On 02/13/18 11:57, Heinrich Rebehn wrote:
Hello List,

I am trying to install current snapshot on a Raspberry 3 B. I have problems 
setting up the serial communication needed to access the installer. I connected 
the serial pins (6,8,10) to the serial port of my PC and set parameters to 
115200/8N1. But I only see garbage on the screen. While googling for a solution 
I found some hints about the Raspi using bizarre baud rates depending on the 
system clock.

Following is my boot/config.txt with the core_freq line added by me:

arm_control=0x200
enable_uart=1
core_freq=250
device_tree_address=0x100
kernel=u-boot.bin

Of course I tried different baud rates, but to no avail. I am using minicom on 
a intel PC running Mac OS.

Is this still a known issue? I found no hints about this in the OpenBSD install 
documents for ARM.

Can someone please help?

-Heinrich

A little searching on the Raspberry Pi Forums finds the following thread. Some things to try, good luck.
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PhilE wrote:
A limitation of UART1 is that the clock varies with the VPU core clock, so you need to set core_freq=250 on the default Raspbian 2016-03-18 firmware, or if you rpi-update (or get the next Raspbian when it is available) then you need to add enable_uart=1 to config.txt (which will also set cpu_freq=250 if ttyS0 is the primary UART)

It seems that "enable_uart" has not been released in the normal channel yet. rpi-update may get it for you, but it might get you a lot of other things as well! I would expect a bump to Raspbian soon, it's been talked about for a while now.

MarkHaysHarris777 wrote:
Also, what specifically does the core_freq=250 affect... L2 cache? whatelse if any? also, is there any other technical side-affect to having the core_freq=250 locked down?

PhilE wrote:
Yes, setting core_freq=250 should eliminate any UART glitching. It will also limit the VPU compute resource, which will mainly affect the new high quality analogue audio output, and could slightly increase the lifetime of the Pi (if there is any change at all).

So I guess the answer for the moment is to keep using "core_freq=250", as you have already found out.

If "core_freq=250" is a problem, and you are not using Bluetooth, you can use:

dtoverlay=pi3-disable-bt
and that will put /dev/ttyAMA0 back on the serial port.

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