Why is this code so slow?

[lpcware]

Content originally posted in LPCWare by Dave3891 on Sun Jul 31 21:21:01 MST 2011
I have been trying different ideas to get 3 (6 in the future) variable frequency's generated with the 1343.

My best case is with match registers and interrupts.
But with just 3 (all on timer32 0) I can't get anything better then 125khz max.
I am looking to get around 350khz on 6 pins max, but nothing seems to get me close.

Each one has to be able to have a variable frequency/period and an adjustable on time. And right now I am testing worst case will all on at a high frequency.
Any idea's on the right way to do this or am I asking to much of this chip?

I have tried the highest optimization level as well.

Thanks
Dave

[lpcware]

Content originally posted in LPCWare by Ex-Zero on Wed Aug 03 02:32:25 MST 2011

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Quote:
...I will find out in a few days when I get the boards...

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Please keep me informed. Can't be wrong to think out of the box :)

[lpcware]

Content originally posted in LPCWare by Rob65 on Wed Aug 03 01:05:26 MST 2011
Could we get back to the lpc1xxx again?
This forum still is about LPCXpresso and not about STM or other Cortex chips ...

You need 6 PWM channels with a frequency (up to) 350 kHz if I remember correctly.
The question is if you really need diffent PWM frequencies.

The lpc17xx (I use the lpc1754) has one general PWM unit with 6 outputs that all share the same frequency (one timer with 6 match outputs) and a motor control PWM that contains 3 completely seperate PWM channels all with their own timer and match register.

So you can get up to 4 different frequencies.
And the general PWM unit can also be set such that 2 match registers are used to get 3 "double edge controller" PWM outputs. They still all share the same frequency but you are free to choose at which time each signal becomes high or low again.

Regards,

Rob

[lpcware]

Content originally posted in LPCWare by gbm on Wed Aug 03 00:32:39 MST 2011
Nuvoton M0 chips have up to 8 PWM channels wih independent cycle settings plus 4 toggle-capable timers. All of this at less than $1.5.

[lpcware]

Content originally posted in LPCWare by Dave3891 on Tue Aug 02 15:47:18 MST 2011

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Quote: qili
how many of those timers can be configured to have their own output pins?

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Looking at the 32 discovery board it looks like most of the timers have a pin.
There are about 18 pins with a timer association, but this was just a quick look.

[lpcware]

Content originally posted in LPCWare by qili on Tue Aug 02 04:46:13 MST 2011

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Quote: Dave3891

I might order a STM32 discovery... it has 12 timers.

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how many of those timers can be configured to have their own output pins?

[lpcware]

Content originally posted in LPCWare by acno on Tue Aug 02 01:50:43 MST 2011

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Quote: Dave3891
I wanted to use toggle mode with the match registers, but I could not think of a good compact code way to keep track of if the toggle is high or low.
And I need to be able to set the pulse to active high or active low depending on the application.

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The constraint is if you want indipendent control of active high or low on each channel. If all the channels are of the same polarities, I think that with a 'set on match' or 'clear on match' you should be able to do what you want and with a LPC17xx where you have a PWM timer with 6 channel and motor control PWM timer it should be finally possible.

I still not used the motor control PWM timer, but it is quite sophisticated and specifically designed to generate up to 6 complex PWM signals, that is basically your problem.


Andrea

[lpcware]

Content originally posted in LPCWare by Dave3891 on Mon Aug 01 17:02:50 MST 2011

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Quote: KTownsend
Don't worry ... I've heard he just gets his trainee to answer most of the questions now :D

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What does he do that he gets a trainee? Is he a embedded programmer for a profession?

[lpcware]

Content originally posted in LPCWare by ktownsend on Mon Aug 01 14:51:59 MST 2011

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Quote: Dave3891
Thanks for the help Zero, they should be paying you for all the questions you answer.

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Don't worry ... I've heard he just gets his trainee to answer most of the questions now :D

[lpcware]

Content originally posted in LPCWare by Dave3891 on Mon Aug 01 11:46:40 MST 2011
I ordered 2 of them with shipping for $27.70 so they are a good deal.

Looking in the reference manual it does look like I can use the general purpose timers to generate 6 individual PWM channels.

I will find out in a few days when I get the boards.

