I have been following j lynch tutorial from atmel for developing small programms for at91sam7s256 (microcontroller). I have done a bit tinkering and used arm-none-eabi instead of arm-elf (old one). By default i found that gcc compiles assuming -march=armv4t even if one does not mention anything about chip. How much difference it would if i use -mcpu=arm7tdmi?
Even searching a lot on google i could not find a detailed tutorial which would explain all possible command like options including separate linker options,assembler and objcopy options like -MAP etc.
Can you provide any such material where all possibilities are explained?
Providing information about the specific processor gives the compiler additional information for selecting the most efficient mix of instructions, and the most efficient way of scheduling those instructions. It depends very much on the specific processor how much performance difference explicitly specifying -mcpu makes. There could be no difference whatsoever - the only way to know is to measure.
But in general - if you are building a specific image for a specific device, then you should provide the compiler with as much information as possible.
Note: your current instance of gcc compiles assuming -march=armv4t - this is certainly not a universal guarantee for all arm gcc toolchains.