Thanks for your concern, There's the reason that I need to bypass the on board controller to get the highest update rate of display, I implemented my algorithm to drive the display and be able to get the faster and less display flicker via using almost 20MHz SPI clock with DMA feature. however it's only capable of generating the 1 bit color which is not what I wanted, I'm currently implementing the 3 MOSI SPI by using 3 SPI interface with DMA and push out each bit in sequence and making the clock signal longer to cover all 3 data bit coming out from each interface. but the harder (and confusing) part is to generate the GCP signal to control the tone of VFD. I'm currently looking to use the method that dynamically change the Timer frequency on the fly. anyway I want to hear some advice from you. Talking with engineering person would be appreciated. 

Hello, Recently I got the GU144X40-K610A8 display. It's really nice Graphic display and really fast update too. but recently I implemented the custom controller based on STM32 (SPI DMA at 18MHz connected directly to the display bypassing on board CPU for higher Framerate). The display is working just fine, however In the datasheet of the display (not the module) mentioned about GCP (Gradient Control pulse) and this VFD has 3 Serial data input. right now I got the idea for how to implement 3 Serial data output by using separate SPI bus (Mine has 3) and join the clock pin together then execute the DMA in sequentially and quickly.

but the problem is how exactly to control the GCP pin? 

Since its frequency keeps changing after the Blank pin goes low. and hardware Timer is fixed frequency (but can change the frequency on the fly).