topic Re: Improving deep-sleep performance on the LPC1114 in LPCXpresso IDE

Improving deep-sleep performance on the LPC1114

lpcware — Thu, 16 Jun 2016 00:10:41 GMT

Content originally posted in LPCWare by ktownsend on Tue Feb 23 17:08:49 MST 2010
I've been testing out a prototype design with an LPC1114 + 868MHz transceiver, and since low-power is the main reason I opted for the 1114, I was a bit disappointed with the results in deep sleep mode. I'm sure that there is significant room for improvement in the SW, but I was wondering if anyone else has been working with the sleep modes to be able to give some tips on getting the power consumption as low as possible in SW (the HW is obviously another issue entirely).

For the entire board, I'm using around 4.4mA at 12MHz, and when I go into deep-sleep mode it drops to around 1.9mA, shutting off the following peripherals:

pmuSleep(pmuSleepMode_DeepSleep, 
  SCB_PDSLEEPCFG_SYSPLL_PD |
  SCB_PDSLEEPCFG_WDTOSC_PD |
  SCB_PDSLEEPCFG_ADC_PD |
  SCB_PDSLEEPCFG_BOD_PD);

I want to use a timer to raise an interrupt every 15 minutes, for example, to wake the device up to check for messages, and then go back into deep sleep. Does anyone have any suggestions about configuring this to get the power consumption as low as possible without having to go into power down mode (which is nice at <0.1mA, but fairly limited in that it can only be woken up with the WAKEUP pin).

I've been testing a number of combinations, but if someone can suggest a solid starting point for a common scenario like this it would save me some grunt work.

Re: Improving deep-sleep performance on the LPC1114

lpcware — Thu, 16 Jun 2016 00:10:42 GMT

Content originally posted in LPCWare by igorsk on Tue Feb 23 18:04:50 MST 2010
Maybe try also powering down the flash.
"In addition, the flash may be powered down in Deep-sleep mode resulting in savings in static leakage power - however at the expense of longer wake-up times for the flash memory."
BTW, where is this function from?

[B]Edit[/B]: okay, found the source, but posting code like that is not very useful when we can't see the implementation.

Re: Improving deep-sleep performance on the LPC1114

lpcware — Thu, 16 Jun 2016 00:10:43 GMT

Content originally posted in LPCWare by ktownsend on Tue Feb 23 18:44:33 MST 2010

Quote: igorsk
[B]Edit[/B]: okay, found the source, but posting code like that is not very useful when we can't see the implementation.

Sorry ... it was just to give an indication of the bits being set. I should have just listed the peripherals by name. I'm just playing around with different settings now, comparing the IRC to the external crystal, etc. The internal oscillator is less accurate, but since 12MHz is probably fast enough in this case it probably allows me to shut more peripheral blocks off and should cause that many problems. I left the flash on simply because I was worried it would slow down the wakeup process, but I should probably test it out rather than just running on assumptions.

Re: Improving deep-sleep performance on the LPC1114

lpcware — Thu, 16 Jun 2016 00:10:44 GMT

Content originally posted in LPCWare by igorsk on Tue Feb 23 19:08:33 MST 2010
The manual says:

Quote:
The flash power-up sequence for waking up from Deep-sleep mode takes 100 μs. Note that the flash does not need to be initialized in this case. If the flash is powered down, the user must wait for this time period before resuming flash operations. The power-up sequence after reset takes slightly longer to allow for the flash to initialize.

I'm not sure what exactly "the user must wait" mean... you can't execute instructions from powered down flash anyway, so it should happen automatically, right?
Unless they mean when you're executing from RAM?

Re: Improving deep-sleep performance on the LPC1114

lpcware — Thu, 16 Jun 2016 00:10:44 GMT

Content originally posted in LPCWare by ktownsend on Tue Feb 23 20:18:25 MST 2010
I didn't find the manual terribly clear on that either.

I think I'm going to put another board together without the LPC1114 just to get a rough idea of how much power the other components on the board are consuming ... should at least help me determine the real difference between sleep/deepsleep/powerdown in terms of power consumption.

Given that the 1114 is really aiming for the low power market, it would be nice to see some sort of app note on sleep and deepsleep, along with some simple examples of handling the wake on a timer interrupt, etc. It's rather time consuming trying to put together little pieces of information from ARM/NXP/etc. to get the whole picture.

