VM – Objects

Implementing an Object Index to replace the current 32 bit register array can be done in at least two ways.

Firstly I need to use a SRAM buffer to hold objects rather than the current 32 bit register array, and I need to replace the 16 bit index in the Data Descriptor with a 16 bit Offset. This gives us a maximum of 64Kb data range per module, but that is more than I need. We should probably rename the Data Descriptor to Object Descriptor ?

I can now replace the 16 bit register index with a 32 bit data descriptor everywhere in the instructions, or I can use a 16 bit Object Index and implement a Object Index table. The first will use more flash, but I am a bit concerned about performance on the last one. If I use a lookup table in Flash we will be reading an instruction that will need to lookup multiple data descriptors – and reading from flash is slow. We could of cause move the table to SRAM as this is very small table (40 bytes on 10 variables).

I think I will prefer to just use 32 bit Data Descriptors on the instruction set to keep things simple, but I need to do some math over Flash/SRAM usage and think through the full impact.

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