guillaumekh
Posts: 10
Joined: Fri Dec 21, 2018 6:42 pm

Voltage reduction under thermal throttling

Fri Mar 29, 2019 5:33 pm

The Frequency management and thermal control chapter in documentation mentions the following (emphasis mine) :
As the device approaches the limit, various frequencies and sometimes voltages used on the chip (ARM, GPU) are reduced.
For Raspberry Pi 3 Model B+, [...] when the soft limit is reached, the clock speed is reduced from 1.4GHz to 1.2GHz, and the operating voltage is reduced slightly.
What's the range of that voltage reduction ? How low can it go ?

jahboater
Posts: 4595
Joined: Wed Feb 04, 2015 6:38 pm

Re: Voltage reduction under thermal throttling

Fri Mar 29, 2019 7:40 pm

guillaumekh wrote:
Fri Mar 29, 2019 5:33 pm
What's the range of that voltage reduction ? How low can it go ?
I am seeing 0.1V drop roughly when the CPU freq drops from 1.4GHz to 1.2GHz.
This is the log when running the pathological stress test cpuburn53. Unfortunately the thermal management of the Pi3B+ is so good that it barely gets to throttle with the limit set to 70.
Note the 1.2V reading is at idle.

Code: Select all

temp_soft_limit=70
Time      Temp    CPU          Health         Vcore
19:27:10 36.5'C  600MHz 00000000000000000000 1.2V
19:27:20 39.2'C 1400MHz 00000000000000000000 1.3312V
19:27:31 42.9'C 1400MHz 00000000000000000000 1.3312V
19:27:41 44.0'C 1400MHz 00000000000000000000 1.3312V
19:27:51 45.6'C 1400MHz 00000000000000000000 1.3312V
19:28:02 47.2'C 1400MHz 00000000000000000000 1.3312V
19:28:12 48.3'C 1400MHz 00000000000000000000 1.3312V
19:28:22 49.9'C 1400MHz 00000000000000000000 1.3312V
19:28:33 51.5'C 1400MHz 00000000000000000000 1.3312V
19:28:43 52.6'C 1400MHz 00000000000000000000 1.3312V
19:28:53 53.7'C 1400MHz 00000000000000000000 1.3312V
19:29:04 54.8'C 1400MHz 00000000000000000000 1.3312V
19:29:14 55.8'C 1400MHz 00000000000000000000 1.3312V
19:29:24 56.9'C 1400MHz 00000000000000000000 1.3312V
19:29:35 58.0'C 1400MHz 00000000000000000000 1.3312V
Time      Temp    CPU          Health         Vcore
19:29:45 58.5'C 1400MHz 00000000000000000000 1.3312V
19:29:55 59.1'C 1400MHz 00000000000000000000 1.3312V
19:30:06 60.1'C 1400MHz 00000000000000000000 1.3312V
19:30:16 60.1'C 1400MHz 00000000000000000000 1.3312V
19:30:26 61.2'C 1400MHz 00000000000000000000 1.3312V
19:30:36 62.3'C 1400MHz 00000000000000000000 1.3312V
19:30:47 62.8'C 1400MHz 00000000000000000000 1.3312V
19:30:57 63.4'C 1400MHz 00000000000000000000 1.3312V
19:31:07 64.5'C 1400MHz 00000000000000000000 1.3312V
19:31:18 64.5'C 1400MHz 00000000000000000000 1.3312V
19:31:28 65.5'C 1400MHz 00000000000000000000 1.3312V
19:31:38 65.5'C 1400MHz 00000000000000000000 1.3312V
19:31:49 66.1'C 1400MHz 00000000000000000000 1.3312V
19:31:59 66.6'C 1400MHz 00000000000000000000 1.3312V
19:32:09 67.1'C 1400MHz 00000000000000000000 1.3312V
Time      Temp    CPU          Health         Vcore
19:32:20 66.6'C 1400MHz 00000000000000000000 1.3312V
19:32:30 68.2'C 1400MHz 00000000000000000000 1.3312V
19:32:40 68.8'C 1400MHz 00000000000000000000 1.3312V
19:32:51 69.3'C 1400MHz 00000000000000000000 1.3312V
19:33:01 69.3'C 1400MHz 00000000000000000000 1.3312V
19:33:11 69.8'C 1400MHz 10000000000000000000 1.3312V
19:33:21 69.8'C 1400MHz 10000000000000000000 1.2313V
19:33:32 69.8'C 1200MHz 10000000000000000000 1.3312V
19:33:42 70.4'C 1400MHz 10000000000000000000 1.3312V
19:33:52 69.8'C 1400MHz 10000000000000001000 1.3312V
19:34:03 69.8'C 1200MHz 10000000000000000000 1.3312V
19:34:13 69.8'C 1200MHz 10000000000000001000 1.2313V
19:34:23 69.8'C 1200MHz 10000000000000000000 1.2313V
19:34:33 70.4'C 1400MHz 10000000000000001000 1.3312V
19:34:44 69.8'C 1200MHz 10000000000000001000 1.3312V
Time      Temp    CPU          Health         Vcore
19:34:54 69.8'C 1200MHz 10000000000000000000 1.3312V
19:35:04 70.4'C 1200MHz 10000000000000001000 1.3312V
19:35:15 70.4'C 1400MHz 10000000000000001000 1.3312V
19:35:25 69.8'C 1400MHz 10000000000000001000 1.3312V
19:35:35 70.4'C 1400MHz 10000000000000001000 1.2313V
19:35:46 70.9'C 1200MHz 10000000000000000000 1.2313V
19:35:56 70.4'C 1400MHz 10000000000000000000 1.3312V
19:36:06 69.8'C 1400MHz 10000000000000001000 1.2313V
19:36:17 70.9'C 1400MHz 10000000000000001000 1.3312V
19:36:27 70.4'C 1200MHz 10000000000000001000 1.2313V
19:36:37 69.8'C 1400MHz 10000000000000001000 1.2313V
19:36:47 69.8'C 1400MHz 10000000000000001000 1.3312V
19:36:58 70.4'C 1200MHz 10000000000000000000 1.2313V
19:37:08 70.4'C 1200MHz 10000000000000000000 1.2313V
19:37:18 69.8'C 1400MHz 10000000000000001000 1.2313V
Last edited by jahboater on Fri Mar 29, 2019 7:45 pm, edited 1 time in total.

