diff --git a/core/embed/firmware/main.c b/core/embed/firmware/main.c
index b3d206d89d..304699f88c 100644
--- a/core/embed/firmware/main.c
+++ b/core/embed/firmware/main.c
@@ -300,6 +300,9 @@ void SVC_C_Handler(uint32_t *stack) {
       // raising privileges.
       stack[6] = (uintptr_t)reboot_to_bootloader;
       return;
+    case SVC_GET_SYSTICK_VAL: {
+      systick_val_copy = SysTick->VAL;
+    } break;
     default:
       stack[0] = 0xffffffff;
       break;
diff --git a/core/embed/trezorhal/common.h b/core/embed/trezorhal/common.h
index 1781ed4c85..d032a27318 100644
--- a/core/embed/trezorhal/common.h
+++ b/core/embed/trezorhal/common.h
@@ -76,6 +76,7 @@ void show_pin_too_many_screen(void);
 
 void hal_delay(uint32_t ms);
 uint32_t hal_ticks_ms();
+void hal_delay_us(uint16_t delay_us);
 
 void collect_hw_entropy(void);
 #define HW_ENTROPY_LEN (12 + 32)
diff --git a/core/embed/trezorhal/optiga/optiga_transport.c b/core/embed/trezorhal/optiga/optiga_transport.c
index 9a724f6ec5..5a827dfe9c 100644
--- a/core/embed/trezorhal/optiga/optiga_transport.c
+++ b/core/embed/trezorhal/optiga/optiga_transport.c
@@ -175,8 +175,10 @@ static optiga_result optiga_i2c_write(const uint8_t *data, uint16_t data_size) {
     }
     if (HAL_OK == i2c_transmit(OPTIGA_I2C_INSTANCE, OPTIGA_ADDRESS,
                                (uint8_t *)data, data_size, I2C_TIMEOUT)) {
+      hal_delay_us(1000);
       return OPTIGA_SUCCESS;
     }
+    hal_delay_us(1000);
   }
   return OPTIGA_ERR_I2C_WRITE;
 }
diff --git a/core/embed/trezorhal/stm32f4/common.c b/core/embed/trezorhal/stm32f4/common.c
index 3af562b941..427f10b0be 100644
--- a/core/embed/trezorhal/stm32f4/common.c
+++ b/core/embed/trezorhal/stm32f4/common.c
@@ -46,6 +46,8 @@
 #define COLOR_FATAL_ERROR COLOR_BLACK
 #endif
 
+uint32_t systick_val_copy = 0;
+
 // from util.s
 extern void shutdown_privileged(void);
 
@@ -154,6 +156,17 @@ void __assert_func(const char *file, int line, const char *func,
 
 void hal_delay(uint32_t ms) { HAL_Delay(ms); }
 uint32_t hal_ticks_ms() { return HAL_GetTick(); }
+void hal_delay_us(uint16_t delay_us) {
+  uint32_t val = svc_get_systick_val();
+  uint32_t t = hal_ticks_ms() * 1000 +
+               (((SystemCoreClock / 1000) - val) / (SystemCoreClock / 1000000));
+  uint32_t t2 = t;
+  do {
+    val = svc_get_systick_val();
+    t2 = hal_ticks_ms() * 1000 +
+         (((SystemCoreClock / 1000) - val) / (SystemCoreClock / 1000000));
+  } while ((t2 - t) < delay_us);
+}
 
 // reference RM0090 section 35.12.1 Figure 413
 #define USB_OTG_HS_DATA_FIFO_RAM (USB_OTG_HS_PERIPH_BASE + 0x20000U)
diff --git a/core/embed/trezorhal/stm32f4/i2c.c b/core/embed/trezorhal/stm32f4/i2c.c
index 65ce9076f5..ba65738c69 100644
--- a/core/embed/trezorhal/stm32f4/i2c.c
+++ b/core/embed/trezorhal/stm32f4/i2c.c
@@ -171,9 +171,19 @@ HAL_StatusTypeDef i2c_transmit(uint16_t idx, uint8_t addr, uint8_t *data,
                                uint16_t len, uint32_t timeout) {
   return HAL_I2C_Master_Transmit(&i2c_handle[idx], addr, data, len, timeout);
 }
+
 HAL_StatusTypeDef i2c_receive(uint16_t idx, uint8_t addr, uint8_t *data,
                               uint16_t len, uint32_t timeout) {
-  return HAL_I2C_Master_Receive(&i2c_handle[idx], addr, data, len, timeout);
+  HAL_StatusTypeDef ret =
+      HAL_I2C_Master_Receive(&i2c_handle[idx], addr, data, len, timeout);
+#ifdef USE_OPTIGA
+  if (idx == OPTIGA_I2C_INSTANCE) {
+    // apply GUARD_TIME as specified by the OPTIGA datasheet
+    // (only applies to the I2C bus to which the OPTIGA is connected)
+    hal_delay_us(50);
+  }
+#endif
+  return ret;
 }
 
 HAL_StatusTypeDef i2c_mem_write(uint16_t idx, uint8_t addr, uint16_t mem_addr,
diff --git a/core/embed/trezorhal/stm32f4/supervise.h b/core/embed/trezorhal/stm32f4/supervise.h
index 7d51530d69..27699c5c73 100644
--- a/core/embed/trezorhal/stm32f4/supervise.h
+++ b/core/embed/trezorhal/stm32f4/supervise.h
@@ -6,11 +6,15 @@
 #define SVC_SHUTDOWN 4
 #define SVC_REBOOT_TO_BOOTLOADER 5
 #define SVC_REBOOT_COPY_IMAGE_HEADER 6
+#define SVC_GET_SYSTICK_VAL 7
 
 #include <string.h>
 #include "common.h"
 #include "image.h"
 
+// from common.c
+extern uint32_t systick_val_copy;
+
 // from util.s
 extern void shutdown_privileged(void);
 extern void reboot_to_bootloader(void);
@@ -87,3 +91,13 @@ static inline void svc_reboot_copy_image_header(const uint8_t *image_address) {
     reboot_to_bootloader();
   }
 }
+
+static inline uint32_t svc_get_systick_val(void) {
+  if (is_mode_unprivileged() && !is_mode_handler()) {
+    __asm__ __volatile__("svc %0" ::"i"(SVC_GET_SYSTICK_VAL) : "memory");
+    return systick_val_copy;
+  } else {
+    systick_val_copy = SysTick->VAL;
+    return systick_val_copy;
+  }
+}