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sparkfun / OpenLog

Open Source Hardware Datalogger
https://www.sparkfun.com/products/9530
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Reduce clock speed to 8 MHz, can not properly log @ 115200 baud rate #218

Closed ewan1983 closed 6 years ago

ewan1983 commented 6 years ago

I use Openlog to connect with my board, and got a lot of small files, seems Openlog have been keep resetting. I suspect it was a power issue as my board have only 3V supply, and it might not be enough to drive 16MHz clock as in default Openlog.

So I modified the F_CPU configuration in boards.txt to 8MHz uno.build.f_cpu=8000000L, and in setup(void) function of OpenLog_Minimal firmware, I add
clock_prescale_set(clock_div_2);

The result is that I can only correctly log one character, if send more than one character only the first one is correctly logged, and the rest are corrupted. The problem is probably in serial rx part, but I haven't figure out what exactly the problem is.

The setting_uart_speed is 115200, when this problem happens. If I change the baud rate to 57600, everything is fine. So I thought high baud rate got problem, then I change the baud rate to 200000, it also works! Only 115200 got problem, WTF?

However, at 8 MHz and 200000 baud rate, I still have multiple small files, and have many data missing in-between.

alexpirine commented 6 years ago

Hi,

Have you solved the issue?

marshalltaylorSFE commented 6 years ago

I ran into a similar issue on another project using an 8MHz processor and 115200. The problem is that there simply isn't enough time to service the ISR between bytes. By the time the serial ISR completes, we're mid-way into the next byte. Thus garbage.

If you can cause your serial transmitter to emit two stop bits instead of one, it gives an extra symbol's worth of time between the bytes. With my test, this was enough to get the data correctly. Otherwise, get the voltage up so you can run at 16MHz.

alexpirine commented 6 years ago

Which voltage is required for 16 MHz? I currently use 3.3 V and sometimes it works, sometimes I get plenty of log files and lose data in between...

alexpirine commented 6 years ago

Is it possible to set an arbitrary clock speed like 12 MHz?

marshalltaylorSFE commented 6 years ago

3.3V should be fine. ewan1983's issue is exactly a baud related problem... if you're getting solid chunks of data, then just missing some, that sounds like a different issue entirely. Can you post another issue with more information about your setup that causes intermittent lost of data?

I explored 12MHz for my other project. There's no easy way to scale things to 1.5x, so it would take a bit of research and modification to the project and maybe even the board files in Arduino.

JensGrabner commented 6 years ago

Here is a calculator for that: http://wormfood.net/avrbaudcalc.php?bitrate=57.6k%2C76.8k%2C115.2k&clock=8%2C+12%2C+16&databits=8 I use 3V3 with 12MHz Clock a Baud Rate 115.2k (U2Xn = 1) is good ... and 3V3 with 8MHz Clock a Baud Rate 76.8k (U2Xn = 1) is also good.

alexpirine commented 6 years ago

Thanks for the tips. I am running at 3.3V and 115200 baud rate with the "minimal" firmware.

And I get multiple open log files instead of just one.

I will be happy to open a new issue if this not related to the clock (which is at 16 MHz by default from my understanding) / voltage.