guillaumekh
Posts: 10
Joined: Fri Dec 21, 2018 6:42 pm

Re: Voltage reduction under thermal throttling

Fri Mar 29, 2019 7:44 pm

Nice thanks @jahboater

jahboater
Posts: 4595
Joined: Wed Feb 04, 2015 6:38 pm

Re: Voltage reduction under thermal throttling

Fri Mar 29, 2019 7:51 pm

Here is another run with the temp soft limit set to the default 60C.
Again its not showing any signs of it throttling further. I suspect with poor cooling (in a small case and/or in a hot country) it will throttle further and the voltage will go down further - but I cant achieve that here.

Code: Select all

Time      Temp    CPU          Health         Vcore
19:41:11 50.5'C  600MHz 10000000000000000000 1.2V
19:41:21 53.7'C 1400MHz 10000000000000000000 1.3250V
19:41:32 55.8'C 1400MHz 10000000000000000000 1.3250V
19:41:42 57.5'C 1400MHz 10000000000000000000 1.3250V
19:41:52 58.5'C 1400MHz 10000000000000000000 1.3250V
19:42:03 60.1'C 1400MHz 10000000000000000000 1.2313V
19:42:13 60.1'C 1200MHz 10000000000000000000 1.3250V
19:42:23 60.1'C 1200MHz 10000000000000001000 1.3250V
19:42:34 60.1'C 1200MHz 10000000000000001000 1.2313V
19:42:44 60.7'C 1200MHz 10000000000000001000 1.2313V
19:42:54 60.1'C 1200MHz 10000000000000001000 1.2313V
19:43:05 60.7'C 1200MHz 10000000000000001000 1.2313V
19:43:15 61.2'C 1200MHz 10000000000000001000 1.2313V
19:43:25 61.8'C 1200MHz 10000000000000001000 1.2313V
19:43:35 61.2'C 1200MHz 10000000000000001000 1.2313V
Time      Temp    CPU          Health         Vcore
19:43:46 61.8'C 1200MHz 10000000000000001000 1.2313V
19:43:56 62.3'C 1200MHz 10000000000000001000 1.2313V
19:44:06 62.3'C 1200MHz 10000000000000001000 1.2313V
19:44:17 62.3'C 1200MHz 10000000000000001000 1.2313V
19:44:27 62.3'C 1200MHz 10000000000000001000 1.2313V
19:44:37 62.3'C 1200MHz 10000000000000001000 1.2313V
19:44:48 63.4'C 1200MHz 10000000000000001000 1.2313V
19:44:58 62.8'C 1200MHz 10000000000000001000 1.2313V
19:45:08 62.8'C 1200MHz 10000000000000001000 1.2313V
19:45:18 63.4'C 1200MHz 10000000000000001000 1.2313V
19:45:29 63.4'C 1200MHz 10000000000000001000 1.2313V
19:45:39 63.4'C 1200MHz 10000000000000001000 1.2313V
19:45:50 63.4'C 1200MHz 10000000000000001000 1.2313V
19:46:00 62.8'C 1200MHz 10000000000000001000 1.2313V
19:46:10 63.4'C 1200MHz 10000000000000001000 1.2313V
Time      Temp    CPU          Health         Vcore
19:46:20 63.9'C 1200MHz 10000000000000001000 1.2313V
19:46:31 63.9'C 1200MHz 10000000000000001000 1.2313V
19:46:41 63.4'C 1200MHz 10000000000000001000 1.2313V
19:46:51 64.5'C 1200MHz 10000000000000001000 1.2313V
19:47:02 63.4'C 1200MHz 10000000000000001000 1.2313V
19:47:12 63.9'C 1200MHz 10000000000000001000 1.2313V
19:47:22 63.4'C 1200MHz 10000000000000001000 1.2313V
