feat: state path to switch into standalone mode

src/main.c

@@ -1,11 +1,12 @@
 #include "registers/system/system.h"
 #include "states.h"
+#include "sdcard/sdcard.h"
 
 int main(void) {
 
     SYSTEM_Initialize();
 
-    state_t current_state = STATE_STANDBY;
+    state_t current_state = SDCARD_standalone_check() == SUCCESS ? STATE_STANDALONE : STATE_STANDBY;
 
     while (1) {
         current_state = STATES_RunState(current_state);

src/sdcard/sdcard.c

@@ -15,7 +15,9 @@
 #define FILENAME_SIZE (SFN_MAX + SFN_SUFFIX_LEN + 1)
 #define BUF_MAX FF_MIN_SS
 #define SDCARD_DRIVE "0:"
+#define CONFIG_FILENAME "PSLAB.CFG"
 
+static bool s_mounted = false;
 static TCHAR s_sector_buf[BUF_MAX];
 _Static_assert(
     sizeof(s_sector_buf) == 512,
@@ -141,3 +143,49 @@ response_t SDCARD_get_file_info(void)
 
     return SUCCESS;
 }
+
+/**
+ * @brief Read the configuration file from the SD card.
+ * @return true if the config file was read successfully, false otherwise or if the config structure is invalid.
+ */
+static bool read_config_file(void) {
+    FIL file;
+    if (f_open(&file, CONFIG_FILENAME, FA_READ) != FR_OK) {
+        return false;
+    }
+
+    TCHAR buf[6] = {0}; // Config file should have a magic header of 5 bytes
+    UINT bytes_read = 0;
+    if (f_read(&file, buf, sizeof buf - 1, &bytes_read) != FR_OK
+        || bytes_read != sizeof buf - 1) {
+        f_close(&file);
+        return false;
+    }
+    f_close(&file);
+
+    return (buf[0] == 'P' && buf[1] == 'S' && buf[2] == 'L' && buf[3] == 'A' && buf[4] == 'B');
+}
+
+void SDCARD_standalone_unmount(void) {
+    if (s_mounted) {
+        f_mount(0, SDCARD_DRIVE, 0);
+        s_mounted = false;
+    }
+}
+
+response_t SDCARD_standalone_check(void) {
+    if (!SD_SPI_IsMediaPresent()) {
+        return FAILED;
+    }
+
+    static FATFS drive;
+    if (f_mount(&drive, SDCARD_DRIVE, 1) != FR_OK) {
+        s_mounted = false;
+        return FAILED;
+    }
+    s_mounted = true;
+
+    bool ok = read_config_file();
+    SDCARD_standalone_unmount();
+    return ok ? SUCCESS : FAILED;
+}

src/sdcard/sdcard.h

@@ -97,4 +97,20 @@ response_t SDCARD_read_file(void);
  */
 response_t SDCARD_get_file_info(void);
 
+/**
+ * @brief Unmount SD-card after standalone configuration checks.
+ */
+void SDCARD_standalone_unmount(void);
+
+/**
+ * @brief Check if SD-card is present and can be mounted.
+ * 
+ * @details Checks if the SD-card can be mounted and if the configuration file is present and valid.
+ *          If the configuration file is not present or invalid, or if the SD-card is not mounted, the function returns FAILED.
+ *          The configuration file is expected to be named "PSLAB.CFG" and contain a magic header of 5 bytes with a null terminator.
+ * 
+ * @return SUCCESS
+ */
+response_t SDCARD_standalone_check(void);
+
 #endif // _SDCARD_H

src/states.c

@@ -36,9 +36,23 @@ state_t RunCommand(void) {
     return STATE_STANDBY;
 }
 
+/**
+ * @brief Run in standalone mode until serial traffic is detected.
+ * @return STATE_STANDALONE or STATE_RUNCOMMAND if serial traffic is detected.
+ */
+state_t Standalone(void) {
+    if (UART_IsRxReady(U1SELECT)) {
+        return STATE_RUNCOMMAND;
+    } 
+
+    WATCHDOG_TimerClear();
+    return STATE_STANDALONE;
+}
+
 state_func_t* const state_table[NUM_STATES] = {
     Standby,
     RunCommand,
+    Standalone,
 };
 
 state_t STATES_RunState(state_t current_state) {

src/states.h

@@ -16,6 +16,7 @@ extern "C" {
     typedef enum {
         STATE_STANDBY,
         STATE_RUNCOMMAND,
+        STATE_STANDALONE,
         NUM_STATES
     } state_t;