Function write_command 

pub fn write_command(word: u32)

Push a drawing or VRAM command word, or one of its parameters, to the GPU’s command port (GP0). Pairs with the word builders in psx_hw::gpu::gp0: write_command(gp0::draw_mode(...)).

With the present-queue feature, the word goes into the open command recording instead, if there is one, and an armed direct-access guard runs before the port write.