[docs] Explain how to use the IPU Model

docs/src/poplar.md

@@ -52,3 +52,19 @@ You can slice a tensor with the usual Julia notation `tensor[index1:index2]`, th
 ```@autodocs
 Modules = [IPUToolkit.Poplar]
 ```
+
+## Using `IPUToolkit.jl` without an IPU
+
+While this package requires a physical IPU to use all the available features, you can still experiment with the IPU programming model even if you do not have access to a hardwre IPU.
+The Poplar SDK provides a feature called IPU Model, which is a software emulation of the behaviour of the IPU hardware.
+The IPU model comes with [some limitations](https://docs.graphcore.ai/projects/poplar-user-guide/en/latest/poplar_programs.html#programming-with-poplar), but it can be useful for testing or debugging.
+
+To use the IPU model in `IPUToolkit.jl`, define the device of your IPU program with `Poplar.IPUModelCreateDevice` (which calls [`IPUModel::createDevice`](https://docs.graphcore.ai/projects/poplar-api/en/3.4.0/poplar/profiling/IPUModel.html#_CPPv4NK6poplar8IPUModel12createDeviceE11OptionFlagsbj) under the hood):
+```julia
+model = Poplar.IPUModel()
+device = Poplar.IPUModelCreateDevice(model)
+# Then the rest of the program continues as usual
+target = Poplar.DeviceGetTarget(device)
+graph = Poplar.Graph(target)
+# ...
+```