CH341_CLKRATE
#define CH341_MIN_RATE(ps) (CH341_CLKRATE / (CH341_CLK_DIV((ps), 1) * 512))
#define CH341_MIN_BPS DIV_ROUND_UP(CH341_CLKRATE, CH341_CLK_DIV(0, 0) * 256)
#define CH341_MAX_BPS (CH341_CLKRATE / (CH341_CLK_DIV(3, 0) * 2))
div = CH341_CLKRATE / (clk_div * speed);
if (16 * CH341_CLKRATE / (clk_div * div) - 16 * speed >=
16 * speed - 16 * CH341_CLKRATE / (clk_div * (div + 1)))