Add assembler cheat heet

Mikrocomputertechnik/asm.md

+## Load
+
+```asm
+ldr rd, = const   ; load constant
+ldr r1, [r0]      ; load content of address of r0 into r1
+ldr r1, [r0, #8]  ; same with offset
+ldr r1, [r0], #8  ; post-increment
+ldr r1, [r0, #8]! ; pre-increment
+```
+
+Load value defined by dcd
+
+```asm
+MAX DCD 10
+ldr   r3, MAX
+```
+
+## Move
+
+```asm
+mov r0, r1     ; r0 := r1
+mov rd, #const ; const max. 16-Bit, otherwise load
+```
+
+## Add
+
+```asm
+add r0, r1, r2 ; ro = r1 + r2
+add r0, r1     ; ro = r0 + r1
+add r0, #1     ; ro = r0 + 1, for small constants
+```
+
+Set flags while adding
+
+```asm
+adds r0, r1, r2 ; ro = r1 + r2, also sets flags
+```
+
+## Compare
+
+```asm
+; like subtraction, but only sets flags
+cmp r0, r1 ; zero flag set if equal, etc.
+cmp r0, 0  ; compare with constant 
+```
+
+## Branch
+
+Unconditional branch
+
+```asm
+b LABEL ; jump to label
+```
+
+Compare binary numbers
+
+```asm
+; use "cmp r1 r2" always before branch
+; COMMAND ; meaning         C-Code     Flags
+beq LABEL ; equal           r1 == r2   Z = 1
+bne LABEL ; not equal       r1 != r2   Z = 0
+bgt LABEL ; greater         r1 > r2    N = 0
+bge LABEL ; greater equal   r1 => r2   N = 0 or Z = 1
+blt LABEL ; lower           r1 < r2    N = 1
+ble LABEL ; lower equal     r1 =< r2   N = 1 or Z = 1
+```
+
+Branch with flag values
+
+```asm
+; COMMAND ; meaning           Flags
+bcs LABEL ; carry set         C = 1
+bcc LABEL ; carry cleared     C = 0
+bmi LABEL ; minus             N = 1
+bpl LABEL ; plus              N = 0
+bvs LABEL ; overflow set      V = 1
+bvc LABEL ; overflow cleared  V = 0
+beq LABEL ; equal             Z = 1
+bne LABEL ; not equal         Z = 0
+```
+