ESP8266SdFat Performance vs Upstream SdFat

[forkineye]

Basic Infos

• This issue complies with the issue POLICY doc.
• I have read the documentation at readthedocs and the issue is not addressed there.
• I have tested that the issue is present in current master branch (aka latest git).
• I have searched the issue tracker for a similar issue.
• If there is a stack dump, I have decoded it.
• I have filled out all fields below.

Platform

• Hardware: Wemos D1 mini (ESP-12)
• Core Version: 2.7.4 - 2843a5a
• Development Env: Arduino IDE
• Operating System: Windows

Settings in IDE

• Module: Generic ESP8266 Module
• Flash Mode: dio
• Flash Size: 4MB
• lwip Variant: v2 Lower Memory
• Reset Method: nodemcu
• Flash Frequency: 40Mhz
• CPU Frequency: 160MHz
• Upload Using: SERIAL
• Upload Speed: 921600

Problem Description

SPI SD card usage utilizing SD or SDFS is much slower than expected. Testing utilizing the ESP8266SdFat->bench example sketch is showing write speeds of ~130 KB/s and read speeds of ~650 KB/s. Attempts to utilize ENABLE_EXTENDED_TRANSFER_CLASS and SdFatEx in the bench example fail to compile. Analysis with a logic analyzer show many pauses in SPI transactions while writing data. While troubleshooting, I decided to replace ESP8266SdFat with the upstream version which now supports ESP8266 and ESP32. Testing with the upstream SdFat->bench example showed write speeds of ~1.6MB/s and read speeds of 3.2MB/s, much faster than the current version included in ESP8266SdFat. This does seem to break the SD/SDFS wrappers due to changes in SdFat. Usage of ENABLE_DEDICATED_SPI in SdFat didn't cause any noticeable increase of performance which may warrant further analysis.

MCVE Sketch

2.7.4 ESP8266SdFat bench.ino
Upstream SdFat bench.ino