Filling in cyg_flash_devtab[] array

no this should be enough... are you sure that your custom driver is included in the eCos configuration? Could there be a# ifdef somewhere that prevents those macros from running?

An easy way I have to find out if a specific part of the source code is compiled, is to voluntarily introduce a syntax error just before of after those macros. If you can still compile eCos without any errors, then it means that your code isn't compiled, or ignored.

AFAIK the CYG_FLASH_DRIVER inserts an element statically in the code, during compile time, so there is no reason why the table wouldn't be populated.

Are you looking at the correct table? From what I'm seeing, the table used by those macros is cyg_flashdev, not cyg_flash_devtab