From 33b2228e1fc046de8677b50331507f7ef93f3fe3 Mon Sep 17 00:00:00 2001 From: Doug Evans Date: Sat, 21 Dec 2002 22:19:22 +0000 Subject: [PATCH] comment tweaks --- types.scm | 22 ++++++++++++++-------- 1 file changed, 14 insertions(+), 8 deletions(-) diff --git a/types.scm b/types.scm index 27bf707..7ad9f45 100644 --- a/types.scm +++ b/types.scm @@ -161,14 +161,14 @@ ; lsb0? = #t ; insn-word-length = 2 ; endian = little -; [note that this is the little endian canonical form +; [note that this is the little endian canonical form (*) ; - word length is irrelevant] ; | 7 ... 0 | 15 ... 8 | 23 ... 16 | 31 ... 24 | 39 ... 32 | 47 ... 40 | ; ; lsb0? = #f ; insn-word-length = 2 ; endian = big -; [note that this is the big endian canonical form +; [note that this is the big endian canonical form (*) ; - word length is irrelevant] ; | 0 ... 7 | 8 ... 15 | 16 ... 23 | 24 ... 31 | 32 ... 39 | 40 ... 47 | ; @@ -177,11 +177,16 @@ ; endian = big ; | 15 ... 8 | 7 ... 0 | 31 ... 24 | 23 ... 16 | 47 ... 40 | 39 ... 32 | ; -; While there are no current examples, the intent is to not preclude -; situations where each "word" in an insn isn't the same size. For example a -; 48 bit insn with a 16 bit opcode and a 32 bit immediate value might [but not -; necessarily] consist of one 16 bit "word" and one 32 bit "word". -; Bitranges support this situation, however none of the rest of the code does. +; (*) NOTE: This canonical form should not be confused with what might be +; called the canonical form when writing .cpu ifield descriptions: lsb0? = #f. +; The ifield canonical form is lsb0? = #f because the starting bit number of +; ifields is defined to be the MSB. +; --- +; At the bitrange level, insns with different sized words is supported. +; This is because each contains the specs of the word it resides in. +; For example a 48 bit insn with a 16 bit opcode and a 32 bit immediate value +; might [but not necessarily] consist of one 16 bit "word" and one 32 bit +; "word". ; ; Examples: ; @@ -214,7 +219,8 @@ ; [this allows the bitrange to be independent of the lengths ; of words preceding this one] word-offset - ; starting bit number within the word + ; starting bit number within the word, + ; this is the MSB of the bitrange within the word ; [externally, = word-offset + start] start ; number of bits in the value -- 2.43.5