Hardware software trade offs
Higher performance with more bang for the buck is today's microprocessor game. We have the architectural expertise and technology to design radically new microprocessors, to craft new and sophisticated ISAs Instruction Set Architectures. Instead, the trend is to extend existing ISAs, giving performance boosts hardware software trade offs current microprocessors. These extensions would be so much unused silicon if not for hardware software trade offs and compiler support. It is the development software that ensures effective employment of new ISA features.
Thus ISA extensions appear hardware software trade offs software libraries or compiler enhancements for programmer and compiler use. Cygnus Solutions provides development tools and compilers for over 30 architectures and around different microprocessors, a number of which incorporate ISA extensions.
ISA extensions combine the better of two worlds: For example if you have a project and you choose a 68K or a SPARC, you have a wide range of operating, development and application software available for use. New architectures need time to build up an equivalent software base. Extensions let microprocessor architects incrementally add new technology as it comes on line. Some ISA extensions now emerging include:.
However, it keeps the bit datapath. This tactic cuts RISC code bloat, especially for code intensive applications but keeps bit data processing capabilities. The dynamic part is that programs can switch from the bit to bit ISAs as needed while running. The code is compiled for mixed or bit ISA operation. These hardware software trade offs adding MAC multiply-accumulate instructions and other interactive, math-oriented processing.
Java Software Engine Java is a software extension to hardware. Java started out with a byte-code interpreter in its hardware software trade offs engine. Compiled versions of Java are emerging to deliver higher, C-level performance. The GNU tools are highly modular and designed to support a wide range of architectures and processors. It also shows where ISA extensions are added to the flow.
ISA extensions do more than just add a "mess" of instructions and leave their use to assembly writer and compiler folk. These new instructions are designed to work together, to support one another and to provide new capabilities to the existing ISA. For example, for DSP extensions, the new instructions were created to allow developers to set up and iterate through a DSP loop accumulating values for a series or for matrix or vector operating. The "model" in hardware software trade offs case includes setting up addressing pointers, setting loop values and running an iterative DSP processing loop.
The key to efficient DSP operation is to minimize "bookkeeping" operations and run very tight inner loop code. The "computing model" provides the model of behavior that programmers can emulate to craft efficient code. The compiler is also structured to optimize that "computing model" or way of coding. This goes beyond the traditional hardware software trade offs optimization, which is to optimize individual instructions or threads of instruction usage. Computing models make the point that ISA extensions are more than a few new instructions.
Instead, they are a collection of operations that collectively support a model of processing. The closer library and application code follows those models, the more efficient code execution will be.
To do this, to shrink bit instructions to bit instructions, the number of instructions and number of registers referenced are reduced. Smaller instruction word fields equal less hardware software trade offs and less register resources. Less register resources means that the compiler must be register stingy and users should minimize defined hardware software trade offs use. The benefits from using ISA extensions and deploying them in assembled and compiled hardware software trade offs is not trivial.
These extensions can deliver a great boost in performance or usability for specific application classes. Has bit instruction set and registers with bit data path. Instead, however, it provides a much more controlled, structured object-oriented development and runtime environment. These ISA extensions allow developers to stay with standard microprocessor architectures, yet get critical hardware software trade offs boosts or usability boosts for their applications.
Many consider the 68K to set the standard for acceptable embedded system code density. The 68K design team made a number of very effective architectural decisions, decisions that have proved themselves over time. The key design parameters for the 68K was that it had hardware software trade offs bit data path originally bit registers with a bit ALU and hardware software trade offs memory interface and bit instructions. Most instructions fit into bits with hardware software trade offs for addressing and immediate data.
This combination of bit instructions and bit data gave the 68K bit processing power with hardware software trade offs bit ISA code density. To do this RISC designers minimized the instruction set -- the less instructions, the less logic depth, and thus faster execution.
The hardware software trade offs instruction word has smaller fields. Thus, it can only execute a smaller set of instructions using a smaller register set since the OP hardware software trade offs field and register fields need to reduce to create 16 bit instructions. They came up with Thumb, which took a very clever approach to running a bit ISA. The trick was to pick a bit subset of the bit ARM ISA, with less registers and instructions to reduce the field sizes. The decoded instructions are then passed through an expansion block, that expands the decode to the bit form, and the decoded bit instructions are then passed on to the next stage in the pipeline.
The bit instructions are retrieved, decoded and then expanded to bit instructions for execution. The MIPS takes a similar approach. Figure 2 shows the decode expansion block that expands the bit instructions to bitters. Those have fixed bit ISAs and a bit datapath.
A mode or status bit sets 16 or bit ISA mode. That bit cannot be set at any time during execution. It can only be set during a call or return, insuring that or bit ISA operation is defined at hardware software trade offs function or subroutine level, or higher.
They run compiled code and the compiler compiles or bit ISA code. A switch or flag is set, and that indicates whether to compile a function or file as or bit code. The decision of what is or bit ISA code is made at compile time, not runtime. However, the generated code will set the proper ISA mode bit when switching from to bit code or vice versa.
To fit into 16 bits, the MIPS uses 5-bits for its major op code field and function field they were 6-bits3-bits for the register fields they were 5 bits. And it shrinks the immediate value field from to 5-bits. The bit ISA's restricted register set directly effects compiler register allocation strategy. With the normal MIPS ISA, when the compiler allocates registers for a complex expression, it normally feels free to allocate a new register any time hardware software trade offs is needed.
Usually there are enough registers, and if there are not enough, if too many registers are needed, some are merged or spilled to the stack. Other changes include adding a special stack pointer instead of using a general register. The MIPS only has 8 general registers, too few to use on as designated stack pointer. JALX jumps and saves the next address in a link register and is used for subroutine calls.
The JALR returns to the address in the link register. The ISA mode bit can also be changed when an exception occurs. Generally exceptions are handled by the system in full bit ISA mode. This becomes a problem since the MIPS calling convention is meant to pass floating-point values in the floating-point registers. The MIPS code cannot access that value. We fixed the problem by making sure that the compiler emits a bit stub for any bit function that took a floating-point argument. The stub copies the floating-point register into regular argument registers, and that then jump to the bit function.
The linker arranges for all calls from bit functions to go to the bit stub. If the bit stub is never called, the linker deletes it. When a bit function calls a function with a floating-point argument, the compiler adds a bit stub. The linker arranges the function call to go through the stub if calling a bit function; it will go directly to a bit function. Someone once noted that many applications manage to turn bit microprocessors into 8-bit processors.
Unfortunately, that's true for many standard programming tasks. These operations involve a bit processor searching for an 8-bit or character value, one byte at a time. Yes, you can speed it up by doing AND compares and testing on matches, but it still takes processing time. Another processing sink for inefficient cycles is 8-bit or bit pixel processing on a bit or bit data path. Rarely can such processing use the full datapath bandwidth of the CPU.
Hardware software trade offs it throttles down, processing to the graphic field size, and wastes datapath resources. Hardware software trade offs, for a bit system, one instruction can do eight 8-bit adds, compares, or logical AND s, for example. That is an 8X speed up. Cygnus Solutions was the first to produce a commercial compiler for V9 processors. It hardware software trade offs issue up to four instructions per pipeline cycle. It has four execution units: These operations, except for divide and square root, are fully pipelined.
They can complete out-of-order without stalling the execution of FGops. It also has 4 sets of FP condition code registers for more parallelism. Pixel information is typically stored as four 8-bit or bit integer values.
Typically these four values represent red, green, blue RGB and the alpha a information for the pixel.
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