I am interested on drawing in the LCD screen using direct writes in the framebuffer (no emWin, TouchGFX libraries whatsoever, just using MCUXpresso and fsl_lcdc driver. The project is based on the SDK demo project lpcxpresso54608_demo_apps_touch_cursor
I want to draw graphics with a greater color depth. For example, 24 bits per pixel. In order to do this, I need to allocate a bigger frame buffer, which does not fit in the internal RAM of the LPC54608. Therefore I want to allocate the frame buffer on the external SDRAM on the eval board. Can I have any example code for this?
So far, I tried using a macro declaration to allocate the buffer variable on the RAM4 region (which corresponds to the external RAM):
__attribute__(( section(".data.$RAM4"), aligned(8) ))
static uint8_t s_frameBufs[IMG_HEIGHT][IMG_WIDTH];
In addition to that, I added the functions necessary to bring up the external SDRAM from the example lpcxpresso54608_driver_examples_emc_sdram:
My project builds correctly and the compiler statistics show indeed the variable is stored in the external RAM:
Memory region Used Size Region Size %age Used
PROGRAM_FLASH: 92532 B 512 KB 17.65%
BOARD_FLASH: 0 GB 16 MB 0.00%
SRAM_0_1_2_3: 8576 B 160 KB 5.23%
SRAMX: 0 GB 32 KB 0.00%
USB_RAM: 0 GB 8 KB 0.00%
BOARD_SDRAM: 65280 B 16 MB 0.39%
Finished building target: lpcxpresso54608_demo_apps_touch_cursor.axf
However, it does not run after programming, the display on the eval board is completely white and, shockingly: The debugger hangs, it gives communication error and the board must be power cycled.
I think this application could be useful in many cases, an I am looking forward to know if there’s any example or application note explaining how to put the frame buffer on the external SDRAM.