Compiler Error: Multiple channel write sites.

For future reference, "Compiler Error: Multiple channel write sites." means that you are writing to the same channel from multiple locations in your code, which is not allowed. Each channel can only have one read and one write port. When you use SIMD, the compiler will try to extend the kernel pipeline to run multiple work-items in parallel, and if you have a channel read or write in your code, this will result in multiple work-items trying to read from or write to the same channel at the same time which is not allowed. SIMD and kernel pipeline replication (num_compute_units) are not supported for NDRange kernels that have channels.