From 93f10609f4784fbe5a1580021553c1fa4a72dcc7 Mon Sep 17 00:00:00 2001
From: "Serguei S. Dukachev" <github@dukess.ru>
Date: Fri, 1 Oct 2021 15:48:20 +0300
Subject: [PATCH] SDMMC frequency selection based on board type (#5688)

* SDMMC frequency selection based on board type

On Olimex ESP32 EVB I/O operations with SD card can cause error when LAN is used in same time.
Problem is disappearing if SD MMC frequency lower down from SDMMC_FREQ_HIGHSPEED to SDMMC_FREQ_DEFAULT.

No problem if WiFi used instead LAN.

* Code rewritten according to https://github.com/espressif/arduino-esp32/pull/5688#pullrequestreview-759359645
---
 libraries/SD_MMC/src/SD_MMC.cpp   | 4 ++--
 libraries/SD_MMC/src/SD_MMC.h     | 9 ++++++++-
 variants/esp32-evb/pins_arduino.h | 1 +
 3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/libraries/SD_MMC/src/SD_MMC.cpp b/libraries/SD_MMC/src/SD_MMC.cpp
index 0c95fb9d..450657cf 100644
--- a/libraries/SD_MMC/src/SD_MMC.cpp
+++ b/libraries/SD_MMC/src/SD_MMC.cpp
@@ -36,7 +36,7 @@ SDMMCFS::SDMMCFS(FSImplPtr impl)
     : FS(impl), _card(NULL)
 {}
 
-bool SDMMCFS::begin(const char * mountpoint, bool mode1bit, bool format_if_mount_failed)
+bool SDMMCFS::begin(const char * mountpoint, bool mode1bit, bool format_if_mount_failed, int sdmmc_frequency)
 {
     if(_card) {
         return true;
@@ -46,7 +46,7 @@ bool SDMMCFS::begin(const char * mountpoint, bool mode1bit, bool format_if_mount
     sdmmc_host_t host;
     host.flags = SDMMC_HOST_FLAG_4BIT;
     host.slot = SDMMC_HOST_SLOT_1;
-    host.max_freq_khz = SDMMC_FREQ_HIGHSPEED;
+    host.max_freq_khz = sdmmc_frequency;
     host.io_voltage = 3.3f;
     host.init = &sdmmc_host_init;
     host.set_bus_width = &sdmmc_host_set_bus_width;
diff --git a/libraries/SD_MMC/src/SD_MMC.h b/libraries/SD_MMC/src/SD_MMC.h
index 6e40fd45..e8540b32 100644
--- a/libraries/SD_MMC/src/SD_MMC.h
+++ b/libraries/SD_MMC/src/SD_MMC.h
@@ -21,6 +21,13 @@
 #include "driver/sdmmc_types.h"
 #include "sd_defines.h"
 
+// If reading/writing to the SD card is unstable, 
+// you can define BOARD_MAX_SDMMC_FREQ with lower value (Ex. SDMMC_FREQ_DEFAULT) 
+// in pins_arduino.h for your board variant.
+#ifndef BOARD_MAX_SDMMC_FREQ
+#define BOARD_MAX_SDMMC_FREQ SDMMC_FREQ_HIGHSPEED
+#endif
+
 namespace fs
 {
 
@@ -31,7 +38,7 @@ protected:
 
 public:
     SDMMCFS(FSImplPtr impl);
-    bool begin(const char * mountpoint="/sdcard", bool mode1bit=false, bool format_if_mount_failed=false);
+    bool begin(const char * mountpoint="/sdcard", bool mode1bit=false, bool format_if_mount_failed=false, int sdmmc_frequency=BOARD_MAX_SDMMC_FREQ);
     void end();
     sdcard_type_t cardType();
     uint64_t cardSize();
diff --git a/variants/esp32-evb/pins_arduino.h b/variants/esp32-evb/pins_arduino.h
index 15fa98e2..a2e02dc7 100644
--- a/variants/esp32-evb/pins_arduino.h
+++ b/variants/esp32-evb/pins_arduino.h
@@ -29,5 +29,6 @@ static const uint8_t MISO  = 15;
 static const uint8_t SCK   = 14;
 
 #define BOARD_HAS_1BIT_SDMMC
+#define BOARD_MAX_SDMMC_FREQ SDMMC_FREQ_DEFAULT
 
 #endif /* Pins_Arduino_h */