Date: Thu, 18 Mar 2021 11:07:36 -0700 From: bob prohaska <fbsd@www.zefox.net> To: freebsd-arm@freebsd.org Subject: Re: RPI4 clock speeds and serial port Message-ID: <20210318180736.GA26853@www.zefox.net> In-Reply-To: <YFONu3Ry0o6VlV92@ceres.zyxst.net> References: <20210318170053.GA26688@www.zefox.net> <YFONu3Ry0o6VlV92@ceres.zyxst.net>
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On Thu, Mar 18, 2021 at 05:28:27PM +0000, tech-lists wrote: > hi, > > On Thu, Mar 18, 2021 at 10:00:53AM -0700, bob prohaska wrote: > > > /boot/msdos/config.txt contains > > > > root@nemesis:~ # more /boot/msdos/config.txt > > [all] > > arm_64bit=1 > > dtparam=audio=on,i2c_arm=on,spi=on > > dtoverlay=mmc > > dtoverlay=disable-bt > > device_tree_address=0x4000 > > kernel=u-boot.bin > > > > [pi4] > > #hdmi_safe=1 > > armstub=armstub8-gic.bin > > > > Can one change the cpu speed without disturbing the serial console > > by using something like > > > > arm_freq=1750 > > > > in config.txt, provided adequate cooling provisions are made? > > I have this config.txt on both a rpi4 stable/13 and main/14. I have a > flirc case on stable/13 and one of those cases that looks like armour > made from solid metal on main/rpi4. > In both cases, the approved 5.1V @3.1W power supply is used. > The highest temp I've seen under load is 72 degC and that's at 25 degC 72 C is rather toasty 8-) > ambient. On both machines my config.txt looks like this: > > arm_control=0x200 > dtparam=audio=on,i2c_arm=on,spi=on > dtoverlay=mmc > dtoverlay=pwm > dtoverlay=disable-bt > device_tree_address=0x4000 > kernel=u-boot.bin > over_voltage=6 > arm_freq=2000 > sdram_freq_min=3200 > > In order to clock it, I need to enable powerd on startup in > /etc/rc.conf: > > powerd_enable="YES" > > Because I also want that higher clock to run as much as possible, I tell > powerd to have an absurdly low trigger to get the clocked speed: > > powerd_flags="-r 1" > > and here's the clocked speed: > > % sysctl -a | fgrep cpu.0 > dev.cpu.0.temperature: 49.6C > dev.cpu.0.freq_levels: 2000/-1 600/-1 > dev.cpu.0.freq: 2000 > dev.cpu.0.%parent: cpulist0 > dev.cpu.0.%pnpinfo: name=cpu@0 compat=arm,cortex-a72 > dev.cpu.0.%location: dev.cpu.0.%driver: cpu > dev.cpu.0.%desc: Open Firmware CPU > > > I'd rather not complicate use of the serial console at this point > > not sure why the serial console would be a factor. I have a > console-wired rpi4 running main/14 and I never considered it. I console > into this machine like this: > > cu -l /dev/cuaU0 -s 115200 > Maybe on FreeBSD it doesn't matter. Pi-related sites report that the mini-UART baudrate is tied to the clock of the GPU, if that changes the baudrate changes too. It wasn't clear to me if the speed-changes to config.txt affected the GPU clock. Apparently not, at least in FreeBSD. Thank you! bob prohaska > -- > J.
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