Getting started with arm
There are many different variants of the ARM architecture and implementations that have evolved over time. The notation can be confusing. For instance, arm7 and armv7, are completely different. The first is a CPU implementation; the second is a CPU architecture. The architecture, also called a family, is a set of machine instructions (or ISA for instruction set architecture) that are generally compatible. See: Wikipedia’s list of ARM microarchitectures for more.
- [tag:thumb] - the first version consisted of a reduced set of 16bit instructions. thumb2, introduced with armv6, includes a mix of 16 and 32bit instructions, extended further in armv7 such that it can do most things the normal ARM ISA can.
- [tag:neon] - a SIMD extension for ARM CPUs
- [tag:cortex-m] - an embedded ISA of the armv7 that only supports thumb2.
- [tag:cortex-a] - the application version of armv7 ISA.
- [tag:arm64] - the eighth arm architecture (armv8) includes 64bit registers.
- [tag:trust-zone] - a security feature in some armv6, armv8 and armv7 CPUs.
- [tag:amba] - bus or interconnect specification used between CPUs and peripherals.
Other CPU specific tags exist, such as [tag:cortex-m3]. Often those posts apply to other cortex-m CPUs and/or the difference between the versions is important to understand. Also newer future CPUs may extend a specific CPU and questions in that tag maybe relevant.
If you are only posting to the tag [tag:arm] try to give some specifics about the system you are using.
Build and Run ARM Assembly
To run ARM assembly code you will need a machine with an ARM processor.
If you are on Linux you can use the following commands to compile your program:
as -o prog_object.o my_prog_source.s
Link to get the executable:
ld -o run_prog prog_object.o
If you run
echo $? it will return the value stored in R0