But: I think recent microcodes do actually include code (see Xucode) but that code is meant to be the behavior of advanced instructions and not designed to be something that tells the CPU what to do from the moment it's powered on. My opinion: CPU microcode isn't firmware - CPU microcode sets the configuration of internal connections/parameters in the CPU. the host has to have some way of externally programming the peripheral's RAM directly and resetting the peripheral's CPU but not the peripheral's RAM. Maclocks Locks For Every MacBook Home Shop by Product Laptop Locks Laptop Locks Sort By Universal Tablet Lock Adhesive Security Plate From 39. The sound chip in Nintendo's Super NES is an example, on power on/reset it has a 64 byte boot ROM that does nothing but wait for data to come in from the main 65816 CPU and then runs that code when received. it has to have some small ROM that does nothing but wait for an image to come in from a bus (USB, etc.) and then execute.

If the CPU is embedded in a peripheral, then: What I always understood firmware to be is: a ROM that gives a CPU something to do when power is applied, as RAM is blank on power on and things like storage devices can't just put stuff in RAM without being directed by the CPU (which doesn't have code to do that at power on unless provided by a ROM).ĭepending on the scope of the device (from multipurpose PC down to single-purpose things like microwaves, gas pumps, hard drives, LCD controllers) the firmware may just allow an operating system to be loaded or actually be all the code the appliance needs for its CPU.

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