19:47:32 63.9'C 1200MHz 10000000000000001000 1.2313V
19:47:43 64.5'C 1200MHz 10000000000000001000 1.2313V
19:47:53 63.9'C 1200MHz 10000000000000001000 1.2313V
19:48:03 64.5'C 1200MHz 10000000000000001000 1.2313V
19:48:14 64.5'C 1200MHz 10000000000000001000 1.2313V
19:48:24 63.9'C 1200MHz 10000000000000001000 1.2313V
19:48:34 65.0'C 1200MHz 10000000000000001000 1.2313V
19:48:45 65.0'C 1200MHz 10000000000000001000 1.2313V

Paul Hutch
Posts: 369
Joined: Fri Aug 25, 2017 2:58 pm
Location: Blackstone River Valley, MA, USA
Contact: Website

Re: Voltage reduction under thermal throttling

Tue Apr 02, 2019 6:09 pm

I ran some some stress tests with a RasPi 3B+ with no heatsink and a sealed case, in an oven at 65°C ambient earlier this year to see how hot I could make it. I ran out of time and wasn't able to push it as far as I wanted but I did get it to throttle down to 600 MHz and the lowest I saw for a core voltage was 1.200V.

jdb
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 2032
Joined: Thu Jul 11, 2013 2:37 pm

Re: Voltage reduction under thermal throttling

Tue Apr 02, 2019 6:53 pm

There are three voltage/frequency setpoints for the 3B+
1.2V @ 600MHz - when idle or throttled due to 5V undervoltage or due to exceeding the 85C temp limit
"turbo" volts @ 1200MHz - when the temperature is above the soft temp limit and below the 85C temp limit. ARM frequency gets progressively ramped down to 600MHz between 80 and 85C.
"tubo+" volts @ 1400MHz - when the temperature is below the soft temp limit

The turbo/turbo+ volts are adjusted based on silicon characteristics, so tuned automatically on each individual board.
Rockets are loud.
https://astro-pi.org

jahboater
Posts: 4595
Joined: Wed Feb 04, 2015 6:38 pm

Re: Voltage reduction under thermal throttling

Wed Apr 03, 2019 1:13 pm

Paul Hutch wrote:
Tue Apr 02, 2019 6:09 pm
RasPi 3B+ with no heatsink and a sealed case, in an oven at 65°C ambient
Says a lot for the thermal management of the 3B+ that you need all that to get it to throttle!

Paul Hutch
Posts: 369
Joined: Fri Aug 25, 2017 2:58 pm
Location: Blackstone River Valley, MA, USA
Contact: Website

Re: Voltage reduction under thermal throttling

Wed Apr 03, 2019 2:51 pm

jdb wrote:
Tue Apr 02, 2019 6:53 pm
There are three voltage/frequency setpoints for the 3B+
<snipped excellent information>
Thank you for the info, one of the best things about this forum is how many RasPi engineers come to help us all out, keep up the good work. A big thanks to all of you, the rest of the RasPi staff, volunteer moderators, and regular contributors for making this place such a great resource.

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