Thursday, July 24, 2008

RhoZeta Excel-Python-OpenGL Demo

In this demo I will show you how to use the RhoZeta Python-Excel bindings to create a non-blocking assignment spreadsheet iteration thread and an OpenGL window to draw cells. This older demo shows more Python evaluate-able code in Excel spreadsheet cells with RhoZeta. Feel free to leave comments and suggestions for future demos.

RhoZeta is a Python spreadsheet language with Excel bindings to allow programmers to process spreadsheet formulas through a Python backend. The cell values are forwarded to the Excel frontend to display in the current Visible Range. The longer term goal is to demonstrate how the spreadsheet iteration model can serve as an open framework for accelerated computing on FPGA, GPU, and Multicore architectures. These architectures consist of physical arrays of cells designed for dataflow processing and vector data parallelism. This locality-constrained, vector-oriented, dataflow programming model finds obvious expression in a spreadsheet. I've argued that this model effectively replaces the von Neumann instruction stream as the primitive model for designing systems on parallel hardware.

The code for this demo is up on the Catalyst Accelerated Computing Trac. Running alone does not require PyOpenGL but you wont get the OpenGL window. depends on PyOpenGL (which requires setuptools to install) and win32com (included with Python for windows aka PythonWin). I've only tested this with Excel 2007, but I think the underlying COM interface is still compatible with 2003.

Firstly: this is hacking and not a product yet. DO NOT START THIS WITH ANY OPEN WORKBOOKS OR YOU MAY LOSE YOUR DATA. You were warned.

Run and Excel and an OpenGL Window should pop-up:

Put the function "=time.clock()" into cell A1. If the cell manager is functioning the value of A1 should be forward to the Excel frontend on a Timeout.

Since this is a non-blocking assignment interpretter, placing "=A1" into cell A2 will cause A2 to act like a register reflecting the value of A1 from the previous iteration:

We use the fact that A2 is A1 delayed by an iteration cycle to determine the time difference between two cells:

We can repeat the register-delay structure to track the iteration time for multiple clock cycles:

If we repeat this register structure 4 times we may take the average iteration time (try to click-and-drag the formula from cell B4, it should work).

I also whipped up some code to pull the Row Heights and Column Widths into an OpenGL drawing window with some MouseOver detection (only 2-D... I need to learn how to do selection correctly and in 3-D). The OpenGL window synchronizes with Excel when you click in the window. The top left cell should be the same as the top left cell in your Excel visible range. There's also code to draw a bar-graph of the selected cells data, but you'll have to tinker. Expect the next OpenGL demo to be even cooler.

The goal here was to demonstrate a spreadsheet that iterates continuously following a non-blocking semantic as in Verilog non-blocking assignments: each cell is computed from the same pool of values and the next values are assigned simultaneously. Ordinary Excel iteration interprets according to blocking assignment semantics: each cell is computed and assigned in the order in which the table is read. Under Excel's ordinary blocking assignments, assigning A2 the formla "=A1" would read the newly assigned value from the current iteration because A2 comes after A1. We can do shift registers in blocking assignments by reversing the order ie assigning A1 to "=A2"

Cells in a blocking assignment iteration are non-commutable, the location of the cell matters to the interpretation. Non-blocking assigned cells may be moved freely. A third assignment type, asynchronous assignment, computes a new value whenever the cell's precedents change as a combinatorial circuit would. Cells with an asynchronous assignment are also commutable. It is generally possible to mix these forms of assignments as in VHDL with mixed variables and signals and continuous assignments. We could presumably support a syntax to replace the leading "=" to allow mixed modes.

The iteration timing here is a poor because cells are being dynamically parsed and interpreted by Python using the eval function. We know how to do better by JIT compiling sheet iteration in Python (some code is up in our Trac to do this). The next step in performance is to statically propagate types and compile sheet iteration pipelines to C so we can fork new threads onto a multicore/GPU/FPGA-core and parallelize sheet iteration. We also know how to get this sheet to iterate deterministically with dedicated resources in under 2 nanoseconds using an FPGA synthesis toolchain -- of course measuring the average iteration time for a deterministic iterator would be silly.

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