Address in memory
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movb [MemoryAddresses.DISK_INTERFACE], 0x00 ## Signal = Start
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_load_mbr_data_block_wait_loop:
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mov ACC, [{MemoryAddresses.DISK_INTERFACE + 0xB}] ## Moving <Status> register into ACC
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jne $_load_mbr_data_block_wait_loop, 0x00 ## If <Status> register not Free, loop around and wait
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ret
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_calc_interrupt_vector_address:
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arg R1
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mul R1, 0x03 ## Multiply the interrupt code by 3 for memory alignment
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mov R1, ACC
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add R1, MemoryAddresses.INT_VEC ## Add Interrupt Vector base address to Interrupt code
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mov RV, ACC
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ret
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_set_interrupt_vector_entry:
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arg R1
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push R1
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push 1
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call $_calc_interrupt_vector_address
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mov R1, RV
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arg ACC
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jeq $_set_interrupt_vector_entry_disable, 0x0000
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movb *R1, 0xFF
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jmp $_set_interrupt_vector_entry_end
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_set_interrupt_vector_entry_disable:
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movb *R1, 0x00
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_set_interrupt_vector_entry_end:
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inc R1
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mov *R1, ACC
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ret
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.fixed 4096, 0x00 ## BIOS Needs to be 4096 Bytes exactly
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