Kevin.

Re: Improving deep-sleep performance on the LPC1114

lpcware — Thu, 16 Jun 2016 00:10:45 GMT

Content originally posted in LPCWare by rkiryanov on Wed Feb 24 00:14:03 MST 2010

Quote: KTownsend
Does anyone have any suggestions about configuring this to get the power consumption as low as possible

Turn off all unused peripherals, set the lowest possible frequency (kHz), configure all unused pins as "GPIO, out, no hysteresis, low" and sleep. Also, welcome to Power consumption tuning on Cortex-M0 :)

Re: Improving deep-sleep performance on the LPC1114

lpcware — Thu, 16 Jun 2016 00:10:45 GMT

Content originally posted in LPCWare by ktownsend on Thu Feb 25 16:40:00 MST 2010
I was able to get down to [B]0.49mA[/B] in deep sleep mode by paying a bit more attention to the datasheet (compared to 1.47mA previously). There are several bits that are 'reserved' but apparently still need to be set to a certain state during deep sleep mode, as follows (see PDSLEEPCFG in the UM):

For the 1114: bit 9 to 0, and bits 11+12 to 1
For the 1343: bit 9 and 11 to 1

This shaved off a full 1mA of power consumption. It slipped past me since I hadn't added a define to my system header file, given that the bits are reserved and I didn't think to add them in.

0.49mA still feels a bit high to me, but it's definately reasonable and I will do some tests powering down the flash as well to see how much power I can save and how long it takes to begin execution after wakeup, etc. Deep sleep is a lot more useful than power down since you can still exit with a simple interrupt.

Re: Improving deep-sleep performance on the LPC1114

lpcware — Thu, 16 Jun 2016 00:10:46 GMT

Content originally posted in LPCWare by rkiryanov on Thu Feb 25 22:31:35 MST 2010

Quote: KTownsend
0.49mA

If it is very sad. I haven't a board still, but I was hoping for 5-50 uA in sleep mode (not deep sleep) at 30kHz. 500uA is unacceptable. Can you upload your code?

Re: Improving deep-sleep performance on the LPC1114

lpcware — Thu, 16 Jun 2016 00:10:47 GMT

Content originally posted in LPCWare by ktownsend on Fri Feb 26 00:37:47 MST 2010

Quote: rkiryanov
If it is very sad. I haven't a board still, but I was hoping for 5-50 uA in sleep mode (not deep sleep) at 30kHz. 500uA is unacceptable. Can you upload your code?

That's indeed still high ... too high for my own needs ... but I'm sure I can get it lower with mix of HW and SW. It's always a slow, iterative process to get the power as low as possible. I still haven't tried all of the SW combinations (I'm kind of shooting in the dark since it's a new chip), and afterwards I need to look at the HW. When I say .49mA, I'm talking about the current consumed by the entire board (my own ... not the LPCXpresso) including an AT86RF212 radio transceiver in sleep mode, with all of the supporting HW that goes with it.

50uA in sleep mode is unrealistic, though. The user manual states 2mA in sleep mode at 12MHz (versus 3mA normally) ... though 6µA in deep sleep sounds great. I didn't even bother looking much at sleep mode because of that. Power-down mode isn't that useful to me either ... it's more appropriate for designing peripherals that are controlled by an external device.

Kevin.

Re: Improving deep-sleep performance on the LPC1114

lpcware — Thu, 16 Jun 2016 00:10:48 GMT

Content originally posted in LPCWare by rkiryanov on Fri Feb 26 00:45:07 MST 2010

Quote: KTownsend
the entire board

Probably, this is the problem. I will receive board next week and check it on my desk.

Quote: KTownsend
The user manual states 2mA in sleep mode at 12MHz (versus 3mA normally) ...

Try [B]KHz[/B] - watchdog oscillator (400KHz) with divider 10 to 20.

