gcc for Andes compile 出來的 assembly

為了要做 24-bit signed integer to 32-bit signed integer 的 signed extension 測試，我寫了以下的一小段 code 來測試, 在這裡順便稍微提一下 optimization, 我們先看 c code:

void testSign()
{
        unsigned int test=0x00800000;
        int test_s;
        test_s = ((int)test << 8 ) >> 8;
}

除去 prologue 或 epilogue 的部份，我們來看主體:

00000614 <testSign>:
......
 61c:   46 00 08 00     sethi $r0,#2048
 620:   14 0e 7f fd     swi $r0,[$fp+#-12]
 624:   04 0e 7f fd     lwi $r0,[$fp+#-12]
 628:   40 00 20 08     slli $r0,$r0,#0x8
 62c:   90 08           srai45 $r0,#0x8
 62e:   14 0e 7f fe     swi $r0,[$fp+#-8]

解釋如下：

sethi $r0,#2048

$r0 = 0x00800000

swi $r0,[$fp+#-12]

把 $r0 存回 test 的儲存空間

lwi $r0,[$fp+#-12]

把變數 test 值抓到 $r0

slli $r0,$r0,#0x8

把 $r0 做 logical left shift by 8 bits, $r0 = 0x80000000

srai45 $r0,#0x8

把 $r0 做 arithmetic right shift by 8 bits, $r0 = 0xff800000

swi $r0,[$fp+#-8]

存回 test_s 的儲存空間。

而如果我們把這個 c code 改成如下：

int testSign(unsigned int value)
{
        return ((int)test << 8) >> 8;
}

產生出來的 assembly 就會變成:

000005f8 <testSign>:
 5f8:   40 00 20 08     slli $r0,$r0,#0x8
 5fc:   90 08           srai45 $r0,#0x8
 5fe:   dd 9e           ret5 $lp

這個版本完全沒有任何 local variables, 傳入的參數也只有一個, 當傳入參數
只有一個的時候, 會使用 $r0 這個暫存器傳入, 回傳值也是在 $r0 回傳,
所以這樣子最省空間了,也是我們 assembly programmer 會寫出來的樣子。注意
如果沒有做 (int) 的 explicit cast, 編譯器並不會使用 srai45 這個
arithmetic right shift 指令製造 signed extension, 即便是最後的回傳值是
有號數。

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Emacs 的 org-googlecl 會把標題的 $ 吃掉

在上一篇「超便宜的 TI C6670 EVM, 只要 USD$599!」中，原本的文章因為 $ 在標題中被吃掉，所以變成了「超便宜的 TI C6670 EVM, 只要 USD99!」，想必標題相當吸引人，呵呵。

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超便宜的 TI C6670 EVM, 只要 USD$599!

參考連結: http://www.ti.com/tool/tmdxevm6670
這是 TI 的 TMS320C6670 EVM 的連結，這一顆 DSP 擁有四個 C66x 的核心，每一個核心都可執行 SIMD 指令，可以同時執行 8 組 32-bit 指令。TI 稱呼這個叫做 static VLIW, i.e. Very Long Instruction Word. 另外, C6670 有 Turbo encoder/decoder coprocessor、Viterbi decoder coprocessor、CDMA 用的 RAKE 加速器，還有 FFT coprocessor 等，頗適合拿來實作 WCDMA/CDMA2000/LTE 等各種 cellular communication 的基地台。當然，要拿來其他通訊模式也非常 powerful. 這麼強大的一顆 DSP, EVM 含 emulator 只要 USD$599 喔！

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SimPy slides in our company and PyHUG meeting

This is my presentation on discrete-event simulation given to engineers in our company and PyHUG, which is Python Hsinchu User Group. I think it might be useful for somebody on the Internet.
https://docs.google.com/open?id=0B0rtbYTzC_{ZWN2Y5MmY4M2ItYzJkYy00ZTA2LWI5N2UtNmUxNjI5YzNjZTg0}

http://dl.dropbox.com/u/31960195/Introduction-to-SimPy-20111017-PyHUG.pdf

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Improvement on matlab-emacs

Modification to matlab-cellbreak-face

Current cvs code for matlab.el does not handle cellbreak-face correctly. It cannot distinguish between %% and %%%%, but matlab-shell-run-cell can function well. But fontifying not well is still annoying, so we need to modify it. In matlab.el, find the following lines to modify from:

;; Cell mode breaks get special treatment
'("^\\s-*\\(%%[^\n]*\n\\)" (1 matlab-cellbreak-face append))

Change it to:

;; Cell mode breaks get special treatment
'("^\\s-*\\(%%[^%\n]*\n\\)" (1 matlab-cellbreak-face append))

Evaluate cell and advance (C-S-return)

In MATLAB editor, we can press C-S-return to perform "evaluate cell and advance" function. Minor modification to matlab.el can make it happen. You can just add the following code snippet to your .emacs file.

(require 'matlab-load)
(defun matlab-goto-next-cell ()
  (interactive)
  (re-search-forward "^%%[^%\n]"))

(require 'matlab)
(define-key matlab-mode-map [(meta control F)] 'matlab-goto-next-cell)
(defun matlab-run-cell-and-go ()
  (interactive)
  (progn
    (save-excursion
      (matlab-shell-run-cell))
    (matlab-goto-next-cell)))
(define-key matlab-mode-map [(meta shift return)] 'matlab-run-cell-and-go)

The example for running matlab cell mode is like this:

a = [1,2,3];

c = [4,5,6];

%% This is first cell

d = a * c';

%%%% This is not a cell

b = [3,2,1];

%% Another cell

c = a + b;

kkk

After pressing three <C-S-return>, the matlab-shell screen will look like:

                            < M A T L A B (R) >
                  Copyright 1984-2010 The MathWorks, Inc.
                Version 7.12.0.635 (R2011a) 64-bit (maci64)
                               March 18, 2011

 
  To get started, type one of these: helpwin, helpdesk, or demo.
  For product information, visit www.mathworks.com.
 
>> addpath('/Users/jjhuang/elisp/matlab-emacs/toolbox','-begin'); rehash; emacsinit('emacsclient -n');
>> , a = [1,2,3];, c = [4,5,6];, 
>> , a = [1,2,3];, c = [4,5,6];, d = a * c';, b = [3,2,1];, 
>> , d = a * c';, b = [3,2,1];, c = a + b;, kkk, 
??? Undefined function or variable 'kkk'.
 
>> 

Okay, now matlab-emacs for me is more convenient right now. Hope you enjoy it!

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