Linux asm - int 16h analogue to read raw keyboard scancodes
For my studies I need to write a program on asm, which will wait until the keyboard key is pressed, and then print it's scan-code and ASCII code of the key's character.
I know that BIOS's int 16h can do the job, but I am using Linux right now and can't find an appropriate analogue syscall for it.
What should I use for this task? I am currently using Debian Stretch and NASM for my assembly code.
linux assembly keyboard nasm scancodes
asked Nov 23 '18 at 20:20
VerlorenVerloren
508
add a comment |
For my studies I need to write a program on asm, which will wait until the keyboard key is pressed, and then print it's scan-code and ASCII code of the key's character.
I know that BIOS's int 16h can do the job, but I am using Linux right now and can't find an appropriate analogue syscall for it.
What should I use for this task? I am currently using Debian Stretch and NASM for my assembly code.
linux assembly keyboard nasm scancodes
asked Nov 23 '18 at 20:20
VerlorenVerloren
508
This is not easily possible due to the keyboard being several layers of abstraction away from your program. For a console application, the easiest way is to first set the terminal into unbuffered mode and then to read a single character. This is a bit annoying to do but feasible from assembly.
– fuz
Nov 23 '18 at 20:32
Another approach, which might lead to simpler code but more complex preparations to execute, would be to write a real-mode program that just usesint 16h(and other appropriate BIOS features), compile it to a self-contained binary, and install that where the PC's bootloader (often GRUB) can find and execute it. For testing, you could run a virtual PC and use the virtual bootloader to run your binary.
– Dave M.
Nov 23 '18 at 20:33
You might be able to use the "input" subsystem for this. See man input-events.
– Jester
Nov 23 '18 at 22:32
add a comment |
For my studies I need to write a program on asm, which will wait until the keyboard key is pressed, and then print it's scan-code and ASCII code of the key's character.
I know that BIOS's int 16h can do the job, but I am using Linux right now and can't find an appropriate analogue syscall for it.
What should I use for this task? I am currently using Debian Stretch and NASM for my assembly code.
linux assembly keyboard nasm scancodes
asked Nov 23 '18 at 20:20
VerlorenVerloren
508
For my studies I need to write a program on asm, which will wait until the keyboard key is pressed, and then print it's scan-code and ASCII code of the key's character.
I know that BIOS's int 16h can do the job, but I am using Linux right now and can't find an appropriate analogue syscall for it.
What should I use for this task? I am currently using Debian Stretch and NASM for my assembly code.
linux assembly keyboard nasm scancodes
linux assembly keyboard nasm scancodes
asked Nov 23 '18 at 20:20
VerlorenVerloren
508
asked Nov 23 '18 at 20:20
VerlorenVerloren
508
edited Nov 24 '18 at 10:26
Verloren
asked Nov 23 '18 at 20:20
VerlorenVerloren
508
asked Nov 23 '18 at 20:20
VerlorenVerloren
508
asked Nov 23 '18 at 20:20
VerlorenVerloren
508
508
This is not easily possible due to the keyboard being several layers of abstraction away from your program. For a console application, the easiest way is to first set the terminal into unbuffered mode and then to read a single character. This is a bit annoying to do but feasible from assembly.
– fuz
Nov 23 '18 at 20:32
Another approach, which might lead to simpler code but more complex preparations to execute, would be to write a real-mode program that just usesint 16h(and other appropriate BIOS features), compile it to a self-contained binary, and install that where the PC's bootloader (often GRUB) can find and execute it. For testing, you could run a virtual PC and use the virtual bootloader to run your binary.
– Dave M.
Nov 23 '18 at 20:33
You might be able to use the "input" subsystem for this. See man input-events.
– Jester
Nov 23 '18 at 22:32
add a comment |
This is not easily possible due to the keyboard being several layers of abstraction away from your program. For a console application, the easiest way is to first set the terminal into unbuffered mode and then to read a single character. This is a bit annoying to do but feasible from assembly.
– fuz
Nov 23 '18 at 20:32
Another approach, which might lead to simpler code but more complex preparations to execute, would be to write a real-mode program that just usesint 16h(and other appropriate BIOS features), compile it to a self-contained binary, and install that where the PC's bootloader (often GRUB) can find and execute it. For testing, you could run a virtual PC and use the virtual bootloader to run your binary.
– Dave M.
Nov 23 '18 at 20:33
You might be able to use the "input" subsystem for this. See man input-events.
– Jester
Nov 23 '18 at 22:32
This is not easily possible due to the keyboard being several layers of abstraction away from your program. For a console application, the easiest way is to first set the terminal into unbuffered mode and then to read a single character. This is a bit annoying to do but feasible from assembly.
