The Ember Console — System Architecture Design: Memory Map

The Ember console is a machine with a 32-bit architecture, capable of addressing up to 4 GB of memory. However, in practical terms, game systems from our target era, the 1980s or 1990s, contained much less memory. In fact, many early machines had only a few kilobytes of memory or less. Even into the 1990s, home machines still typically had just a few megabytes, and consoles sometimes even less.

Ember Complete Memory Map

Since the Ember console will initially be implemented as an emulator running on modern PCs, we can provide the virtual machine with as much memory as we want. On FPGA implementations, however, we will be much more limited. Even on relatively modest FPGA boards, we can expect to find a few megabytes of SDRAM and typically a few tens or hundreds of kilobytes of block RAM, or internal fast memory.

It is, however, common for developer versions of game consoles from companies like Sony, Nintendo, and others to contain more RAM than consumer versions. This extra memory can be used for debug versions of the applications and to capture performance data and logs during game development on the system. So, for the initial design, we will just assume 1 MB of System RAM and 1 MB of Video RAM with the expectation that any future hardware implementations will likely contain less RAM.

Software-Defined Memory Map

With the exception of the start addresses of System RAM, Video RAM, the Zero Page, and the High Page, the locations of the various segments described here are not defined in hardware, but rather by the firmware at startup. When the machine powers on, the CPU begins executing instructions at a fixed address in the High Page. This system program, or firmware, then configures various systems, sets values as needed, and calls the user application code, which will be loaded at address 0x00010000 (Page One) in System RAM.

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