Increase maximum number of harts

[bluewww]

OpenOCD can't deal with systems that have more than 32 harts.

[timsifive]

How much more memory does OpenOCD use when you do this? To keep supporting -rtos riscv (which is deprecated and will be removed eventually) I think memory usage is O(n^2) on the number of harts. Once we get rid of that we should be able to remove the limit altogether.

[bluewww]

It increases memory usage from 2.4MiB to 45.1MiB on my machine.

[timsifive]

How many harts are actually configured in that measurement?

[bluewww]

One. Aren't we interested how this patch affects the regular case (low hart count/low hart id number since that seems to be the same)?

[timsifive]

So if 1 hart uses 43MiB more after this change, then (assuming somebody was using OpenOCD for) a 32-hart system using might incur 1.3GiB of extra memory usage. That's kind of high.

Do you need the full 1024 harts, or did you just pick a number that should be good for a long time? I'd be a lot more comfortable with half or a quarter of this memory increase.

Over the long term -rtos riscv is going to go away, we can get rid of RISCV_MAX_HARTS, and memory usage won't blow up the way it does currently when increasing that number.

[bluewww]

Well in our case it's a combination of both: We have setups with more than 32 cores and the maximum hartid is just slightly below 1000 ish.
Are there any low hanging fruits to alleviate the memory issues?

[timsifive]

Turns out there's some very low hanging fruit: #431
Once that merges, your change will be fine.