Hello,
the BT81x can only display ASTC compressed images directly from flash and 1024x600 is too large for RAM_G, at least in full color, so you need to convert the images to ASTC first.
In my example code I am using EVE_cmd_flashupdate() to write an flash image with an UTF-8 font from RAM_G to the external flash. This flash image is zlib compressed which in case of the example has two reasons, the first is that the .glyph files are highly compressable due to a combination of redundant structures since every glyh is one image and depending on the font there are a number of empty glyphs.
The second reason is that CMD_INFLATE only works with correct data, so the data also gets verified.
I have a function EVE_memWrite_sram_buffer() as means of transferring data from the host to EVE.
So first you just loop thru reading the data from sd-card to a buffer and writing that buffer to RAM_G in EVE.
And then you call EVE_cmd_flashupdate() to write that data from RAM_G to the flash.
Noteworthy is that CMD_FLASHREAD only accepts data in multiples of 4096.
And it helps to have the binary blob already in place that is needed by EVE to initialise the flash to full speed.
Annother consideration is that the ASTC format needs to be fixed.
On the one side to make the flash-layout planable, on the other side to display it correctly.
I usually go with 8x8 which is 2 bits per pixel, so a 1024x600 image would come out as 150k compressed.
Note, table 12 in the programming guide is partly wrong:
https://en.wikipedia.org/wiki/Adaptive_scalable_texture_compression