Dave

[lpcware]

Content originally posted in LPCWare by Ex-Zero on Mon Aug 01 11:21:09 MST 2011

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Quote: Dave3891
I might order a STM32 discovery... it has 12 timers.Dave

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Quote:

Up to 12 timers
[LIST]
[*]Up to three 16-bit timers, each with up to 4 IC/OC/PWM or pulse counter
[/LIST]
                
[LIST]
[*]16-bit, 6-channel advanced-control timer: up to 6 channels for PWM output, dead time generation and emergency stop
[/LIST]
                
[LIST]
[*]One 16-bit timer, with 2 IC/OC, 1 OCN/PWM, dead-time generation and emergency stop
[/LIST]
                
[LIST]
[*]Two 16-bit timers, each with IC/OC/OCN/PWM, dead-time generation and emergency stop
[/LIST]
                
[LIST]
[*]2 watchdog timers (Independent and Window)
[/LIST]
                
[LIST]
[*]SysTick timer: 24-bit downcounter
[/LIST]
                
[LIST]
[*]Two 16-bit basic timers to drive the DAC
[/LIST]

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Sorry, I'm not (yet) familiar with ST so I don't know if  it's possible to generate 6 independent timer :mad:

But it's worth a trial :)

[lpcware]

Content originally posted in LPCWare by Dave3891 on Mon Aug 01 10:12:55 MST 2011
I will need the 6 outputs, and it looks like PWM is the only fast way to go.

I might order a STM32 discovery... it has 12 timers.

Thanks for the help Zero, they should be paying you for all the questions you answer.


Dave

[lpcware]

Content originally posted in LPCWare by Ex-Zero on Mon Aug 01 09:58:45 MST 2011

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Quote: Dave3891
So even with PWM the 1343 and 1769 only have 4 timers...

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1769 has an additional PWM and RIT and therefore the possibility to add a calculated  output :)

So it's a fundamental question if you need (or want to use) a 1769 :confused:

[lpcware]

Content originally posted in LPCWare by Dave3891 on Mon Aug 01 09:44:13 MST 2011
So even with PWM the 1343 and 1769 only have 4 timers... so I am not going to get 6 indipendent output then ...
Back to the drawing board. Mabey a CPLD generator attached to the 1343.

Thanks
Dave

[lpcware]

Content originally posted in LPCWare by Ex-Zero on Mon Aug 01 09:02:32 MST 2011

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Quote:

...I am looking to get around 350khz on 6 pins max, but nothing seems to get me close...

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Just measured your Interrupt: 2.3 µs for 3 pins, and that's your problem :mad:

With 6 pins you're ending below 100kHz :eek:

I think your only chance is to use PWM. Unfortunately you need one timer per PWM, so 4 independent timer should be no problem.

Your basic idea to calculate new MR values costs a lot of time (and then you don't use Match outputs :eek:).

Overall I would say it's hopeless to expand your code even to 4 fast pins :mad:

[lpcware]

Content originally posted in LPCWare by Dave3891 on Mon Aug 01 08:45:28 MST 2011
I wanted to use toggle mode with the match registers, but I could not think of a good compact code way to keep track of if the toggle is high or low.
And I need to be able to set the pulse to active high or active low depending on the application.

[lpcware]

Content originally posted in LPCWare by Dave3891 on Mon Aug 01 08:28:52 MST 2011

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Quote:
Did you try to reduce your Prescale Register ?

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I have reduced the match register, but anything lower and it misses interrupts.

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Quote:
At 50MHz of bus this means only 200 cycles. What is the CPU clock ?

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I am running at 72mhz. I am using the Embedded Artists LPC1343.


Thanks
Dave

[lpcware]

Content originally posted in LPCWare by acno on Mon Aug 01 06:01:26 MST 2011

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Quote: Dave3891
I have been trying different ideas to get 3 (6 in the future) variable frequency's generated with the 1343.

My best case is with match registers and interrupts.
But with just 3 (all on timer32 0) I can't get anything better then 125khz max.
I am looking to get around 350khz on 6 pins max, but nothing seems to get me close.

Each one has to be able to have a variable frequency/period and an adjustable on time. And right now I am testing worst case will all on at a high frequency.
Any idea's on the right way to do this or am I asking to much of this chip?

I have tried the highest optimization level as well.

Thanks
Dave

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Well, with that code You have 2 IRQ per cycle, so at 125kHz the cpu has only 4us (8/2) for executing the ISR. At 50MHz of bus this means only 200 cycles. What is the CPU clock ?
You can also check how much time the cpu spend in the ISR, trace it with a GPIO port for example.
Also, I will try to use directly the timer match outputs, with them the ISR routine should need much less code.

Andrea

[lpcware]

Content originally posted in LPCWare by Ex-Zero on Mon Aug 01 00:18:33 MST 2011
Did you try to reduce your Prescale Register ?