ESP32 SD Card Directory Listing Performance

[Cybo57]

Hi, I have just upgraded from v1.0.4 to v2.0.2 and have seen a significant slowdown in the speed of listing files on an SD card.
Under v1.0.4 the listing speed appears to be limited by the serial interface speed, but under v2.0.2 the speed is down to 2 files/sec.

I am using exactly the same hardware for both tests, ESP32 dev board, with SPI connected MicroSD adapter. This issue can be seen using the standard SD_Test example.

Looking at the SPI traffic using a logic analyser:
- Under V1.0.4 there are only small gaps in the data stream ~1ms, probably due to the serial writes for the file details.
- Under v2.0.2 there is a (suspicious) 100ms gap between bursts of SPI activity, each file listing taking 5 bursts giving the 2 files/sec.

The SPI clock is 4MHz in both cases.

Any ideas what is causing this?