Configuring LTDC with TrustZone enabled

[antonello-one]

Hello,

I'm trying to write an application with TrustZone enabled that uses the LTDC peripheral.

My application:

• boots into secure world
• configures the LTDC peripheral and its interrupt, as well as the relevant GPIO pins, as non-secure
• switches to the non-secure world.

In the non-secure world, I configure the LTDC, passing a buffer placed in non-secure SRAM and start drawing. However, the screen stays black.

I'm able to access the LTDC registers from the non-secure world, so it seems that the permission settings for the MCU are correct. My guess is that for some reason the LTDC peripheral itself does not have permission to access the SRAM, am I missing some other settings?

[Ch_JE]

Hello ,

Try to configure the TrustZone Security Controller (TZSC) for a specific peripheral (in your case, the LTDC).

(Through HAL GTZC driver)

• Secure and non-secure attributes can only be configured from the secure state.
• Security and privilege attributes can be set independently.
• By default, access is non-secure and unprivileged.

Regards

[antonello-one]

Hello,

Thanks for your response. I've already configured the GTZC, I have applied the following configuration:

Set the LTDC peripheral as non-secure:

if (HAL_GTZC_TZSC_ConfigPeriphAttributes(GTZC_PERIPH_LTDCUSB, GTZC_TZSC_PERIPH_NSEC | GTZC_TZSC_PERIPH_NPRIV) != HAL_OK) {
  Error_Handler();
}

Set the LTDC global interrupt and LTDC global error interrupt as non-secure by configuring the NVIC->ITNS register:

#define NVIC_INIT_ITNS4_VAL      0x00001FFF

#if defined (NVIC_INIT_ITNS4) && (NVIC_INIT_ITNS4 == 1U)
  NVIC->ITNS[4] = NVIC_INIT_ITNS4_VAL;
#endif

Set the GPIOs used by the LTDC as non-secure:

/*IO attributes management functions */
  HAL_GPIO_ConfigPinAttributes(GPIOE, GPIO_PIN_2|GPIO_PIN_3|LCD_ON_Pin|TP_IRQ_Pin
                          |BL_CTRL_Pin|GPIO_PIN_7|GPIO_PIN_8|GPIO_PIN_9
                          |GPIO_PIN_10|GPIO_PIN_11|GPIO_PIN_12|GPIO_PIN_13
                          |GPIO_PIN_14|GPIO_PIN_15|GPIO_PIN_0, GPIO_PIN_NSEC);

  /*IO attributes management functions */
  HAL_GPIO_ConfigPinAttributes(GPIOF, GPIO_PIN_0|GPIO_PIN_1|GPIO_PIN_2, GPIO_PIN_NSEC);

  /*IO attributes management functions */
  HAL_GPIO_ConfigPinAttributes(GPIOC, GPIO_PIN_0|GPIO_PIN_1|GPIO_PIN_6|GPIO_PIN_7
                          |GPIO_PIN_8|GPIO_PIN_9|GPIO_PIN_10|GPIO_PIN_11
                          |GPIO_PIN_12, GPIO_PIN_NSEC);

  /*IO attributes management functions */
  HAL_GPIO_ConfigPinAttributes(GPIOA, GPIO_PIN_1|GPIO_PIN_3|USB_FAULT_Pin|GPIO_PIN_9
                          |GPIO_PIN_10|GPIO_PIN_11|GPIO_PIN_12, GPIO_PIN_NSEC);

  /*IO attributes management functions */
  HAL_GPIO_ConfigPinAttributes(GPIOB, GPIO_PIN_1|GPIO_PIN_2|GPIO_PIN_13|GPIO_PIN_15
                          |GPIO_PIN_9, GPIO_PIN_NSEC);

  /*IO attributes management functions */
  HAL_GPIO_ConfigPinAttributes(GPIOD, GPIO_PIN_8|GPIO_PIN_9|GPIO_PIN_10|GPIO_PIN_11
                          |GPIO_PIN_12|GPIO_PIN_13|GPIO_PIN_14|GPIO_PIN_15
                          |GPIO_PIN_0|GPIO_PIN_1|RED_LED_Pin|GPIO_PIN_3
                          |GREEN_LED_Pin|GPIO_PIN_6, GPIO_PIN_NSEC);

  /*IO attributes management functions */
  HAL_GPIO_ConfigPinAttributes(GPIOH, GPIO_PIN_9|GPIO_PIN_10|GPIO_PIN_11|GPIO_PIN_12
                          |GPIO_PIN_13|GPIO_PIN_14|GPIO_PIN_15, GPIO_PIN_NSEC);

  /*IO attributes management functions */
  HAL_GPIO_ConfigPinAttributes(GPIOI, GPIO_PIN_0|GPIO_PIN_1|GPIO_PIN_2|GPIO_PIN_3, GPIO_PIN_NSEC);

  /*IO attributes management functions */
  HAL_GPIO_ConfigPinAttributes(GPIOG, GPIO_PIN_9|GPIO_PIN_10|GPIO_PIN_15, GPIO_PIN_NSEC);

Maybe I misconfigured something or I need some other device?

Thanks