libopencm3
A free/libre/open-source firmware library for various ARM Cortex-M3 microcontrollers.
STM32L4
Here is a list of all modules:
[detail level 1234]
 STM32L4xxLibraries for ST Microelectronics STM32L4xx series
 ADClibopencm3 STM32L4xx Analog to Digital Converters
 FLASHlibopencm3 STM32L4xx FLASH
 PWRlibopencm3 STM32L4xx Power Control
 RCClibopencm3 STM32L4xx Reset and Clock Control
 STM32L4xx DefinesDefined Constants and Types for the STM32L4xx series
 SYSCFG DefinesDefined Constants and Types for the STM32L4xx Sysconfig
 RTC DefinesDefined Constants and Types for the STM32L4xx RTC
 CRC DefinesDefined Constants and Types for the STM32L4xx CRC Generator
 DMA DefinesDefined Constants and Types for the STM32L4xx DMA Controller
 SPI DefinesDefined Constants and Types for the STM32L4xx SPI
 RCC DefinesDefined Constants and Types for the STM32L4xx Reset and Clock Control
 USART DefinesDefined Constants and Types for the STM32L4xx USART
 PWR DefinesDefined Constants and Types for the STM32L4xx Power Control
 FLASH DefinesDefined Constants and Types for the STM32L4xx Flash Control
 IWDG DefinesDefined Constants and Types for the STM32L4xx Independent Watchdog Timer
 ADC DefinesDefined Constants and Types for the STM32L4xx Analog to Digital Converter
 Timer Defineslibopencm3 Defined Constants and Types for the STM32L4xx Timers
 I2C DefinesDefined Constants and Types for the STM32L4xx I2C
 GPIO DefinesDefined Constants and Types for the STM32L4xx General Purpose I/O
 USART register base addressesHolds all the U(S)ART peripherals supported
 User interrupt service routines (ISR) prototypes for STM32 L4 series
 DebuggingMacros and functions to aid in debugging
 NVIC Defineslibopencm3 Cortex Nested Vectored Interrupt Controller
 User interrupts for STM32 L4 series
 Cortex M0/M3/M4 System InterruptsIRQ numbers -3 and -6 to -9 are reserved
 SysTick Defineslibopencm3 Defined Constants and Types for the Cortex SysTick
 Clock source selection
 CRS DefinesSTM32 Clock Recovery System: Defined Constants and Types
 USB DefinesDefined Constants and Types for the STM32F* USB drivers
 U(S)ART convenience FlagsWe define the "common" lower flag bits using a standard name, allowing them to be used regardless of which usart peripheral version you have
 USB DriversDefined Constants and Types for the USB Drivers
 USB Standard Structure DefinitionsDefined Constants and Types for the USB Standard Structure Definitions
 User interrupt service routines (ISR) defaults for STM32 L4 series
 NVIClibopencm3 Cortex Nested Vectored Interrupt Controller
 SysTicklibopencm3 Cortex System Tick Timer
 CRSlibopencm3 STM32 Clock Recovery Subsystem
 Generic USB DriversGeneric USB Drivers
 Generic USB Control RequestsGeneric USB Control Requests
 Generic USB Standard Request InterfaceGeneric USB Standard Request Interface
 Exti_defines
 Rng_fileThis library supports the random number generator peripheral (RNG) in the STM32F4 series of ARM Cortex Microcontrollers by ST Microelectronics
 CRC
 Dma_file
 Gpio_file
 I2c_file
 Iwdg_file
 Rtc_file
 Spi_file
 Timer_file
 Usart_file