SD card: initial shoehorning of SD code, part 1.

Part 1 is, implement

 - M20: List SD card.
 - M21: Initialize SD card (has to be done before listing).
 - M22: Release SD card.

Do all this in one chunk, splitting this up wouldn't allow to test
the result.

gcode_process.c

@@ -26,6 +26,8 @@
 #include	"clock.h"
 #include	"config_wrapper.h"
 #include	"home.h"
+#include "sd.h"
+
 
 /// the current tool
 uint8_t tool;
@@ -374,6 +376,30 @@ void process_gcode_command() {
 				tool = next_tool;
 				break;
 
+      #ifdef SD
+      case 20:
+        //? --- M20: list SD card. ---
+        sd_list("/");
+        break;
+
+      case 21:
+        //? --- M21: initialise SD card. ---
+        //?
+        //? Has to be done before doing any other operation, including M20.
+        sd_mount();
+        break;
+
+      case 22:
+        //? --- M22: release SD card. ---
+        //?
+        //? Not mandatory. Just removing the card is fine, but results in
+        //? odd behaviour when trying to read from the card anyways. M22
+        //? makes also sure SD card printing is disabled, even with the card
+        //? inserted.
+        sd_unmount();
+        break;
+      #endif /* SD */
+
 			case 82:
 				//? --- M82 - Set E codes absolute ---
 				//?

pff_conf.h

@@ -11,7 +11,7 @@
 /---------------------------------------------------------------------------*/
 
 #define _USE_READ   1   /* Enable pf_read() function */
-#define _USE_DIR    0   /* Enable pf_opendir() and pf_readdir() function */
+#define _USE_DIR    1   /* Enable pf_opendir() and pf_readdir() function */
 #define _USE_LSEEK  0   /* Enable pf_lseek() function */
 #define _USE_WRITE  0   /* Enable pf_write() function */
 

sd.c

@@ -6,10 +6,67 @@
 
 #ifdef SD
 
+#include "delay.h"
+#include "serial.h"
+#include "sersendf.h"
 
+
+static FATFS sdfile;
+static FRESULT result;
+
+/** Initialize SPI for SD card reading.
+*/
 void sd_init(void) {
   WRITE(SD_CARD_SELECT_PIN, 1);
   SET_OUTPUT(SD_CARD_SELECT_PIN);
 }
 
+/** Mount the SD card.
+*/
+void sd_mount(void) {
+  result = pf_mount(&sdfile);
+  if (result != FR_OK)
+    sersendf_P(PSTR("E: SD init failed. (%su)"), result);
+}
+
+/** Unmount the SD card.
+
+  This makes just sure subsequent reads to the card do nothing, instead of
+  trying and failing. Not mandatory, just removing the card is fine, as well
+  as inserting and mounting another one without previous unmounting.
+*/
+void sd_unmount(void) {
+  pf_unmount(&sdfile);
+}
+
+/** List a given directory.
+
+  \param path The path to list. Toplevel path is "/".
+
+  A slash is added to directory names, to make it easier for users to
+  recognize them.
+*/
+void sd_list(const char* path) {
+  FILINFO fno;
+  DIR dir;
+
+  serial_writechar('\n');
+  result = pf_opendir(&dir, path);
+  if (result == FR_OK) {
+    for (;;) {
+      result = pf_readdir(&dir, &fno);
+      if (result != FR_OK || fno.fname[0] == 0)
+        break;
+      serial_writestr((uint8_t *)fno.fname);
+      if (fno.fattrib & AM_DIR)
+        serial_writechar('/');
+      serial_writechar('\n');
+      delay_ms(2); // Time for sending the characters.
+    }
+  }
+  else {
+    sersendf_P(PSTR("E: failed to open dir. (%su)"), result);
+  }
+}
+
 #endif /* SD */

sd.h

@@ -17,6 +17,12 @@
 
 void sd_init(void);
 
+void sd_mount(void);
+
+void sd_unmount(void);
+
+void sd_list(const char* path);
+
 #endif /* SD_CARD_SELECT_PIN */
 
 #endif /* _SD_H */