LPC MicrocontrollersのトピックRe: CTIMER - reading count value while count changes

CTIMER - reading count value while count changes

klausrenner — Wed, 11 Jul 2018 13:48:08 GMT

I'm using a CTIMER0 in counter mode to count external pulses. Do I need to worry about the count changing while I'm reading the counter register? Is there a way to use a shadow register? I'm using an LPC54606 and don't see any mention of this in the user manual.

Re: CTIMER - reading count value while count changes

victorjimenez — Wed, 11 Jul 2018 19:16:13 GMT

Hello Klaus Renner,

You don't need to worry, you won't have any problem while reading this register.

The shadow register is for a completely different purpose. The Match Shadow registers contain the values that the corresponding Match Registers are (optionally) reloaded with at the start of each new counter cycle.

Hope it helps!

Victor.

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Re: CTIMER - reading count value while count changes

klausrenner — Wed, 11 Jul 2018 19:43:06 GMT

Thanks, but just to be clear, let me restate my question.

Is there protection in hardware that prevents the counter register from

changing while the firmware reads its value?

Since my external counter clock is varying and not related to any clock on

chip I worry about occasionally getting bad readings.

I currently ensure that this can't happen by using a capture register. I

trigger the capture by changing the state of a port pin when my firmware

needs the counter value. That port pin is externally wired to the capture

input in order to force the capture, then my firmware reads the capture

it ties up two port pins and adds some extra code. If it's not necessary

I'd rather not do it, but I do need to be sure that the counter reading is

never garbled, and it would take some time to prove...

*Klaus Renner | Cooper Perkins, Inc. | **10 Maguire Road, Bldg. 4 |

Lexington, MA 02421*

desk: 781-761-4807 | http://www.cooperperkins.com

This email message contains confidential information.

On Wed, Jul 11, 2018 at 3:17 PM, victorjimenez <admin@community.nxp.com>

Re: CTIMER - reading count value while count changes

victorjimenez — Fri, 13 Jul 2018 17:53:50 GMT

Hello Klaus Renner,

Is there protection in hardware that prevents the counter register from changing while the firmware reads its value?

No, there isn't a hardware protection that prevents this, but you don't need one. You can read the value of the counter anytime without getting wrong values, doesn't matter if the timer is running or on hold.

If the timer is still running when you want to read the value of the counter then you will read the last value stored in the buffer of the timer. So, even if the value changes while you are reading it you won't get an incorrect value. Why do you think you may get bad readings occasionally?

Hope it helps!

Victor.