micropython · kwagyeman · Aug 14, 2026 · Aug 14, 2026
diff --git a/ports/stm32/boards/OPENMV_N6/board.c b/ports/stm32/boards/OPENMV_N6/board.c
@@ -28,9 +28,10 @@
 #include "boardctrl.h"
 #include "xspi.h"
 
-// Values for OTP fuses for VDDIO2/3, to select low voltage mode (<2.5V).
+// Values for OTP fuses for VDDIO2/3/4, to select low voltage mode (<2.5V).
 // See RM0486, Section 5, Table 18.
 #define BSEC_HW_CONFIG_ID       (124U)
+#define BSEC_HWS_HSLV_VDDIO4    (1U << 14)
 #define BSEC_HWS_HSLV_VDDIO3    (1U << 15)
 #define BSEC_HWS_HSLV_VDDIO2    (1U << 16)
 
@@ -48,7 +49,7 @@ void mboot_board_early_init(void) {
     // Program high speed IO optimization fuses if they aren't already set.
     uint32_t fuse;
     BSEC_HandleTypeDef hbsec = { .Instance = BSEC };
-    const uint32_t mask = BSEC_HWS_HSLV_VDDIO2 | BSEC_HWS_HSLV_VDDIO3;
+    const uint32_t mask = BSEC_HWS_HSLV_VDDIO2 | BSEC_HWS_HSLV_VDDIO3 | BSEC_HWS_HSLV_VDDIO4;
     if (HAL_BSEC_OTP_Read(&hbsec, BSEC_HW_CONFIG_ID, &fuse) != HAL_OK) {
         fuse = 0;
     } else if ((fuse & mask) != mask) {

diff --git a/ports/stm32/boards/OPENMV_N6/mpconfigboard.h b/ports/stm32/boards/OPENMV_N6/mpconfigboard.h
@@ -101,9 +101,15 @@
 
 // SD Card SDMMC
 // SD_VSELECT: low(default)=3.3V IO, high=1.8V IO
-// SD_RESET: drive low to turn off SD VCC (pulled high by default)
+// SD_RESET: drive low to turn off SD VCC (pulled high by default on UHS-I capable
+//   hardware, in which case it reads high at startup; reads low otherwise)
 // SD_DETECT: pulled high in hardware, goes low when SD inserted
 #define MICROPY_HW_SDCARD_SDMMC             (1)
+#define MICROPY_HW_SDCARD_VSELECT_PIN       (pyb_pin_SD_VSELECT)
+#define MICROPY_HW_SDCARD_RESET_PIN         (pyb_pin_SD_RESET)
+// UHS-I SDR104 at 200MHz (the SDMMC kernel clock is HCLK at 200MHz).
+#define MICROPY_HW_SDCARD_UHS_SWITCH_PATTERN (SDMMC_SDR104_SWITCH_PATTERN)
+#define MICROPY_HW_SDCARD_UHS_CLK_DIV       (0)
 #define MICROPY_HW_SDCARD_CK                (pyb_pin_SD_SDIO_CK)
 #define MICROPY_HW_SDCARD_CMD               (pyb_pin_SD_SDIO_CMD)
 #define MICROPY_HW_SDCARD_D0                (pyb_pin_SD_SDIO_D0)

diff --git a/ports/stm32/boards/OPENMV_N6/stm32n6xx_hal_conf.h b/ports/stm32/boards/OPENMV_N6/stm32n6xx_hal_conf.h
@@ -13,6 +13,9 @@
 #define HSE_STARTUP_TIMEOUT (100)
 #define LSE_STARTUP_TIMEOUT (5000)
 
+// Enable the HAL's SD card 1.8V switch support, for UHS-I mode.
+#define USE_SD_TRANSCEIVER (1)
+
 #include "boards/stm32n6xx_hal_conf_base.h"
 
 #endif // MICROPY_INCLUDED_STM32N6XX_HAL_CONF_H
diff --git a/ports/stm32/boards/stm32n6xx_hal_conf_base.h b/ports/stm32/boards/stm32n6xx_hal_conf_base.h
@@ -97,7 +97,9 @@
 // Miscellaneous HAL settings
 #define VDD_VALUE           3300UL
 #define USE_RTOS            0
+#ifndef USE_SD_TRANSCEIVER
 #define USE_SD_TRANSCEIVER  0
+#endif
 #define USE_SPI_CRC         1
 
 // Disable dynamic callback registration