Reading LCD-TFT peripheral registers in a stm32f769i-discovery

Question

I am creating a set of utilities for testing microcontroller software. One of these is a generic screenshooter. The idea behind it is to use the debugger (gdb) to access the LCD-TFT registers and use it to find, read and interpret the current framebuffer. However, all memory reads in the LCD-TFT region (0x40016800) return only zeros. I have used a simple test application which is able to display a simple image, so I know that the configuration of the LCD is correct. I have used the debugger to confirm that it is writing to the expected framebuffer address to the expected address (LTDC_L2CFBAR). I have also modified the application to read-back the framebuffer address written to the peripheral register, but the application code got back 0x0 as well. Are these registers generally not readable? Do I need some extra configuration to get these values?