Here are the data structures with brief descriptions:

C_epstate
C_ueintx
Cavr_adc_mux_t
Cavr_adc_t
Cavr_bitbang_t	SPI Module initialization and state structure
Cavr_cycle_timer_pool_t	Timer pool contains a pool of timer slots available, they all start queued into the 'free' qeueue, are migrated to the 'active' queue when needed and are re-queued to the free one when done
Cavr_cycle_timer_slot_t	Each timer instance contains the absolute cycle number they are hoping to run at, a function pointer to call and a parameter
Cavr_eeprom_desc_t
Cavr_eeprom_t
Cavr_extint_t	This module is just a "relay" for the pin change IRQ in the IO port module
Cavr_flash_t	Handles self-programming subsystem if the core supports it
Cavr_gdb_t
Cavr_gdb_watchpoints_t
Cavr_int_table_t	Interrupt vectors, and their enable/clear registers
Cavr_int_vector_t	Interrupt vector for the IO modules
Cavr_io_t	IO module base struct Modules uses that as their first member in their own struct
Cavr_io_usb
Cavr_iopin_t	Pin structure
Cavr_ioport_external_t	Ioctl used to set default port state when set as input
Cavr_ioport_getirq_t	This ioctl takes a avr_regbit_t, compares the register address to PORT/PIN/DDR and return the corresponding IRQ(s) if it matches
Cavr_ioport_state_t	Ioctl used to get a port state
Cavr_ioport_t	Definition for an IO port
Cavr_irq_hook_t
Cavr_irq_pool_t	IRQ Pool structure
Cavr_irq_t	Public IRQ structure
Cavr_kind_t	Static constructor for each of the AVR devices
Cavr_lin_t
Cavr_regbit_t	This 'structure' is a packed representation of an IO register 'bit' (or consecutive bits)
Cavr_spi_t
Cavr_symbol_t	Symbol loaded from the .elf file
Cavr_t	Main AVR instance
Cavr_timer_comp_t
Cavr_timer_t
Cavr_timer_wgm_t
Cavr_trace_data_t	This is only ever used if CONFIG_SIMAVR_TRACE is defined
Cavr_twi_msg_irq_t
Cavr_twi_msg_t
Cavr_twi_t
Cavr_uart_t
Cavr_usb_t
Cavr_vcd_log_t
Cavr_vcd_signal_t	This structure registers IRQ change hooks to various "source" IRQs and dumps their values (if changed) at certain intervals into the VCD file
Cavr_vcd_t
Cavr_watchdog_t
Celf_firmware_t
Cihex_chunk_t	A .hex file chunk (base address + size)
Cmcu_t
Cusb_internal_state