Recherche avancée

Sur d’autres sites (9926)

• ARM inline asm secrets

  6 juillet 2010, par Mans — ARM, Compilers

  Although I generally recommend against using GCC inline assembly, preferring instead pure assembly code in separate files, there are occasions where inline is the appropriate solution. Should one, at a time like this, turn to the GCC documentation for guidance, one must be prepared for a degree of disappointment. As it happens, much of the inline asm syntax is left entirely undocumented. This article attempts to fill in some of the blanks for the ARM target.
  

  Constraints

  Each operand of an inline asm block is described by a constraint string encoding the valid representations of the operand in the generated assembly. For example the “r” code denotes a general-purpose register. In addition to the standard constraints, ARM allows a number of special codes, only some of which are documented. The full list, including a brief description, is available in the constraints.md file in the GCC source tree. The following table is an extract from this file consisting of the codes which are meaningful in an inline asm block (a few are only useful in the machine description itself).

  f	Legacy FPA registers f0-f7.
  t	The VFP registers s0-s31.
  v	The Cirrus Maverick co-processor registers.
  w	The VFP registers d0-d15, or d0-d31 for VFPv3.
  x	The VFP registers d0-d7.
  y	The Intel iWMMX co-processor registers.
  z	The Intel iWMMX GR registers.
  l	In Thumb state the core registers r0-r7.
  h	In Thumb state the core registers r8-r15.
  j	A constant suitable for a MOVW instruction. (ARM/Thumb-2)
  b	Thumb only. The union of the low registers and the stack register.
  I	In ARM/Thumb-2 state a constant that can be used as an immediate value in a Data Processing instruction. In Thumb-1 state a constant in the range 0 to 255.
  J	In ARM/Thumb-2 state a constant in the range -4095 to 4095. In Thumb-1 state a constant in the range -255 to -1.
  K	In ARM/Thumb-2 state a constant that satisfies the I constraint if inverted. In Thumb-1 state a constant that satisfies the I constraint multiplied by any power of 2.
  L	In ARM/Thumb-2 state a constant that satisfies the I constraint if negated. In Thumb-1 state a constant in the range -7 to 7.
  M	In Thumb-1 state a constant that is a multiple of 4 in the range 0 to 1020.
  N	Thumb-1 state a constant in the range 0 to 31.
  O	In Thumb-1 state a constant that is a multiple of 4 in the range -508 to 508.
  Pa	In Thumb-1 state a constant in the range -510 to +510
  Pb	In Thumb-1 state a constant in the range -262 to +262
  Ps	In Thumb-2 state a constant in the range -255 to +255
  Pt	In Thumb-2 state a constant in the range -7 to +7
  G	In ARM/Thumb-2 state a valid FPA immediate constant.
  H	In ARM/Thumb-2 state a valid FPA immediate constant when negated.
  Da	In ARM/Thumb-2 state a const_int, const_double or const_vector that can be generated with two Data Processing insns.
  Db	In ARM/Thumb-2 state a const_int, const_double or const_vector that can be generated with three Data Processing insns.
  Dc	In ARM/Thumb-2 state a const_int, const_double or const_vector that can be generated with four Data Processing insns. This pattern is disabled if optimizing for space or when we have load-delay slots to fill.
  Dn	In ARM/Thumb-2 state a const_vector which can be loaded with a Neon vmov immediate instruction.
  Dl	In ARM/Thumb-2 state a const_vector which can be used with a Neon vorr or vbic instruction.
  DL	In ARM/Thumb-2 state a const_vector which can be used with a Neon vorn or vand instruction.
  Dv	In ARM/Thumb-2 state a const_double which can be used with a VFP fconsts instruction.
  Dy	In ARM/Thumb-2 state a const_double which can be used with a VFP fconstd instruction.
  Ut	In ARM/Thumb-2 state an address valid for loading/storing opaque structure types wider than TImode.
  Uv	In ARM/Thumb-2 state a valid VFP load/store address.
  Uy	In ARM/Thumb-2 state a valid iWMMX load/store address.
  Un	In ARM/Thumb-2 state a valid address for Neon doubleword vector load/store instructions.
  Um	In ARM/Thumb-2 state a valid address for Neon element and structure load/store instructions.
  Us	In ARM/Thumb-2 state a valid address for non-offset loads/stores of quad-word values in four ARM registers.
  Uq	In ARM state an address valid in ldrsb instructions.
  Q	In ARM/Thumb-2 state an address that is a single base register.

  Operand codes

  Within the text of an inline asm block, operands are referenced as %0, %1 etc. Register operands are printed as rN, memory operands as [rN, #offset], and so forth. In some situations, for example with operands occupying multiple registers, more detailed control of the output may be required, and once again, an undocumented feature comes to our rescue.

