.global main # makes label "main" globally known
.text # Instructions follow
.align 2 # Align instructions to 4-byte words
main: movi r16,0x47 # Load the hexadecimal value 41
# to register r16
loop: mov r4,r16 # Copy to r4 from r16
nop # (later changed to call hexasc)
nop # (later changed to mov r4,r2)
movia r8,putchar # copy subroutine address to a register
callr r8 # call subroutine via register
addi r16, r16,1 # Add 1 to register r16
andi r16, r16, 0x7f # mask with 7 bits
ori r16, r16, 0x20 # set a bit to avoid control chars
br loop # Branch to loop
.end # The assembler will stop reading here
foo bar bletch # comes after .end - ignored
I can understand everything, I think, except how the two instructions andi and ori work in this case. ori appears to make so that the ASCII 20 positions forward is printed but why and how?