ARM Instruction Set
  • PSR(Program Status Register)
  • Condition field
  • −x = not(x)+1 and computes a−b as a+not(b)+1.
  • The carry flag is set according to this addition.
  • C set = higher or the same
  • The same: 1-1=1+not(1)+1=00000001+11111110+1=1(carry set), 00000000
  • Lower: 1-2=1+not(2)+1=00000001+11111101+1=0(carry clear), 11111111
  • Arithmetic Operations
SBC r0, r1, r2 r0 := r1-r2+C-1 The SBC (Subtract with Carry) instruction subtracts the value of Operand2 from the value in Rn. If the carry flag is clear, the result is reduced by one.
LDR R0, [R1, R2]

  • Stack
    • Ascending vs. Descending
    • Full v.s. Empty
  • DMB ensures that all explicit memory accesses before the DMB instruction complete before any explicit memory accesses after the DMB instruction start.
  • This ensures correct ordering between two memory accesses.
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