STM32F4_RCC_PLLCFGR
base + STM32F4_RCC_PLLCFGR, 22, 1, 0,
pllm = readl(base + STM32F4_RCC_PLLCFGR) & 0x3f;
{ "vco", STM32F4_RCC_PLLCFGR, 24, 25 },