AIBOU KAKASHI

昨天母公司安排我去面談，其中一位面談者問我一個問題是Embeded processor無法開機的問題。

其實，問題本身好像很單純，但是答案可以說上一個多小時。

(1) CLOCK problem

The processor needs a stable clock for operation. The clock shall be within the allow range。

如果clock不對， 通常 CS0 signal會出不來。

(2) DC Power

There are Core power and I/O power in modern processor design.

The power sequence described in the datasheet shall be followed .

(3)  RESET

The reset signal shall be long enough to make sure the reset is executed before

the boot sequence.

(4)Boot strap pin

Some processors have dedicated strap pins for some setting.

Most of them might be sampled at the rising edge of reset signal.

(5) Bus endianship

The endianship shall be correct in the boot device.

The LSB of Address bus might be A0 (8-bit) A1(16-bit) or A2( 32-bit)

or A0 (if there is internal bus switch)

The Data bus orienattion, check powerPC for reference.

(6) Boot code (or BIOS) FLASH (or ROM).

The connection to FLASH device is also another issue.

Some of the FLASH device have different LSB pin for address bus.

(7) Bus collision

Some of the peripherial if not properly controlled or well decoded

will output data in the data bus and corrupt the data bus.

(8) F/W error

Correct init. sequence shall be applied to have a sucessful boot.

(9) Signal integrity

Good layout and timing will give good result.

(10) Others

Sometimes, there is still unknown problem other than design

Such as bad soldering, Bad chip ....

總之，光是回答這個問題，就可以寫一本小冊子。問我的人，可能以為我要找個工程師的工作，派怕我年資那麼久，搞不好連這個都不懂，當我在回答時，只見他一直在看手錶，也沒阻止我不要說下去。感覺不是很好。

不過這個問題，只能說『大哉問』。