60 lines
1.8 KiB
Plaintext
60 lines
1.8 KiB
Plaintext
# check keyboard for a key
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# return 0 on no keypress or unrecognized key
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#
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# We need to do this in machine code because Mu doesn't have global variables
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# yet (for the keyboard buffer).
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== code
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# Most keys correspond to their ASCII/Unicode values.
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# TODO: Support for international keyboards and multi-byte Unicode.
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#
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# However there are some exceptions that have no assigned place in Unicode
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# (and with good reason):
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# 0x80 = left arrow ←
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# 0x81 = down arrow ↓
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# 0x82 = up arrow ↑
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# 0x83 = right arrow →
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# These code points are not used by Unicode and their semantics are agreed to
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# be context-sensitive: https://en.wikipedia.org/wiki/C0_and_C1_control_codes#C1_controls.
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# Mu cannibalizes them in yet another non-standard way.
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read-key: # kbd: (addr keyboard) -> result/eax: byte
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# . prologue
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55/push-ebp
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89/<- %ebp 4/r32/esp
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# . save registers
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51/push-ecx
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# result = 0
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b8/copy-to-eax 0/imm32
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# ecx = keyboard
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8b/-> *(ebp+8) 1/r32/ecx
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81 7/subop/compare %ecx 0/imm32
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{
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75/jump-if-!= break/disp8
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# var buffer-byte-addr/ecx: (addr byte)
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8b/-> *Keyboard-buffer:read 1/r32/CL
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81 0/subop/add %ecx Keyboard-buffer:data/imm32
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# var next-key/eax: byte = *buffer-byte-addr
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8a/byte-> *ecx 0/r32/AL
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# if (next-key != 0) lock and remove from keyboard buffer
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3d/compare-eax-with 0/imm32
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{
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74/jump-if-= break/disp8
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fa/disable-interrupts
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c6 0/subop/copy-byte *ecx 0/imm8
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ff 0/subop/increment *Keyboard-buffer:read
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81 4/subop/and *Keyboard-buffer:read 0x0f/imm32
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fb/enable-interrupts
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}
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# return
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eb $read-key:end/disp8
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}
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# TODO: fake keyboard
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$read-key:end:
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# . restore registers
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59/pop-to-ecx
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# . epilogue
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89/<- %esp 5/r32/ebp
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5d/pop-to-ebp
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c3/return
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