Script for Laboratory: Designing embedded ASIPs - CES

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• Review the arith.cgd file on i80pc06. This file is automatically created by meistercg and it contains all CoSy rules for arithmetic instructions. You can find this file in ~/buildtrees/{COMPILER_PREFIX}cc/build/engines/{COMPILER_PREFIX }cg/cgd/ Inspect the rule for your instruction which is not used and make sure, that the combination of nodes (e.g. mirAdd) and the condition match your assembly instruction and that this rule can really be used in your elementary C-code. Details about the CoSy rules can be found in Chapter 8.2.1. 8.3.2 Typical problems while using the CoSy compiler There are some known problems with the created compiler binary, due to faulty rule descriptions. Sometimes it even can happens, that the compiler binary aborts the compilation of your application with a run time error message, as some cases of an application seems not to be covered by the created set of rules at all. Here we provide a list of workarounds that you really should consider, when your program is working incorrect, or the compiler is crashing. • Every function has to return a value, i.e. do not use ‘void’ functions! The reason for this is, that the compiler sometimes uses the ‘return register’ e.g. as loop counter, when in this loop a void function is called, as it thinks, this void function will not need the return register. But if this void function itself calls a function, which overwrites the return register, then the loop counter is lost. • You cannot use structs as parameters (or return value) of functions. This needs copying all members of the struct to the function. Instead you can use pointers to structs. • Together with inline assembly (see Chapter 8.4) there are additional problems with structs. Sometimes the compiler aborts with a run time error message. In such cases it often helps to modify the C-code such, that there are some independent instructions between the struct usage and the inline assembly call. • Sometimes there are problems with initializing arrays that are declared locally in functions, e.g. “int a[] = {23, 42}”. This can result in a run time error message, as the compiler needs a rule for a parallel copy from the initial array ({23, 24}) to the memory space of the array (a), but such a rule was not defined. As workaround you can make the array global (or static) or you can separate declaration and definition of the array, i.e. “int a[2]; a[0]=23; a[1]=42;”. 8.4 Support for Inline Assembly (SINAS) It sometimes happens, that a custom instruction is implemented correct in the compiler, but it is anyway not used, although it should be usable concerning the compiled C-Code. This happens very often in cases, where the custom instruction contains control flow structures, like an if-then-else construct. The reason for this behavior is, that the compiler was not able to match the specific instruction in his internal representation of the application. In such situations there are two possibilities to overcome the problem. The first possibility is to extend the compiler with an optimization engine, that is dedicated to finding places in the internal representation where the specific custom instruction can be used. This possibility is very time consuming while creating the compiler and has to be redone for every new custom - 76 -
instruction, as different custom instructions usually need different strategies for identifying them in the internal representation. The second possibility is to use inline assembly. Inline assembly is a porting of assembly code that is explicit written into the C-Code at the place, where it should be used. This way we can insert any custom instruction right into the C-Code without modifying the compiler. We can also insert small subroutines in a hand-optimized assembly version into the C-code. This possibility is time consuming while preparing the application, but for very complex custom instructions it is much faster than extending the compiler to automatically identify the instruction. First we will give a small example for the basic syntax for the CoSy specific version of inline assembly and later we will go into further details how the embedded assembly code can be parameterized. asm int example(int parameter1, int parameter2) { @[ // Some later explained directives can be placed here ] ; This comment is written to the created assembly file nop nop nop add @{}, @{parameter1}, @{parameter2} nop nop nop ; The @{parameter1} and @{parameter2} will be replaced by ; the used registers for those parameters. The @{} referrs ; to the register for the return value. } void main() { int a=5, b=7, c; c = example(a, b); } The created assembly file would look similar to the following (changes by the register allocations are marked): ... addi r1, r0, $5 addi r2, r0, $7 nop nop nop ; This comment is written to the created assembly file add r3, r1, r2 nop - 77 -
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Laboratory: “Designing Applicatio
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6 Validating the CPU in Prototyping
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Figure 1-1 GPPs, ASIPs and ASICs [H
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• Command line interpreter Intera
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i. Copying files: the cp command co
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. Copying via ssh: Not all machines
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dlx_basis Applications ModelSim mei
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makeCoSy contCoSy Filename Explanat
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3 Dlxsim Dlxsim [DLX-Package] is an
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Successful Successful dissolving di
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Instruction Description Instruction
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Option Description -dbb# (Debug Bas
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Page 27 and 28: Command Description stop {options}
Page 29 and 30: 3.3.2 Debugging with dlxsim This ch
Page 31 and 32: addComment1(); functionY(); addComm
Page 33 and 34: • If you manually want to write a
Page 35 and 36: 4.3 Tutorial for the “Flexible Ha
Page 37 and 38: in direction; The in keyword means
Page 39 and 40: amount : in std_logic_vector(7 down
Page 41 and 42: Add the three signals to the contro
Page 43 and 44: data_in : in std_logic_vector($W1 d
Page 45 and 46: 5 ModelSim ModelSim is a full-featu
Page 47 and 48: 5.1.3 Compile the project Figure 5-
Page 49 and 50: Mark the wave.do file in your Model
Page 51 and 52: Figure 5-6 ModelSim waves Signal Ex
Page 53 and 54: • Always invoke ModelSim in the s
Page 55 and 56: If you don’t already have a proje
Page 57 and 58: CPU VHDL Files have been generated
Page 59 and 60: After the TestData-files for your a
Page 61 and 62: However, you can’t force the synt
Page 63 and 64: Timing (Timing Analyzer)” will op
Page 65 and 66: 7 Power estimation In this tutorial
Page 67 and 68: - Start the simulation (Simulate/ s
Page 69 and 70: 8 CoSy compiler The CoSy compiler d
Page 71 and 72: When you manually have to fix some
Page 73 and 74: of the makeCoSy script. If an error
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Page 79 and 80: Directive Explanation .restrict .ch
Page 81 and 82: Now we will demonstrate how you can
Page 83 and 84: the user changes the value of the b
Page 85 and 86: • Huge decrease of cycle count
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Page 89 and 90: Table of Figures Figure 1-1 GPPs, A
Page 91: References [CES] Homepage of the Ch
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