From: Luke Kenneth Casson Leighton Date: Tue, 31 Mar 2020 10:49:49 +0000 (+0100) Subject: whitespace X-Git-Tag: convert-csv-opcode-to-binary~3012 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=0c109d84f46706b9b3fa7f7fcda794e5f8f81017;p=libreriscv.git whitespace --- diff --git a/openpower/isans_letter.mdwn b/openpower/isans_letter.mdwn index 5d9d313de..81f7379db 100644 --- a/openpower/isans_letter.mdwn +++ b/openpower/isans_letter.mdwn @@ -1,53 +1,53 @@ (Draft Status) -# Letter regarding ISAMUX / NS - -This is a quick overview of the changes that we are proposing to the PowerPC -instruction set. - -## Overview - -The PowerPC Instruction Set Architecture (ISA) is an abstract model of a -computer. This is what programmers use when they write programs for the machine, -even if indirectly via a compiler for a high level language. We must be -conservative in how we add to the ISA to: - -* not break existing programs - -* be mindful as to how others may wish to add to the ISA in the future - -This document describes our strategy. - - -## ISA modes and escape sequences - -New chips usually need to be able to run older (legacy) software that is -incompatible with the latest and greatest ISA. Eg: 64 bit chip must be able to -run older 16 bit and 32 bit software. - -To enable backwards compatability the CPU will be set into 'legacy' mode. This -is done with an ISA Mode switch, also known as ISA Muxing or ISA Namespaces. - -The operating system is able to quickly change between 'modern' ISA mode and -various legacy modes. - -Another technique is an ISA escape-sequence. This is a type of mode that is -only operational for a short time, unlike 32 or 64 bit which would be for the -entire run of a program. - - -## What are we adding to the ISA - -When high quality graphical display were developed the CPUs at the time were -shown to not be able to run the display fast enough. The solution was the use of -Graphics cards, these are specialised computers that are good at rendering -pixels; often by doing the same thing in different parts of the screen at the -same time (in parallel). These specialised computers are called Graphical -Processing Units (GPUs). - -The parallelism of some GPUs is thousands. This has led to GPUs being used to -solve non graphical problems where high parallelism is useful. - +# Letter regarding ISAMUX / NS + +This is a quick overview of the changes that we are proposing to the PowerPC +instruction set. + +## Overview + +The PowerPC Instruction Set Architecture (ISA) is an abstract model of a +computer. This is what programmers use when they write programs for the machine, +even if indirectly via a compiler for a high level language. We must be +conservative in how we add to the ISA to: + +* not break existing programs + +* be mindful as to how others may wish to add to the ISA in the future + +This document describes our strategy. + + +## ISA modes and escape sequences + +New chips usually need to be able to run older (legacy) software that is +incompatible with the latest and greatest ISA. Eg: 64 bit chip must be able to +run older 16 bit and 32 bit software. + +To enable backwards compatability the CPU will be set into 'legacy' mode. This +is done with an ISA Mode switch, also known as ISA Muxing or ISA Namespaces. + +The operating system is able to quickly change between 'modern' ISA mode and +various legacy modes. + +Another technique is an ISA escape-sequence. This is a type of mode that is +only operational for a short time, unlike 32 or 64 bit which would be for the +entire run of a program. + + +## What are we adding to the ISA + +When high quality graphical display were developed the CPUs at the time were +shown to not be able to run the display fast enough. The solution was the use of +Graphics cards, these are specialised computers that are good at rendering +pixels; often by doing the same thing in different parts of the screen at the +same time (in parallel). These specialised computers are called Graphical +Processing Units (GPUs). + +The parallelism of some GPUs is thousands. This has led to GPUs being used to +solve non graphical problems where high parallelism is useful. + **break** # Letter regarding ISAMUX / NS