diff --git a/fusee/fusee-primary/src/lib/fatfs/diskio.c b/fusee/fusee-primary/src/lib/fatfs/diskio.c
index 096ff4863..9de072b9e 100644
--- a/fusee/fusee-primary/src/lib/fatfs/diskio.c
+++ b/fusee/fusee-primary/src/lib/fatfs/diskio.c
@@ -15,6 +15,13 @@
 
 static bool g_ahb_redirect_enabled = false;
 
+// Only use voltage switching in stage2 and later.
+#ifdef FUSEE_STAGE1_SRC
+#define MMC_VOLTAGE_SWITCHING_ALLOWED false
+#else
+#define MMC_VOLTAGE_SWITCHING_ALLOWED true
+#endif
+
 /* Global sd struct. */
 static struct mmc g_sd_mmc = {0};
 static bool g_sd_initialized = false;
@@ -26,7 +33,7 @@ int initialize_sd_mmc(void) {
 	}
 
 	if (!g_sd_initialized) {
-		int rc = sdmmc_init(&g_sd_mmc, SWITCH_MICROSD);
+		int rc = sdmmc_init(&g_sd_mmc, SWITCH_MICROSD, MMC_VOLTAGE_SWITCHING_ALLOWED);
 		if (rc == 0) {
 			g_sd_initialized = true;
 			return 0;
diff --git a/fusee/fusee-primary/src/sdmmc.c b/fusee/fusee-primary/src/sdmmc.c
index 905958495..64034cf45 100644
--- a/fusee/fusee-primary/src/sdmmc.c
+++ b/fusee/fusee-primary/src/sdmmc.c
@@ -140,7 +140,7 @@ enum sdmmc_clock_dividers {
     MMC_CLOCK_DIVIDER_SDR12  = 31, // 16.5, from the TRM table
     MMC_CLOCK_DIVIDER_SDR25  = 15, // 8.5, from the table
     MMC_CLOCK_DIVIDER_SDR50  = 7,  // 4.5, from the table
-    MMC_CLOCK_DIVIDER_SDR104 = 2,  // 2, from the datasheet
+    MMC_CLOCK_DIVIDER_SDR104 = 4,  // 2, from the datasheet
 
     /* Clock dividers: MMC */
     MMC_CLOCK_DIVIDER_HS26   = 30, // 16, from the TRM table
@@ -568,11 +568,11 @@ struct PACKED sdmmc_function_status {
 
     /* support for various speed modes */
     uint16_t group1_support_reserved1  : 8;
-    uint16_t ddr50_support   :  1;
-    uint16_t sdr104_support  :  1;
-    uint16_t sdr50_support   :  1;
-    uint16_t sdr25_support   :  1;
     uint16_t sdr12_support   :  1;
+    uint16_t sdr25_support   :  1;
+    uint16_t sdr50_support   :  1;
+    uint16_t sdr104_support  :  1;
+    uint16_t ddr50_support   :  1;
     uint16_t group1_support_reserved2  : 3;
 
 
@@ -631,10 +631,14 @@ static const uint16_t sdmmc_bounce_dma_boundary = MMC_DMA_BOUNDARY_8K;
  * Sets the current SDMMC debugging loglevel.
  *
  * @param loglevel Current log level. A higher value prints more logs.
+ * @return The loglevel prior to when this was applied, for easy restoration.
  */
-void sdmmc_set_loglevel(int loglevel)
+int sdmmc_set_loglevel(int loglevel)
 {
+    int original_loglevel = sdmmc_loglevel;
     sdmmc_loglevel = loglevel;
+
+    return original_loglevel;
 }
 
 
@@ -887,9 +891,9 @@ static int sdmmc1_enable_supplies(struct mmc *mmc)
     pinmux->dmic3_clk  =  PINMUX_SELECT_FUNCTION0;
     gpio_configure_mode(GPIO_MICROSD_SUPPLY_ENABLE, GPIO_MODE_GPIO);
     gpio_configure_direction(GPIO_MICROSD_SUPPLY_ENABLE, GPIO_DIRECTION_OUTPUT);
+
+    // Bring up the SD card fixed regulator.
     gpio_write(GPIO_MICROSD_SUPPLY_ENABLE, GPIO_LEVEL_HIGH);
-
-
     return 0;
 }
 
@@ -1415,6 +1419,7 @@ static int sdmmc_apply_clock_speed(struct mmc *mmc, enum sdmmc_bus_speed speed,
         mmc_print(mmc, "TODO: double the data rate here!");
     }
 
+
     // Re-enable the clock, if necessary.
     if (enable_after) {
         sdmmc_clock_enable(mmc, true);
@@ -2902,13 +2907,17 @@ static int sdmmc_mmc_wait_for_card_readiness(struct mmc *mmc)
     int rc;
     uint32_t response[4];
 