– fuz
Nov 23 '18 at 20:32
This is not easily possible due to the keyboard being several layers of abstraction away from your program. For a console application, the easiest way is to first set the terminal into unbuffered mode and then to read a single character. This is a bit annoying to do but feasible from assembly.
– fuz
Nov 23 '18 at 20:32
Another approach, which might lead to simpler code but more complex preparations to execute, would be to write a real-mode program that just uses
int 16h (and other appropriate BIOS features), compile it to a self-contained binary, and install that where the PC's bootloader (often GRUB) can find and execute it. For testing, you could run a virtual PC and use the virtual bootloader to run your binary.– Dave M.
Nov 23 '18 at 20:33
Another approach, which might lead to simpler code but more complex preparations to execute, would be to write a real-mode program that just uses
int 16h (and other appropriate BIOS features), compile it to a self-contained binary, and install that where the PC's bootloader (often GRUB) can find and execute it. For testing, you could run a virtual PC and use the virtual bootloader to run your binary.– Dave M.
Nov 23 '18 at 20:33
You might be able to use the "input" subsystem for this. See man input-events.
– Jester
Nov 23 '18 at 22:32
You might be able to use the "input" subsystem for this. See man input-events.
– Jester
Nov 23 '18 at 22:32
add a comment |
1 Answer
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Normally the kernel translates keyboard scancodes into ASCII characters that you can read on a tty. But there are ways to get raw scancodes, e.g. look at how showkey(1) does it (http://kbd-project.org/) on a text console. https://wiki.archlinux.org/index.php/Keyboard_input
https://github.com/legionus/kbd/blob/2.0.4/src/showkey.c shows that you can use an ioctl(2) on a file descriptor for the console terminal to set the KBD translation mode to RAW (scancodes) or MEDIUMRAW (keycodes). Then you can make normal read system calls.
ioctl(fd, KDSKBMODE, show_keycodes ? K_MEDIUMRAW : K_RAW)
Obviously you can make these system calls from hand-written asm using syscall on x86-64 or int 0x80 on 32-bit x86, looking up the syscall numbers in asm/unistd_64.h, and the values of other constants in their respective headers.
showkey takes care to set up a watchdog timer to exit cleanly, and catch signals, because doing this intercepts keys before the kernel processes control-C or ctrl+alt+f2 sequences. So without a timeout, there'd be no way to exit the program. And if you exited without restoring normal mode, there'd be no way to type on the console to run a command to restore normal keyboard mode.
answered Nov 23 '18 at 20:35
Peter CordesPeter Cordes
127k18190326
Note that this only works in the virtual console, not inside a terminal emulator.
– fuz
Nov 23 '18 at 20:39
add a comment |
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Normally the kernel translates keyboard scancodes into ASCII characters that you can read on a tty. But there are ways to get raw scancodes, e.g. look at how showkey(1) does it (http://kbd-project.org/) on a text console. https://wiki.archlinux.org/index.php/Keyboard_input
https://github.com/legionus/kbd/blob/2.0.4/src/showkey.c shows that you can use an ioctl(2) on a file descriptor for the console terminal to set the KBD translation mode to RAW (scancodes) or MEDIUMRAW (keycodes). Then you can make normal read system calls.
ioctl(fd, KDSKBMODE, show_keycodes ? K_MEDIUMRAW : K_RAW)
Obviously you can make these system calls from hand-written asm using syscall on x86-64 or int 0x80 on 32-bit x86, looking up the syscall numbers in asm/unistd_64.h, and the values of other constants in their respective headers.
showkey takes care to set up a watchdog timer to exit cleanly, and catch signals, because doing this intercepts keys before the kernel processes control-C or ctrl+alt+f2 sequences. So without a timeout, there'd be no way to exit the program. And if you exited without restoring normal mode, there'd be no way to type on the console to run a command to restore normal keyboard mode.
answered Nov 23 '18 at 20:35
Peter CordesPeter Cordes
127k18190326
Note that this only works in the virtual console, not inside a terminal emulator.
– fuz
Nov 23 '18 at 20:39
add a comment |
Normally the kernel translates keyboard scancodes into ASCII characters that you can read on a tty. But there are ways to get raw scancodes, e.g. look at how showkey(1) does it (http://kbd-project.org/) on a text console. https://wiki.archlinux.org/index.php/Keyboard_input
https://github.com/legionus/kbd/blob/2.0.4/src/showkey.c shows that you can use an ioctl(2) on a file descriptor for the console terminal to set the KBD translation mode to RAW (scancodes) or MEDIUMRAW (keycodes). Then you can make normal read system calls.
ioctl(fd, KDSKBMODE, show_keycodes ? K_MEDIUMRAW : K_RAW)
Obviously you can make these system calls from hand-written asm using syscall on x86-64 or int 0x80 on 32-bit x86, looking up the syscall numbers in asm/unistd_64.h, and the values of other constants in their respective headers.
showkey takes care to set up a watchdog timer to exit cleanly, and catch signals, because doing this intercepts keys before the kernel processes control-C or ctrl+alt+f2 sequences. So without a timeout, there'd be no way to exit the program. And if you exited without restoring normal mode, there'd be no way to type on the console to run a command to restore normal keyboard mode.
answered Nov 23 '18 at 20:35
Peter CordesPeter Cordes
127k18190326
Note that this only works in the virtual console, not inside a terminal emulator.
