ESP32 Forum

Hello all,

Does anyone have any metrics for the maximum number of Access Points you can scan? I am scanning in wifi congested areas and I am running into issues with reliable repetitive scanning. I estimate that there may be over 150 WAP's in the local vicinity. Looking through the code, I see that memory is dynamically allocated to hold the scan results. Scanning usually works for me, but every once in a while I get the following error message:

08:21:04.864 CORRUPT HEAP: Bad head at 0x3ffe611c. Expected 0xabba1234 got 0x3ffe80e4
08:21:04.869 assertion "head != NULL" failed: file "/Users/ficeto/Desktop/ESP32/ESP32/esp‑idf‑public/components/heap/./multi_heap_poisoning.c", line 199, function: multi_heap_free
08:21:04.886 abort() was called at PC 0x40122b8f on core 0
08:21:04.892
08:21:04.892 Backtrace: 0x4008af50:0x3ffdcf30 0x4008b04f:0x3ffdcf50 0x40122b8f:0x3ffdcf70 0x4008ac61:0x3ffdcfa0 0x40083faa:0x3ffdcfc0 0x400872fd:0x3ffdcfe0 0x4000bec7:0x3ffdd000 0x401581c6:0x3ffdd020 0x40150b10:0x3ffdd040 0x40152e0f:0x3ffdd080 0x40187b2e:0x3ffdd0a0
08:21:04.918
08:21:04.918 Rebooting...

I am trying to either cap the number of WAP's that get scanned before giving up, or to try to increase the amount of memory available for the scan. I am currently running in ESP32-Arduino at the moment. Any thoughts?

Thanks!

Must you be in station mode to do this?
In promiscuous mode, there is a call back for wifi packets. Here you can do an infinite number of AP (as you would get a call back on each beacon frame).

Hi Hassan,

Thank you for the reply and the hint on the promiscuous mode. It's a more in-depth change for what I'm doing now, but it looks like that may work well. Any other memory issue might be in the ESP32-Arduino framework so I'm digging there as well.

I'm also looking for an answer regarding what dictates how many wifi's (RSSI and MAC addresses) are return by the scan?

While I'm at it, I'd also like to know what are the controls we have for scans, e.g. Can I have ESP32 scan a specified length
of time for maximum return APs or fast scans?

If I'm not getting all the wifi's that are found, then can I control so that I get all of the strongest RSSI?

Thanks