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 read/ecx: byte = keyboard buffer's read index
23       8b/-> *0x802c 1/r32/CL  # keyboard-buffer-read
24       # var next-key/eax: byte = *(keyboard buffer + ecx)
25       8a/byte-> *(ecx+0x8030) 0/r32/AL  # keyboard-buffer-data
26       # if (next-key != 0) lock and remove from keyboard buffer
27       81 7/subop/compare %eax 0/imm32
28       {
29         74/jump-if-= break/disp8
30         # TODO: add some instructions in this block to SubX if we ever want to
31         # use bootstrap on baremetal programs
32         fa/disable-interrupts
33         c6 0/subop/copy-byte *(ecx+0x8030) 0/imm8  # keyboard-buffer-data
34         ff 0/subop/increment *0x802c  # keyboard-buffer-read
35         81 4/subop/and *0x802c 0xf/imm32  # keyboard-buffer-read
36         fb/enable-interrupts
37       }
38       # return
39       eb $read-key:end/disp8
40     }
41     # TODO: fake keyboard
42 $read-key:end:
43     # . restore registers
44     59/pop-to-ecx
45     # . epilogue
46     89/<- %esp 5/r32/ebp
47     5d/pop-to-ebp
48     c3/return