Teensy LC 8 & 16 MHz Options

[Phyixel]

So, after searching the forum & Google about running the LC at 8 MHz I couldn't find anything so I figured it must be easy to set the LC to run at lower speeds and it turns out that it is! (I think).

*EDIT Added 4 & 2 MHz, If you want these speeds add them to the teensy boards.txt.
All I did was a little copy-past job within the teensy boards.txt.

I simply added:

teensyLC.menu.speed.16=16 MHz (No USB)
teensyLC.menu.speed.8=8 MHz (No USB)
teensyLC.menu.speed.4=4 MHz (No USB)
teensyLC.menu.speed.2=2 MHz (No USB)

and:

teensyLC.menu.speed.16.build.fcpu=16000000
teensyLC.menu.speed.16.build.flags.optimize=-Os
teensyLC.menu.speed.16.build.flags.ldspecs=--specs=nano.specs
teensyLC.menu.speed.8.build.fcpu=8000000
teensyLC.menu.speed.8.build.flags.optimize=-Os
teensyLC.menu.speed.8.build.flags.ldspecs=--specs=nano.specs
teensyLC.menu.speed.4.build.fcpu=4000000
teensyLC.menu.speed.4.build.flags.optimize=-Os
teensyLC.menu.speed.4.build.flags.ldspecs=--specs=nano.specs
teensyLC.menu.speed.2.build.fcpu=2000000
teensyLC.menu.speed.2.build.flags.optimize=-Os
teensyLC.menu.speed.2.build.flags.ldspecs=--specs=nano.specs

I uploaded the blink sketch as a basic test and also took some current measurements using an separate UNO & a Adafruit INA219 DC current sensor and compared it to a Teensy 3.1 also running the blink sketch (tested at 24 MHz optimized and 8 MHz speeds):
*Edit Added 4 & 2 MHz tests

Teensy LC - No USB - Blink Sketch
2 MHz : LED off: 3 mA
2 MHz : LED on:  5 mA
---
4 MHz : LED off: 4 mA
4 MHz : LED on:  7 mA
---
8 MHz : LED off: 5 mA
8 MHz : LED on:  8 mA
---
24 MHz opt : LED off: 9 mA
24 MHz opt : LED on:  12 mA
---
Teensy 3.1 - No USB - Blink Sketch
8 MHz : LED off: 7 mA
8 MHz : LED on:  9 mA
---
24 MHz opt : LED off: 17 mA
24 MHz opt : LED on:  19 mA

I don't know if the setup above is the 'right' way to do it and why it was not just added to begin with but it seems to work OK, I'm using this LC in my clock project where every uA counts and have been running it for a few days now and its been running the same as when I was using a 3.1.

I hope these speeds can be added as and option in future teensyduino releases as I think its a good option for the Teensy LC in low power applications when clock speed helps the overall power use, as the LC uses less power than a 3.1.

 

[duff]

you should add 4MHz and 2MHz also. 2MHz goes into special low power state and should run at ~1mA if you don't need alot of processing power.

 

[PaulStoffregen]

I wonder if we can do 4 MHz on this chip in VLPR mode?

 

[duff]

I think I tested all them out but i'll try again and let you know.

 

[duff]

I wonder if we can do 4 MHz on this chip in VLPR mode?

I didn't read your question right, yes VLPR works at 4 MHz on Teensy3.x, I'll check out TeensyLC also, I'll have to dig up my notes since from what I remember its not same clock transitions than 2 MHz VLPR.

 

[PaulStoffregen]

Did we hit some sort of bug with the oscillator on Teensy 3.1?

The L-series chips have a lot of much more interesting low-power options, like running the serial ports and timers from a faster clock than the processor.

 

[duff]

Did we hit some sort of bug with the oscillator on Teensy 3.1?

It works, change the BUS/FLASH clock divider for 1 MHz and for core clock 4 MHz (BLPE) in VLPR. **edit.. plus change peripherals setups i.e uart

TeensyLC works at 4(BLPE) and 2(BLPI) MHz but it looks like it can't divide the clock down to 1 MHz max FLASH/BUS for VLPR at core clock at 4 MHz.

The L-series chips have a lot of much more interesting low-power options, like running the serial ports and timers from a faster clock than the processor.

Yes I see, running the TPM at 8 MHz seems interesting in VLPR. Looks like the uart, spi, adc, dac, tpm, i2s and dma might work in partial stop modes.