SRAM Memory Mirror

[malcolmmackay]

I'd like to transfer a large NDEF record (a few hundred bytes) using the 64 byte SRAM buffer to an Android phone. I do not intend to write an Android app, so I have ruled out pass through mode. Can I write this record to a phone in 64 byte chunks by using the memory Mirror feature?

I'm thinking of using Field Detect to trigger my MCU to write the next 64 bytes to SRAM, then set up the EEPROM address to mirror it to and enable SRAM_MIRROR_ON_OFF. This process repeats for each 64 byte section of the NDEF record. 

Will the Android phone wait for the MCU to write into SRAM without timing out? Is this how the memory Mirror feature was intended to be used? Has anyone tested something similar with the NT3H2211? 

[driesmoors]

Hi,

You should have a few milliseconds at your disposal after detecting the NFC field and before the Android phone starts reading the NFC memory. If you are too late, the phone will read rubbish or whatever is made available. There is no way for the Android phone to know when the data is available. AFAIK, there is no timing specification in the NFC specifications for this: it just assumes that when it starts reading - whenever that may be - the data is available.

The default Android behavior, when no APP is registered to the NDEF message of that MIME type, is to try and parse the data and show a display with a textual interpretation of the NDEF contents. In that case, the NFC memory will only be read once. To fetch the next 64 bytes (without an APP), you will need to physically remove the NTAG from the NFC field and bring it back again.

Best,