Re: Improving deep-sleep performance on the LPC1114

lpcware — Thu, 16 Jun 2016 00:10:48 GMT

Content originally posted in LPCWare by ktownsend on Fri Feb 26 01:04:46 MST 2010
I've got it down to 0.28mA turning off pretty much everything, though I need to do some SW test to determine the consequences of that. On the board I have the following:

MCP130T: ~45µA
ADP121: ~30µA
AT86RF212: <1µA (sleep)

I used 10µF ceramic caps instead of tantalums, etc., to save power, and was careful with discrete selection, but that means that at .28mA, minus external components, the LPC1114 and remaining components is using around 0.2mA in deep sleep at present, and I suspect there is still room for improvement ... I just need to do a lot of testing to shave off that last little bit. I think I can eventually get the total board to around 0.1mA though, which should be alright for me. I was planning on running at ~240:1 duty cycle, waking up maybe 5s every 20 minutes. At those power rates I can easily run from a small solar cell with a 2.5V supercapacitor (the board is design for 1.8V) forever ... no battery needed.

That said ... it would have been nice to have more information on getting the most from the deep sleep mode, and some examples from NXP or an app note. It's been a lot of trial and error, and I've had to make some decisions where I wasn't 100% clear on the consequences.

This is what I'm using at present:

    // Enter deep sleep mode
    pmuDeepSleep(SCB_PDSLEEPCFG_IRCOUT_PD |
                 SCB_PDSLEEPCFG_IRC_PD |
                 SCB_PDSLEEPCFG_FLASH_PD |
                 SCB_PDSLEEPCFG_BOD_PD |
                 SCB_PDSLEEPCFG_ADC_PD |
                 SCB_PDSLEEPCFG_WDTOSC_PD |
                 SCB_PDSLEEPCFG_SYSPLL_PD);
 
...
void pmuDeepSleep(U32 sleepCtrl)
{
  SCB_PDAWAKECFG = SCB_PDRUNCFG;
  // Datasheet indicates bits 11 and 12 must also be set to 1 for DS
  // and that bit 9 must be set to 0
  sleepCtrl &= ~(1 << 9);               // 9  = MAIN_REGUL_PD
  sleepCtrl |= (1 << 11) | (1 << 12);   // 12 = LP_REGUL_PD, 11 = ???
  SCB_PDSLEEPCFG = sleepCtrl;
  SCB_SCR |= SCB_SCR_SLEEPDEEP;
  __asm volatile ("WFI");
  return;
}

Re: Improving deep-sleep performance on the LPC1114

lpcware — Thu, 16 Jun 2016 00:10:49 GMT

Content originally posted in LPCWare by rkiryanov on Fri Feb 26 01:12:16 MST 2010

Quote: KTownsend
This is what I'm using at present:

Did you configured unused pins as GPIO, out, low? Floating pins can consume some current. Also, is it possible to wake up with timer from deep sleep?

Re: Improving deep-sleep performance on the LPC1114

lpcware — Thu, 16 Jun 2016 00:10:50 GMT

Content originally posted in LPCWare by ktownsend on Fri Feb 26 01:19:08 MST 2010

Quote: rkiryanov
Did you configured unused pins as GPIO, out, low? Floating pins can consume some current.

I have to go through it pin by pin to determine which pins I need to be in which state, and then explicitly set the rest, but there are definately a few µA that can be shaved off with that. Up until now I've been trying to make the code as generic as possible, so didn't get into configuring things pin by pin for this particular project.

I find it kind of annoying that the internal pull-up resistors are all enabled by default, though, since it adds more code and a potential problem for people who don't pay enough attention to the UM. I understand the idea behind the decision ... but they are trying to compensate for bad SW design in HW, and just making things more work in the long run. I've been wondering as well ... do the internal pull ups ONLY affect GPIO? If I'm using a pin as SPI, for example, do I still need to clear the internal resistor ... or is that only necessary when the pin multiplexing is set to GPIO?

Re: Improving deep-sleep performance on the LPC1114

lpcware — Thu, 16 Jun 2016 00:10:51 GMT

Content originally posted in LPCWare by rkiryanov on Fri Feb 26 01:22:12 MST 2010

Quote: KTownsend
do I still need to clear the internal resistor ...

On LPC2000 pull up/pull down works with SPI.

Re: Improving deep-sleep performance on the LPC1114

lpcware — Thu, 16 Jun 2016 00:10:52 GMT

Content originally posted in LPCWare by ktownsend on Fri Feb 26 01:25:03 MST 2010

Quote: rkiryanov
Also, is it possible to wake up with timer from deep sleep?

