Notes

ARM EMBEDDED SYSTEMS

ANDREW N. SLOSS, ... CHRIS WRIGHT, in ARM System Developer's Guide, 2004

1.3.4 PERIPHERALS
Embedded systems that interact with the outside world need some form of peripheral device. A peripheral device performs input and output functions for the chip by connecting to other devices or sensors that are off-chip. Each peripheral device usually performs a single function and may reside on-chip. Peripherals range from a simple serial communication device to a more complex 802.11 wireless device.

All ARM peripherals are memory mapped—the programming interface is a set of memory-addressed registers. The address of these registers is an offset from a specific peripheral base address.

Controllers are specialized peripherals that implement higher levels of functionality within an embedded system. Two important types of controllers are memory controllers and interrupt controllers.

1.3.4.1 Memory Controllers
Memory controllers connect different types of memory to the processor bus. On power-up a memory controller is configured in hardware to allow certain memory devices to be active. These memory devices allow the initialization code to be executed. https://adomaintools.com/memory-controller/ must be set up by software; for example, when using DRAM, you first have to set up the memory timings and refresh rate before it can be accessed.

1.3.4.2 Interrupt Controllers
When a peripheral or device requires attention, it raises an interrupt to the processor. An interrupt controller provides a programmable governing policy that allows software to determine which peripheral or device can interrupt the processor at any specific time by setting the appropriate bits in the interrupt controller registers.

There are two types of interrupt controller available for the ARM processor: the standard interrupt controller and the vector interrupt controller (VIC).

The standard interrupt controller sends an interrupt signal to the processor core when an external device requests servicing. It can be programmed to ignore or mask an individual device or set of devices. The interrupt handler determines which device requires servicing by reading a device bitmap register in the interrupt controller.

The VIC is more powerful than the standard interrupt controller because it prioritizes interrupts and simplifies the determination of which device caused the interrupt. After associating a priority and a handler address with each interrupt, the VIC only asserts an interrupt signal to the core if the priority of a new interrupt is higher than the currently executing interrupt handler. Depending on its type, the VIC will either call the standard interrupt exception handler, which can load the address of the handler for the device from the VIC, or cause the core to jump to the handler for the device directly.
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