52 lines
1.9 KiB
Plaintext
52 lines
1.9 KiB
Plaintext
;;********************************************************************************
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;; @module ps2_keyboard
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;; @type driver
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;; @details:
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;; Support for a PS2 Keyboard using the shift register of a 6522 VIA
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;; @section Reading a scancode/command answer
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;; Pressing a key causes 11 bits to be sent: 1 start - 8 scancode - 1 parity - 1 stop
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;; The VIA is set up to interrupt after 8 bits have been shifted into the shift register
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;; from the external clock pulses of the keyboard (additional hardware required to
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;; address the hardware bug of the VIA, where bit get lost when the external clock
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;; transition happens during falling edge of PHI2). After reading the shift register,
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;; the VIAs T2 timer is set to interrupt after the last 3 bits have been shifted in,
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;; which takes about ~230ms.
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;; T2 is used because it leaves to more versatile T1 available for something else
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;; @section Processing a scancode
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;; The scancode may be processed by storing the address of a handler subroutine in
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;; ps2kb::scancode_handler. This handler can load the scancode byte from ps2kb::scancode.
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;;
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;;
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;; To use a different layout, change the enum K and the CHARS_NOMOD and CHARS_MODSHIFT
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;; @warning
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;; The value with which the timer is loaded must depends on the clock frequency
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;; of the keyboard and the computer
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;;
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;;********************************************************************************
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.ifndef INCLUDE_PS2_KEYBOARD
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INCLUDE_PS2_KEYBOARD = 1
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.include "system.h65"
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.scope ps2kb
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Import ps2kb,init,begin_receive,send_command,scancode,status,scancode_handler
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Import ps2kb, _receive_irq_shift_reg_handler, _receive_irq_timer_handler
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VIA = IO1
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TIMER = 230 ; 230 ms (@1MHz)
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; use RA4 to pull the clock low
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CLK_PULL_MASK= %00001000
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CLK_PULL_R = IO::RANH
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CLK_PULL_DDR = IO::DDRA
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.enum STATUS
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RECEIVE_KEYS = %10000000
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RECEIVE_ANSWER = %01000000
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SEND_CMD = %00100000
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NONE = %00000000
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.endenum
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.endscope
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.endif ; guard
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