  Special code letters inserted between the % and the operand number alter the output from the default for each type of operand. The table below lists the more useful ones.

  c	An integer or symbol address without a preceding # sign
  B	Bitwise inverse of integer or symbol without a preceding #
  L	The low 16 bits of an immediate constant
  m	The base register of a memory operand
  M	A register range suitable for LDM/STM
  H	The highest-numbered register of a pair
  Q	The least significant register of a pair
  R	The most significant register of a pair
  P	A double-precision VFP register
  p	The high single-precision register of a VFP double-precision register
  q	A NEON quad register
  e	The low doubleword register of a NEON quad register
  f	The high doubleword register of a NEON quad register
  h	A range of VFP/NEON registers suitable for VLD1/VST1
  A	A memory operand for a VLD1/VST1 instruction
  y	S register as indexed D register, e.g. s5 becomes d2[1]

• Museum of Multimedia Software, Part 1

  14 août 2010, par Multimedia Mike — Software Museum

  Many years ago, I found a boneyard of old software, much of it related to the creation and processing of multimedia. I was permitted to liberate anything of my choosing from this cache. This is the same pile where I found this Apple QuickTime format spec as well as this perfect form factor floppy disc box. So I have been sitting on the stuff for awhile.

  I thought I might get the chance to study it a bit more closely one day. But now I’m interested in getting rid of it. Before I do, it’s more or less traditional for me to photograph it and post it on one blog or another. Also, if you know of any software collection groups who would be interested in taking this stuff off my hands, do let me know.

  As usual, click a picture for a much larger image.

  Paracomp FilmMaker
  This is easily the most distinctive piece in this collection and it’s easy to see why— the software is packaged in a film cannister. Still sealed, and I don’t have a good reason to open it now.

  
  
  

  "The Professional Animation/Presentation Program for the Macintosh." No copyright date on the packaging, though the front does mention a 1990 award. System requirements : Mac OS 6.0.5, 5 MB RAM, 32-bit QuickDraw, math coprocessor.

  Strata VideoShop
  Version 4.5 (and not for resale), still shrink-wrapped. "The Digital Video Editor for Creative Professionals."

  
  
  

  System requirements : PowerMac with 5 MB RAM (8 MB recommended), Mac OS 7.5.

  BeatWare e-Picture
  "The Professional’s Choice for Designing Animated Web Graphics." Claims a best of show award for 1999 MacWorld New York Expo.

  
  
  

  System requirements : PowerMac with Mac OS 8, 32MB RAM, 10 MB of HD space and a 256-color adapter.

  BeatWare eZ-Motion
  Another offering from BeatWare. "The fastest and easiest way to create animations and graphics for the Web."

  
  
  

  This one is for either Mac or Windows. 32 MB RAM and 25 MB HD space required. Works with Mac OS 8.5, 8.6, or 9.0, or Windows 98, NT, or 2000.

  Much more to come...

• 2 GB Should Be Enough For Me

  31 août 2010, par Multimedia Mike — General

  My new EeePC 1201PN netbook has 2 GB of RAM. Call me shortsighted but I feel like “that ought to be enough for me”. I’m not trying to claim that it ought to be enough for everyone. I am, however, questioning the utility of swap space for those skilled in the art of computing.

  
  
  Technology marches on : This ancient 128 MB RAM module is larger than my digital camera’s battery charger… and I just realized that comparison doesn’t make any sense
  

  Does anyone else have this issue ? It has gotten to the point where I deliberately disable swap partitions on Linux desktops I’m using ('swapoff -a'), and try not to allocate a swap partition during install time. I’m encountering Linux installers that seem to be making it tougher to do this, essentially pleading with you to create a swap partition– “Seriously, you might need 8 total gigabytes of virtual memory one day.” I’m of the opinion that if 2 GB of physical memory isn’t enough for my normal operation, I might need to re-examine my processes.

  In the course of my normal computer usage (which is definitely not normal by the standard of a normal computer user), swap space is just another way for the software to screw things up behind the scenes. In this case, the mistake is performance-related as the software makes poor decisions about what needs to be kept in RAM.

  And then there are the netbook-oriented Linux distributions that insisted upon setting aside as swap 1/2 gigabyte of the already constrained 4 gigabytes of my Eee PC 701′s on-board flash memory, never offering the choice to opt out of swap space during installation. Earmarking flash memory for swap space is generally regarded as exceptionally poor form. To be fair, I don’t know that SSD has been all that prevalent in netbooks since the very earliest units in the netbook epoch.

  Am I alone in this ? Does anyone else prefer to keep all of their memory physical in this day and age ?