The Keyboard ControllerOur near-term goalKeyboard and its controllerKB Controller StatusA few Controller CommandsInterrupt-Handler actionsKeyboard QueueBIOS DATA AREAFormat of KBFLAGS LSBDemo ‘minikybd.s’The Keyboard ControllerEssential steps for implementing an interrupt service routine for the Keyboard ControllerOur near-term goal•To build a ‘mini’ x86 operating system •It should be able run a Linux application •It needs to support:–basic console input/output (keyboard, screen)–handling of device-interrupts (timer, keyboard)–‘exit’ gracefully when application is finished–utilize x86 privilege restrictions and 32bit code•Most needed building-blocks already doneKeyboard and its controllerKeyboard ControllerCPUPICbusKEYBOARDPS/2 MOUSEoutput portTIMERoutput bufferstatus regcontrol reg0x64 0x64 0x60 0x60input bufferinput portRAMPIC6KB Controller StatusPARE TIM AUXB KEYL C / D SYSF INPB OUTB7 5 4 3 2 1 0LEGEND OUTB: Output-Buffer Full (1=yes, 0=no) INPB: Input-Buffer Full (1=yes, 0=no) SYSF: System-Flag (1=self-test successful, 0=power-on reset) C/D: Command/Data was written to (1=port 0x64, 0=port 0x60) KEYL: Keyboard-Lock status (1=keyboard available, 0=locked) AUXB: Output-Buffer’s data is (1=for mouse, 0=for keyboard) TIM: General Timeout-Error has occurred (1=yes, 0=no) PARE: Parity-Error on last byte from keyboard/mouse (1=yes, 0=no)A few Controller Commands•0xAD: Disable Keyboard•0xAE: Enable Keyboard•0xA7: Disable PS/2 Mouse•0xA8: Enable PS/2 Mouse•0xC0: Read input-port (to output buffer)•0XD0: Read output-port (to output buffer)Interrupt-Handler actions•When the keyboard-controller issues an interrupt, these actions should be taken:–Save values in the working CPU registers–Read keyboard-controller’s status-register–If the output-buffer has new data, read it–If a “special” key (shift/toggle), adjust kb_flags–For a normal key, translate scancode to ascii–Insert the code-pair at tail-end of kb-queue–Send EOI-command to Interrupt Controller–Restore the saved values from CPU registers–Resume the interrupted procedure (with ‘iret’)Keyboard QueueKBHEADKBTAILBIOS DATA AREA•KBFLAGS is word at address 0x40:0x17•KBHEAD is word at address 0x40:0x1A•KBTAIL is word at address 0x40:0x1C•KBQUEUE is array of 16 words array base-address at 0x40:0x1E•KBBASE is word at 0x40:0x80•KBTAIL is word at 0x40:0x82Format of KBFLAGS LSB Left-Shift key is pressed (1=yes, 0=no)Right-Shift key is pressed (1=yes, 0=no)01Ctrl-Key is pressed (1=yes, 0=no)Alt-Key is pressed (1=yes, 0=no)234567Caps-Lock is active (1=yes, 0=no)Num-Lock is active (1=yes, 0=no)Scroll-Lock is active (1=yes, 0=no)Insert-mode is active (1=yes, 0=no)Demo ‘minikybd.s’•It shows a minimal implementation for the keyboard-controller’s interrupt-handler•It runs in Real-Mode•It ‘echos’ a user’s keystrokesIN-CLASS EXERCISE: modify this demo to run in
View Full Document
Unlocking...