7486 - primitive for reading keys
It also clears keys after reading them, allowing us to read more than 16 keys.
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# check keyboard for a key
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# return 0 on no keypress or unrecognized key
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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 read/ecx: byte = keyboard buffer's read index
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8b/-> *0x7dcc 1/r32/CL # keyboard-buffer-read
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# var next-key/eax: byte = *(keyboard buffer + ecx)
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8a/byte-> *(ecx+0x7dd0) 0/r32/AL # keyboard-buffer-data
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# if (next-key != 0) lock and remove from keyboard-buffer
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81 7/subop/compare %eax 0/imm32
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{
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74/jump-if-= break/disp8
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# TODO: add some instructions in this block to SubX if we ever want to
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# use bootstrap on baremetal programs
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fa/disable-interrupts
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c6 0/subop/copy-byte *(ecx+0x7dd0) 0/imm8
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ff 0/subop/increment *0x7dcc # keyboard-buffer-read
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81 4/subop/and *0x7dcc 0xf/imm32 # keyboard-buffer-read
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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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@ -1 +1,2 @@
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sig pixel screen: (addr screen), x: int, y: int, color: int
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sig pixel screen: (addr screen), x: int, y: int, color: int
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sig read-key kbd: (addr keyboard) -> _/eax: byte
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@ -0,0 +1,31 @@
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# Draw pixels in response to keyboard events, starting from the top-left
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# and in raster order.
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#
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# To build a disk image:
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# ./translate_mu_baremetal baremetal/ex3.mu # emits disk.img
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# To run:
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# qemu-system-i386 disk.img
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# Or:
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# bochs -f baremetal/boot.bochsrc # boot.bochsrc loads disk.img
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#
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# Expected output: a new green pixel starting from the top left corner of the
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# screen every time you press a key (letter or digit)
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fn main {
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var x/ecx: int <- copy 0
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var y/edx: int <- copy 0
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{
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var key/eax: byte <- read-key 0 # real keyboard
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compare key, 0
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loop-if-= # busy wait
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pixel 0, x, y, 0x31 # green
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x <- increment
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compare x, 0x400
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{
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break-if-<
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y <- increment
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x <- copy 0
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}
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loop
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}
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}
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