![]() ![]() (And aren't even inside the core running your instructions. Peripherals, including those on the same SoC as the CPU's, are a different matter though: I/O registers are not at all the same thing because they're not also accessible via register-numbers as operands for instructions other than load or store. ![]() So a memory address may refer to either a portion of physical RAM. A memory-mapped register is something which you access through an address or a pointer (in languages that has pointers). Specifically for ARM, the ARM architecture does not have memory-mapped CPU registers. The memory and registers of the I/O devices are mapped to (associated with) address values. AVR MCUs come with at least 128 bytes of internal SRAM, the low 32 of which is also the register file. Some microcontroller architectures do still use memory-mapped registers, including old designs like 8051, and even some more recent designs like PIC microcontrolers and AVR (an 8-bit RISC with thirty-two 8-bit registers). The chances you would encounter a mainstream CPU (not microcontroller) with memory-mapped registers these days are slim to none. They were almost all designed in the 1970's and are part of history now. The Bits Register Link column in the table below provides the mapping on the width of the data read within the 32-bit bus. RAM).Īs mentioned in comments, there do exist CPUs with memory-mapped CPU registers. Memory Mapped Register (MMR) Tables The address buses to read and write from the MMR registers are 10 bits wide, while the read and write data buses are configured to be 32 bits. In other words, they are accessed just like any other memory (e.g. I/O devices often have memory-mapped registers, where you write to or read from a specific address to set or get information or data. You can not access them through loads or stores to any memory address.Ī memory-mapped register is something which you access through an address or a pointer (in languages that have pointers). Based on the granularity, a CPU node controller configures MMIO range registers of the interconnect and other MMIO registers in IO nodes and CPU node. No, those registers are inside the actual CPU (or CPU core for multi-core CPUs). ![]()
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