Decrease the totalDuration of RFAL software Library

[silae]

Hello,

I added the RFAL software library to my existing wireless charger project.

When I set totalDuration to 50U, there are cases where it cannot detect the card. I get better results when I set totalDuration to 25U. Will it cause problems if I reduce the value of the totalDuration parameter in the library for NFC/RFID card detection? What is range for totalDuration parameter? How should I adjust it?

[Ulysses HERNIOSUS]

Hi,

typical values of totalDuration are more in the 100ms to 500ms range. It denotes the desired polling period.

A full polling cycle with not tags found likely ends up in the 6 to 60ms range (depending how many technologies are enabled).

I presume with setting the totalDuration=25 you are ending up with pretty much constant field. This may indicate that there is an issue on the tag side which according to specifications needs to be powered and ready to respond after latest ~5ms.

BR, Ulysses

[silae]

Hello,

"A Power Transmitter with a separate NFC unit, as described in Section 3.2.1, Using a separate NFC
unit, should continuously poll for all tag technologies throughout all phases—even during power
transfer. The polling loop cycle time should be minimized for the fastest card/tag detection (e.g. less
than 50 ms)."

The relevant part of the Qi standard we are asked to follow with is as above.

What should we do to achieve the desired Qi standard above?

[Ulysses HERNIOSUS · Accepted solution]

Hi, 

for 50 vs 25ms differences in detection it could be that this is related to timings. If going more into this direction then we I would propose to analyze based on Logic Analyzer traces (SPI+IRQ).

For the purpose of performing card protection for Qi we are providing a module rfal_cd.c inside our rfal which performs necessary steps in a more condensed way than normal NFC Forum higher layer (rfal_nfc.c). It can be used in a blocking manner. If you delay by 5ms between two calls of rfalCdDetectCard() you should get close to a minimal timing. This module will also try to identify phones emulating NFC cards. A Qi charger can then charge the phone anyhow. If this discrimination is interesting for you we also have another enhancement (under NDA) to it which you need to request through your local ST support.

BR, Ulysses