with IAR 6.30, and SPITX register is always 0x00000000, and the IRQ work
This may not show an issue. When you write to the SPITX register in master
mode, you are loading the FIFO.
The contents of the FIFO are then moved to a bi-shift register and clocked out
of the part.
Once the byte has been transmitted, the FIFO will be empty and the SPITX
register will return to a default value.
Do you see the correct value clocked on the MOSI pin? Are the 8x clocks visible
on a scope?