The reason given in the book is
C language does not have the conditions to run immediately after power-on:
Global variables are not initialized, the system stack is not initialized, and so on.
Why doesn't the C language of the MCU start the code? (keil comes with startup code, but it will go wrong if it is not handled well, generally it doesn't matter.)
It seems to be related to the compiler, and today I saw a more convincing answer.
When the compiler compiles the C language, it will add a fixed code **.O file, which is a file that comes with the compiler.
That is, the first instruction executed by C language is not the main entry function of C language, but the instruction of **.O.
The MAIN function entry is called after the instruction is initialized, but it cannot be run directly. We must write a piece of code to replace it.
So we often see some super simple startup code:
AREA |DATA|,CODE,READONLY
ENTRY
Ldr r13, =0 x1000
Im port ledMain
b ledMain
END
As above.
Laptop power adapter charger for Dell:
| Laptop Model | Adapter Output |
| Latitude E5400 E5410 E5500 E5510 | 19.5v 4.62a, 7450 |
| Studio XPS 16 (1645)1640 1645 1647 | 19.5v 4.62a, 7450 |
| Studio XPS M1645 M1647 | 19.5v 4.62a, 7450 |
| XPS 14 15 17 L501x L502x L702x L702x | 19.5v 4.62a, 7450 |
| Inspiron 1464 1564 1764 | 19.5v 4.62a, 7450 |
| Inspiron 1525 1440 1526 | 19.5v 3.34a, 7450 |
| Precision M4600 M6600 | 19.5v 6.7a, 7450 |
| Inspiron N5050 N4010 N5110 | 19.5v 3.34a, 7450 |
| Inspiron 14Z-N411Z 13Z N311Z | 19.5v 4.62a, 7450 |
| Inspiron 1545 | 19.5v 3.34a, 7450 |
| Latitude E5420 E5530 E5430 E6420 | 19.5v 4.62a, 7450 |
| Inspiron 1440 1525 1526 1545 1750 | 19.5v 3.34a, Octagon tip |
| Inspiron 1300 B120 B130 | 19v 3.16a/3.42, 5525 |
| Inspiron 1525 1526 1545 | 19.5v 3.34a, 7450 |
| Studio 1440 1440n 1440z 14z 14zn | 19.5v 3.34a, 7450 |
| Latitude E4300 E4310 | 19.5v 4.62a, 7450 |
| Inspiron 13Z 13ZD 13ZR M301 M301z M301ZD M301ZR N301 | 19.5v 3.34a, 7450 |
| Inspiron N301Z N301ZD N301ZR | 19.5v 3.34a, 7450 |
| Studio 1535 1536 1555 1557 1558 | 19.5v 4.62a, 7450 |
| Latitude E5420 E5520 E6430 E6530 E6420 E6520 | 19.5v 4.62a, 7450 |
| Inspiron Mini 10 10v 1010 1010n 1010v 1011 1011n 1011v | 19v 1.58a, 5517 |
| Inspiron 14V 14VR M4010 N4020 N4030 | 19.5v 4.62a, 7450 |
| Inspiron N4110 N5110 N7110 M5010 | 19.5v 3.34a, 7450 |
| 630M 640M E1405 | 19.5v 4.62a, 7450 |
| Inspiron 15-3521 17-3721 | 19.5v 3.34a, 7450 |
| Latitude 120L | 19.5v 3.34a, 7450 |
| Vostro 1710 1710n 1720 1720n | 19.5v 4.62a, 7450 |
| Vostro 1500 1700 Inspiron 1520 1521 1720 | 19.5v 4.62a, 7450 |
| Vostro 1400 1420 PP26L | 19.5v 3.34a, 7450 |
| Latitude D410 | 19.5v 3.34a, 7450 |
| Inspiron 1120, 1121, M101 | 19.5v 3.34a, 7450 |
| Inspiron Mini 1012 1018 | 19v 1.58a, 5517 |
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