R32C MCU start up

Question

Hello, 
 I am looking at a program I compiled for the R32C in a binary viewer. 
 I see that at 0xfffffffc the program points at 0, and I know that the offset is special as the "reset vector" according to the documentation. 
 My question is, how exactly does a typical firmqare execute on the R32C, what is the initial PC and the inital MCU start up in general.

JimB · Accepted Answer

I found this for one of the R32C devices (142/145 family), apparently there is a software reset mechanism:

JimB · Answer

I don't believe there is any general rule of thumb about where the R32C might begin executing code. As you mentioned the reset vector is fetched from 0xFFFFFFFC, this value could be any code flash memory location.

JimB · Answer

Only jumping to the reset vector will not produce a reset with the hardware. What I would assume is happening is that the software is getting stuck somewhere expecting the hardware to be in a reset state but it is not. 
 I am not aware of a software reset mechanism on R32C, if this indeed not available then you would need to somehow force a hardware reset, either with some external circuit or you could have the watchdog timer enabled and tight-loop until that times-out.

JimB · Answer

With a debugger you might be able to figure out what doesn't work to accomplish this, but maybe a controlled manual shut-down of the peripherals and then a jump to the reset vector would suffice for your needs. Otherwise I would go with the watch-dog reset, it is simple yet effective.

JimB · Answer

A WDT is just a timer that runs until it expires, and then resets the MCU, unless the timer counter is reset manually by software. The idea is that run-away software can be aborted if regular servicing of the WD is not performed. 
 If your WDT is already running, just tight-loop ("while (1) {}") which will cause a WDT reset eventually. If not already set, you will need to investigate the method to configure and start the timer, which is device dependent. Set up the timer to expire quickly, since no need to sit around waiting. 
 Here are a couple of app-notes on the topic for R32C:

Application Note 
 
 R32C/100 Series How to Use the Watchdog Timer Automatic Count Start 
 PDF 322 KB 日本語 
 Related Files:

Sample Code - R32C/100 Series How to Use the Watchdog Timer Automatic Count Start Rev.1.00 - Sample Code 
 Sample Code - R32C/100 シリーズ ウォッチドッグタイマ自動起動機能の使い方

Feb 24, 2012

Application Note 
 
 Watchdog Timer (REJ05B1211-0100) 
 PDF 110 KB 
 Related Files:

Sample Code

Mar 5, 2010

And here is another useful app-note if you care to know whether the reset was due to WDT or other reset source:

Application Note 
 
 How to Determine Reset Source 
 PDF 1.56 MB 日本語 
 Related Files:

Sample Code - How to Determine Reset Source - Sample Code 
 Sample Code - ディレイドワンショット出力 - Sample Code

Dec 29, 2009

R32C MCU start up

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