libraries/sd: Allow changing the default clock settings for the initialization and transfer states.

Author: oliviermartin

libraries/fs/sd/SDFileSystem.cpp

@@ -122,6 +122,10 @@
 SDFileSystem::SDFileSystem(PinName mosi, PinName miso, PinName sclk, PinName cs, const char* name) :
     FATFileSystem(name), _spi(mosi, miso, sclk), _cs(cs) {
     _cs = 1;
+
+    // Set default to 100kHz for initialisation and 1MHz for data transfer
+    _init_sck = 100000;
+    _transfer_sck = 1000000;
 }
 
 #define R1_IDLE_STATE           (1 << 0)
@@ -143,8 +147,8 @@ SDFileSystem::SDFileSystem(PinName mosi, PinName miso, PinName sclk, PinName cs,
 #define SDCARD_V2HC 3
 
 int SDFileSystem::initialise_card() {
-    // Set to 100kHz for initialisation, and clock card with cs = 1
-    _spi.frequency(100000);
+    // Set to SCK for initialisation, and clock card with cs = 1
+    _spi.frequency(_init_sck);
     _cs = 1;
     for (int i = 0; i < 16; i++) {
         _spi.write(0xFF);
@@ -209,8 +213,9 @@ int SDFileSystem::disk_initialize() {
         debug("Set 512-byte block timed out\n");
         return 1;
     }
-    
-    _spi.frequency(1000000); // Set to 1MHz for data transfer
+
+    // Set SCK for data transfer
+    _spi.frequency(_transfer_sck);
     return 0;
 }
 

libraries/fs/sd/SDFileSystem.h

@@ -73,7 +73,13 @@ class SDFileSystem : public FATFileSystem {
     int _write(const uint8_t *buffer, uint32_t length);
     uint64_t _sd_sectors();
     uint64_t _sectors;
-    
+
+    void set_init_sck(uint32_t sck) { _init_sck = sck; }
+    // Note: The highest SPI clock rate is 20 MHz for MMC and 25 MHz for SD
+    void set_transfer_sck(uint32_t sck) { _transfer_sck = sck; }
+    uint32_t _init_sck;
+    uint32_t _transfer_sck;
+
     SPI _spi;
     DigitalOut _cs;
     int cdv;