1 # check keyboard for a key
 2 # return 0 on no keypress or unrecognized key
 3 #
 4 # We need to do this in machine code because Mu doesn't have global variables
 5 # yet (for the keyboard buffer).
 6 
 7 == code
 8 
 9 read-key:  # kbd: (addr keyboard) -> result/eax: byte
10     # . prologue
11     55/push-ebp
12     89/<- %ebp 4/r32/esp
13     # . save registers
14     51/push-ecx
15     # result = 0
16     b8/copy-to-eax 0/imm32
17     # ecx = keyboard
18     8b/-> *(ebp+8) 1/r32/ecx
19     81 7/subop/compare %ecx 0/imm32
20     {
21       75/jump-if-!= break/disp8
22       # var buffer-byte-addr/ecx: (addr byte)
23       8b/-> *Keyboard-buffer:read 1/r32/CL
24       81 0/subop/add %ecx Keyboard-buffer:data/imm32
25       # var next-key/eax: byte = *buffer-byte-addr
26       8a/byte-> *ecx 0/r32/AL
27       # if (next-key != 0) lock and remove from keyboard buffer
28       81 7/subop/compare %eax 0/imm32
29       {
30         74/jump-if-= break/disp8
31         fa/disable-interrupts
32         c6 0/subop/copy-byte *ecx 0/imm8
33         ff 0/subop/increment *Keyboard-buffer:read
34         81 4/subop/and *Keyboard-buffer:read 0x0f/imm32
35         fb/enable-interrupts
36       }
37       # return
38       eb $read-key:end/disp8
39     }
40     # TODO: fake keyboard
41 $read-key:end:
42     # . restore registers
43     59/pop-to-ecx
44     # . epilogue
45     89/<- %esp 5/r32/ebp
46     5d/pop-to-ebp
47     c3/return