# Lab1 Note ###### tags: `NCTU` `MPSL` ### Question 實驗課問題 #### Question 1 (for lab 3-1): - **What is the IT-block for ARM Assembly? ARM 組合語言中的 IT-block 指的是甚麽？** The `IT` (If-Then) instruction makes up to four following instructions (the *IT block*) conditional. The conditions can be all the same, or some of them can be the logical inverse of the others. With IT instruction, you can specify condition code for up to 4 instructions. For each instruction, you specify if it's part of the If (T) or Else (E). #### For example: ```c ITTET EQ ADD r0,r0,r0 ADD r1,r0,r0 ADD r2,r0,r0 ADD r3,r0,r0 ``` #### Will actually translate to: ```c ADDEQ r0,r0,r0 (Always if for 1st one) ADDEQ r1,r0,r0 (T for 2nd one) ADDNE r2,r0,r0 (E for 3rd one) ADDEQ r3,r0,r0 (T for 4th one) ``` #### APSR - Application Program Status Register ( N Z C V ) - **What are the condition code suffixes of ARM instruction? ARM 指令的條件碼後綴是什麼？** ADDS、LDRB、BEQ、BVS - **What is the difference between instruction ADD and ADDS? 指令ADD與ADDS之間有何差別？** ADD是一般的加法，ADDS會更新N, Z, C and V 4個 flags #### Question 2 (for lab 3-2): - **How to detect overflow by software? That is, using an algorithm or logical operation to detect overflow. 如何通過軟體檢測溢位？即使用演算法或是邏輯判斷的方式偵測溢位。** ``` BVS 、 Signed bit ``` - **Question 3 (for lab 3-2): Does ARMv7-M provide any hardware support on overflow detection? ARMv7-M 是否在溢出檢測方面提供任何硬體支持？** ``` V flag ``` ### Demo Question #### **Question (3-1)** >請使用 asm code 回答下述問題 1. **請說明如何計算變數 X, Y 之間的漢明距離，如何統計有幾個相異的 bits?** ``` eor (xor) 然後計算有幾個1 ``` 2. 請說明程式是如何從 hamm 函數跳回到 main 函數中 ``` bl hamm 在branch的同時將下筆指令的address存在LR暫存器， bx lr 即可跳回來。 ``` --- #### **Question (3-2)** > 請說明實作方式或以 asm code 回答下述問題 1. 請說明程式是如何計算 Fn ```R3 = R1 + R2 ...``` 2. 請說明如何判斷 N 值是否超出範圍 (100<N or N<0) ```用 cmp ``` ---