– fuz
Nov 23 '18 at 20:39
add a comment |
Normally the kernel translates keyboard scancodes into ASCII characters that you can read on a tty. But there are ways to get raw scancodes, e.g. look at how showkey(1) does it (http://kbd-project.org/) on a text console. https://wiki.archlinux.org/index.php/Keyboard_input
https://github.com/legionus/kbd/blob/2.0.4/src/showkey.c shows that you can use an ioctl(2) on a file descriptor for the console terminal to set the KBD translation mode to RAW (scancodes) or MEDIUMRAW (keycodes). Then you can make normal read system calls.
ioctl(fd, KDSKBMODE, show_keycodes ? K_MEDIUMRAW : K_RAW)
Obviously you can make these system calls from hand-written asm using syscall on x86-64 or int 0x80 on 32-bit x86, looking up the syscall numbers in asm/unistd_64.h, and the values of other constants in their respective headers.
showkey takes care to set up a watchdog timer to exit cleanly, and catch signals, because doing this intercepts keys before the kernel processes control-C or ctrl+alt+f2 sequences. So without a timeout, there'd be no way to exit the program. And if you exited without restoring normal mode, there'd be no way to type on the console to run a command to restore normal keyboard mode.
answered Nov 23 '18 at 20:35
Peter CordesPeter Cordes
127k18190326
Normally the kernel translates keyboard scancodes into ASCII characters that you can read on a tty. But there are ways to get raw scancodes, e.g. look at how showkey(1) does it (http://kbd-project.org/) on a text console. https://wiki.archlinux.org/index.php/Keyboard_input
https://github.com/legionus/kbd/blob/2.0.4/src/showkey.c shows that you can use an ioctl(2) on a file descriptor for the console terminal to set the KBD translation mode to RAW (scancodes) or MEDIUMRAW (keycodes). Then you can make normal read system calls.
ioctl(fd, KDSKBMODE, show_keycodes ? K_MEDIUMRAW : K_RAW)
Obviously you can make these system calls from hand-written asm using syscall on x86-64 or int 0x80 on 32-bit x86, looking up the syscall numbers in asm/unistd_64.h, and the values of other constants in their respective headers.
showkey takes care to set up a watchdog timer to exit cleanly, and catch signals, because doing this intercepts keys before the kernel processes control-C or ctrl+alt+f2 sequences. So without a timeout, there'd be no way to exit the program. And if you exited without restoring normal mode, there'd be no way to type on the console to run a command to restore normal keyboard mode.
answered Nov 23 '18 at 20:35
Peter CordesPeter Cordes
127k18190326
answered Nov 23 '18 at 20:35
Peter CordesPeter Cordes
127k18190326
answered Nov 23 '18 at 20:35
Peter CordesPeter Cordes
127k18190326
answered Nov 23 '18 at 20:35
Peter CordesPeter Cordes
127k18190326
127k18190326
Note that this only works in the virtual console, not inside a terminal emulator.
– fuz
Nov 23 '18 at 20:39
add a comment |
Note that this only works in the virtual console, not inside a terminal emulator.
– fuz
Nov 23 '18 at 20:39
Note that this only works in the virtual console, not inside a terminal emulator.
– fuz
Nov 23 '18 at 20:39
Note that this only works in the virtual console, not inside a terminal emulator.
– fuz
Nov 23 '18 at 20:39
add a comment |
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This is not easily possible due to the keyboard being several layers of abstraction away from your program. For a console application, the easiest way is to first set the terminal into unbuffered mode and then to read a single character. This is a bit annoying to do but feasible from assembly.
– fuz
Nov 23 '18 at 20:32
Another approach, which might lead to simpler code but more complex preparations to execute, would be to write a real-mode program that just uses
int 16h(and other appropriate BIOS features), compile it to a self-contained binary, and install that where the PC's bootloader (often GRUB) can find and execute it. For testing, you could run a virtual PC and use the virtual bootloader to run your binary.– Dave M.
Nov 23 '18 at 20:33
You might be able to use the "input" subsystem for this. See man input-events.
– Jester
Nov 23 '18 at 22:32