System Software

--- tags: 大二, 筆記 --- # System Software ## SIC + 假想電腦 + 有 XE 版本，為進階版 + SIC/XE 可相容 SIC 的指令 (upward compatible) ### Memory + 1 byte = 8 bit + 1 word = __3 bytes__ + Total $2^{15}$ bytes + byte addressable ### Registers + | Mnemonic | Number | Special use | | -------- | ------ | ---------------- | | A | 0 | Accumulator | | X | 1 | Index register | | L | 2 | Linkage register | | PC | 8 | Program counter | | SW | 9 | Status word | ### Data Formats + Integers : 24 bit + Characters : 8 bit ASCII codes + No floating-point ### Instruction Formats ``` 8 1 15 +-----------+-----+--------------------------+ | opcode | X | address | +-----------+-----+--------------------------+ ``` ### Address mode + | Mode | Indication | TA | | ------- | ---------- | -------------- | | Direct | x=0 | = address | | Indexed | x=1 | = address+ (X) | ## SIC/XE ### Memory + can address 1MB ($2^{20}$ bytes) ### Registers + | Mnemonic | Number | Special use | | -------- | ------ | ---------------- | | A | 0 | Accumulator | | X | 1 | Index register | | L | 2 | Linkage register | | PC | 8 | Program counter | | SW | 9 | Status word | | B | 3 | Base | | S | 4 | General working | | T | 5 | General working | | F | 6 | Floating-point | ### Data Formats + 有小數可以用了! ``` 1 11 36 +---+----------------+---------------------+ | s | exp | frac | +---+----------------+---------------------+ ``` + Value = $(-1)^s0.f*2^{(exp-1024)}$ ### Instruction Formats + Format 1 : 1 byte + ``` 8 +--------------+ | opcode | +--------------+ ``` + Format 2 : 2 bytes + ``` 8 4 4 +--------------+---------+---------+ | opcode | r1 | r2 | +--------------+---------+---------+ ``` + Format 3 : 3 bytes + ``` 6 1 1 1 1 1 1 12 +-------------------------------------+ | op |n|i|x|b|p|e| disp/address | +-------------------------------------+ e = 0 ``` + Format 4 : 4 bytes + ``` 6 1 1 1 1 1 1 20 +------------------------------------------+ | op |n|i|x|b|p|e| address | +------------------------------------------+ e = 1 ``` + 定址模式 + PC relative : b=0, p=1 + 會先檢查這個 + Base relative : b=1, p=0 + 再檢查這個 + Direct : b=0, p=0 + (+)op c + (+)op m + c是常數 + Indexed : n=1, i=1, x=1 + (+)op m, X + Immediate : n=0, i=1, x=0 + (+)op #c + c是常數 + (+)op #m + __要檢查 PC-relative 和 Base-relative__ + Indirect : n=1, i=0, x=0 + (+)op @m + (+)op @c + Simple : n=0, i=0 or n=1,i=1 + n=0, i=0 : 相容 SIC 用的 , op m + (+)op m + (+)op c ## Assembler ### 重要功能 + location counter + Write object program + 2 pass ### object program + Header record : + H + Program name + Starting address + Length of object program in bytes + Text record + T + Starting address + Length in bytes + Object code + End record + E + Address of first executable instruction ### Algorithm and data structures + Two-pass assembler + OPTAB + SYMTAB + | Label | Addr | | ------ | ---- | | FIRST | 1000 | | CLOOP | 1003 | | ENDFIL | 1015 | | ... | ... | + LOCCTR + Intermedia file + 在pass 1 與 pass 2 之間的溝通檔案 + 放有 address, error indicators 等資料 ### Psudeo code > 見課本 ## SIC/XE Assembler + 更多定址模式 & instruction formats + Program Relocation + START 0 + SIC/XE 指令對應 + | | | | ------------------------- | -------- | | Immediate | `op #c` | | Indirect | `op @m` | | PC-relative/Base-relative | `op m` | | Extended format | `+op m` | | Indexed | `op m,x` | + Register-to-register instructions + Keep the register name and value in __SYMTAB__ + Large memory + multiprogamming and program reallocation ### Address translation + PC-relative : -2048 ~ 2047 + Base-relative : 0 ~ 4095 + Assembler 會先試 PC-relative, 失敗才試 Base-relative + 如果還不夠用就用 format 4，有20 bit + ex 1 : + ```assembly ;10 1000 FIRST STL RETADR ;17202D ;RETADR = 30h; STL = 14h ``` + disp = RETADR - (PC) = 30 - 3 = 2Dh + opcode = 00010100b + nixbpe = 110010 + ``` opcode nixbpe disp +---------------------------------+ | 000101 |110010| (02D)h | +---------------------------------+ (17202D)h ``` + ex 2 : + ```assembly ;40 0017 J CLOOP ;3F2FEC ;CLOOP = 6; J = 3Ch ``` + disp = 6 - 1A = -14 = -(0000 0001 0100)b = (1111 1110 1100)b = (FEC)b + opcode = 00111100 + nixbpe = 110010 + ``` opcode nixbpe disp +---------------------------------+ | 001111 |110010| (FEC)h | +---------------------------------+ (3F2FEC)h ``` + ex 3 : + ```assembly ;160 104E STCH BUFFER,X ;57C003 ;(B) = 0033; opcode = 54; BUFFER = 0036 ``` + disp = 0036 - 104E(PC) = -1018 <- 超過了 + disp = 0036 - 0033(B) = 3 + __不用處理 X __ + nixbpe = 111100 + ``` opcode nixbpe disp +---------------------------------+ | 010101 |111100| (003)h | +---------------------------------+ (57C003)h ``` + ex 4 : + ```assembly ;12 0003 LDA #LENGTH ;69202D ;opcode = 68; LENGTH = 0033 ``` + __有變數操作，要用relative__ + disp = 0033 - 0006 = 02D + nixbpe = 010010 + ``` opcode nixbpe disp +---------------------------------+ | 011010 |010010| (02D)h | +---------------------------------+ (69202D)h ``` + ex 5 : + ```assembly ;70 002A J @RETADR ;3E2003 ;opcode = 3C ``` ### Program relocation + HOW TO : + `COPY START 0` + In SIC/XE : + Format 1 2 3 + Not affect + Format 4 + 要改 + In SIC : + Format 3 with address field + 要改 + 要怎麼改? + Modification record + M + Starting loc of addr to be modified + length to be modified, in half-bytes + e.g. : + `M 000007 05` + 真實況下沒有空白 + 雖然打7，但實際上是7.5 ### Symbol-defining #### Label v.s. Symbols + label : 連結 addr + symbols : 似 C 裡的 `#define` ，可以定義很多東西 #### Usage + `symbol EQU value` #### How it works? 1. pass 1 + 遇到直接先寫入 SYMTAB 2. pass 2 + 把值讀回來 ### Program blocks > 把變數宣告和程式碼本身分開，讓 assembler 自行排列，可避免存取過遠的位置及增加讀取效率 + 預設為 default block + `USE CBLCK` + 每個 block 都有自己的 LOCCTR + Pass 1 : + 針對每個 block 計算相對於其開頭的 address + Pass2 : + 計算 object code + 對於 abslute symbol (非相對)，沒有 block number + e.g : + `107 1000 MAXLEN EQU BUFEND-BUFFER` + ex : + ```assembly ;20 0006 0 LDA LENGTH ;032060 ;~~~~ ;100 0003 1 LENGTH RESB 4096 ``` + LENGTH = (block 1 start)+0003 = 0066+0003=0069 + LOCCTR = (block 0 start)+0009 = 0009 + PC-relative : disp = 0069 - 0009 = 0060 + Object code 沒有被動到 + `USE` 的時候 Text record 會開新的一行(個) ### Control section + 相當於 Java 裡的 import 及 JavaScripts 的 export + external reference === import + `CSECT` tag 可供全域跳躍 + 一定要用 format 4 + Define record : + D + Name1 relative address1 + Name2 relative address2 ... + Refer record + R + Name1 Name2 ... + Modification record + M + start address + length to modify + +/- + external symbol