Register definitions

The file <cyg/hal/var_io.h> provides definitions related to AT91 subsystems. This file should not be included explicitly, but is included automatically whenever <cyg/hal/hal_io.h> is included. This file includes register definitions for the interrupt controller, power management controller, clock generator, memory controller, external bus interface, GPIO, USART, MCI, CAN, TWI (I²C®), Ethernet, timer counter, RTC, and SPI subsystems, depending on the exact model.