Sorry ... I missed that last part. I haven't yet gotten around to testing the wakeup code. Obviously you can't use a HW debugger for that, so I've been putting it off just trying to get the deep sleep consumption as low as possible. When I said I wasn't sure of the consequences of shutting certain things off, etc., thats what I meant ... I need to play around with it and see what's possible for wakeup, etc., and how long it takes. I'll probably start working on that tommorow. There are a number of issues I'll need to deal with the the RTOS level as well going into and coming out of deep sleep.

Re: Improving deep-sleep performance on the LPC1114

lpcware — Thu, 16 Jun 2016 00:10:52 GMT

Content originally posted in LPCWare by ktownsend on Fri Feb 26 01:27:38 MST 2010

Quote: rkiryanov
On LPC2000 pull up/pull down works with SPI.

Just as a precaution, I've been disabling the internal resistor on any pin I used. I wish this would have been the default state, though. The internal resistors are very useful and are a good way to reduce the total BOM count (and this required surface area) ... but it's troublesome to add one more potential problem by making them almost all default to enabled and pulled high, just to compensate for people writing bad code and not controlling their pin states properly.

Re: Improving deep-sleep performance on the LPC1114

lpcware — Thu, 16 Jun 2016 00:10:53 GMT

Content originally posted in LPCWare by rkiryanov on Fri Feb 26 01:57:51 MST 2010
How do you plan to start from 12MHz IRC to deep sleep? LPC1114 will draw all energy from supercap on morning.

Re: Improving deep-sleep performance on the LPC1114

lpcware — Thu, 16 Jun 2016 00:10:54 GMT

Content originally posted in LPCWare by ktownsend on Fri Feb 26 02:17:02 MST 2010

Quote: rkiryanov
How do you plan to start from 12MHz IRC to deep sleep? LPC1114 will draw all energy from supercap on morning.

I need to modify the code to switch to the IRC first, as the UM suggests ... I'm just comparing different settings to get an idea of how much power each peripheral is consuming. I've already put together some code to handle all of this, I've just been busy trying to get a sense of which peripherals should be left on and which should be disabled, etc.

As for the supercap, I think a large enough one should be more than enough for a couple days power combined with an efficient solar cell. Something like a 25F cap can make it through more than a day without sunlight. If I can get to around 100µA total in deep sleep, I'll only be consuming ~.166mAh with a 240:1 duty cycle.

With a 25F supercap on a 1.8V system, I should have 81 joules (E = 1.8² * 25 = 81). 81 joules / 1.8V = 45A; 45 / 3600 seconds = 0.0125Ah (or 12.5mAh).

Those are ideal figures, but if a 25F supercap on a 1.8V system will give me 12.5mAh, that should be enough to power my system for ~75 hours. If we don't have any sun during 75 hours we'll have far bigger problems than my little embedded device. :-)

That said ... it's all theoretical. I need to test this all out with a real board and see if it really works out. But even if it only performs half as well, that should still be sufficient, and having a battery-less system definately has a lot of advantages.

Here's a blog post I put together a while back thinking about this: http://www.microbuilder.eu/blog/09-11-13/Using_Supercapacitors_as_a_Power_Source.aspx

Re: Improving deep-sleep performance on the LPC1114

lpcware — Thu, 16 Jun 2016 00:10:55 GMT

Content originally posted in LPCWare by rkiryanov on Fri Feb 26 02:26:10 MST 2010
You calculations are wrong. Backup time calculted as

T = C * (U_charge - U_cutoff - I * R_supercap) / (I + I_leakage)

And 25F is the super cool supercap.

Re: Improving deep-sleep performance on the LPC1114

lpcware — Thu, 16 Jun 2016 00:10:55 GMT

Content originally posted in LPCWare by ktownsend on Fri Feb 26 03:06:29 MST 2010

Quote: rkiryanov
And 25F is the super cool supercap.

Just don't lick it when it's fully charged or your tongue will probably explode :p

It looks interesting on paper, but it's something I'll have to test out in practice to see how it really works out. I'm worried about the life of the supercap as well and temperature, amongst other things. A 1.8V system with a 2.5V supercap is still cutting it closer than I'd like for something capable of exploding, but you have other problems putting two supercaps in series to get above 2.5V, like ensuring equal charging, etc. It's next on the ToDo list, though. I've designed the sensor nodes in a way that the power cell is independent of the node anyway ... if the supercap/solar combination doesn't work, I can easily go to a LIPO or NIMH battery as well, though that has it's own problems. I really need to get <100µA first, though, in deep sleep, and work out all the details with the wakeup.