+
     while (true) {
 
         uint32_t response_masked;
 
         // Ask the SD card to identify its state. It will respond with readiness and a capacity magic.
+        int original_loglevel = sdmmc_set_loglevel(0);
         rc = sdmmc_send_command(mmc, CMD_SEND_OPERATING_CONDITIONS, MMC_RESPONSE_LEN48,
                 MMC_CHECKS_NONE, 0x40000080, response, 0, false, false, NULL);
+        sdmmc_set_loglevel(original_loglevel);
+
         if (rc) {
             mmc_print(mmc, "ERROR: could not read the card's operating conditions!");
             return rc;
@@ -2953,8 +2962,10 @@ static int sdmmc_sd_wait_for_card_readiness(struct mmc *mmc, uint32_t *response)
     while (true) {
 
         // Ask the SD card to identify its state.
+        int original_loglevel = sdmmc_set_loglevel(0);
         rc = sdmmc_send_simple_app_command(mmc, CMD_APP_SEND_OP_COND,
                 MMC_RESPONSE_LEN48, MMC_CHECKS_NONE, argument, response);
+        sdmmc_set_loglevel(original_loglevel);
         if (rc) {
             mmc_print(mmc, "ERROR: could not read the card's operating conditions!");
             return rc;
@@ -3071,7 +3082,7 @@ static int sdmmc_sd_card_init(struct mmc *mmc)
     mmc->uses_block_addressing = !!(ocr & MMC_SD_OPERATING_COND_HIGH_CAPACITY);
 
     // If the card supports using 1V8, drop down using lower voltages.
-    if (ocr & MMC_SD_OPERATING_COND_ACCEPTS_1V8) {
+    if (mmc->allow_voltage_switching && ocr & MMC_SD_OPERATING_COND_ACCEPTS_1V8) {
         if (mmc->operating_voltage != MMC_VOLTAGE_1V8) {
             rc = mmc->switch_to_low_voltage(mmc);
             if (rc)
@@ -3369,14 +3380,18 @@ static int sdmmc_initialize_defaults(struct mmc *mmc)
  * @param mmc The SDMMC structure to be initiailized with the device state.
  * @param controler The controller description to be used; usually SWITCH_EMMC
  *      or SWITCH_MICROSD.
+ * @param allow_voltage_switching True if we should allow voltage switching,
+ *      which may not make sense if we're about to chainload to another component,
+ *      a la fusee stage1.
  */
-int sdmmc_init(struct mmc *mmc, enum sdmmc_controller controller)
+int sdmmc_init(struct mmc *mmc, enum sdmmc_controller controller, bool allow_voltage_switching)
 {
     int rc;
 
     // Get a reference to the registers for the relevant SDMMC controller.
     mmc->controller = controller;
     mmc->regs = sdmmc_get_regs(controller);
+    mmc->allow_voltage_switching = false;
 
     // Set the defaults for the card, including the default function pointers
     // for the assumed card type, and the per-controller options.
diff --git a/fusee/fusee-primary/src/sdmmc.h b/fusee/fusee-primary/src/sdmmc.h
index 25e8cf1e4..67952b401 100644
--- a/fusee/fusee-primary/src/sdmmc.h
+++ b/fusee/fusee-primary/src/sdmmc.h
@@ -150,6 +150,7 @@ struct mmc {
     /* Controller properties */
     const char *name;
     bool use_dma;
+    bool allow_voltage_switching;
     unsigned int timeout;
     enum tegra_named_gpio card_detect_gpio;
     enum sdmmc_write_permission write_enable;
@@ -221,17 +222,22 @@ enum sdmmc_partition {
  * Sets the current SDMMC debugging loglevel.
  *
  * @param loglevel Current log level. A higher value prints more logs.
+ * @return The loglevel prior to when this was applied, for easy restoration.
  */
-void sdmmc_set_loglevel(int loglevel);
+int sdmmc_set_loglevel(int loglevel);
 
 
 /**
- * Initiailzes an SDMMC controller for use with an eMMC or SD card device.
+ * Set up a new SDMMC driver.
  *
- * @param mmc An (uninitialized) structure for the MMC device.
- * @param controller The controller number to be initialized. Either SWITCH_MICROSD or SWITCH_EMMC.
+ * @param mmc The SDMMC structure to be initiailized with the device state.
+ * @param controler The controller description to be used; usually SWITCH_EMMC
+ *      or SWITCH_MICROSD.
+ * @param allow_voltage_switching True if we should allow voltage switching,
+ *      which may not make sense if we're about to chainload to another component,
+ *      a la fusee stage1.
  */
-int sdmmc_init(struct mmc *mmc, enum sdmmc_controller controller);
+int sdmmc_init(struct mmc *mmc, enum sdmmc_controller controller, bool allow_voltage_switching);
 
 
 /**