xerox 19790306 NoteTaker Smalltalk Conventions free download

File name 19790306_NoteTaker_Smalltalk_Conventions.pdf

NotcTakcr Smalltalk Conventions rn1is is a working document. Send protests to: Ted Kaehler Filed on: [IVY] NoteTakcLConventions This is version 5 on March 6, 1979 (Changes are underlined) Object Pointer Space A pointer to an object is called an OOP (ordinary object pointer). The 16 bits of an oop are apportioned as follows: oop = xxxx xxxx xxx x xxOO lbe' oop is a pointer to an object. The oop is the actual displacement in the OT of the entry of this object. The first oop is 0 and the last actual oop may be as big as OEFFC hex. oop = xxxx xxxx xxxx xxxI TIlis is the oop of an integer. The value of the integer is oop/2. oop = xxx x xxxx xxxx xxIO (Not yet specified) Physical Memory The bottom few K of physical memory are local to the processor. lbe entire space is divided as follows (all addresses are byte addresses in hex): 00000 (CS points here) Local memory for interpreter, storage management, interrupt vector. 02000 (Local memory ends at 02000 assuming 8K bytes of it). OT is lip to 15K entries of 4 bytes apiece. 10000 Data area. (actual smalltalk objects reside here). 3FFFF (end of physical memory 256K bytes). FFFFO Bootstrap locations for 8086 FFFFF (end of virtual memory 1M bytes). Object Table (OT) The object table contains a two word entry for each object and is indexed by the oop (plus OTbase) off the code segment register. 'The bit fonnat follows (Note that I am showing the bits as high:low but in memory the bytes are reversed): rrrr rrrr uuut tttv (bytes 1,0) ssss ssss ssss ssss (bytes 3,2) where r is REF the reference count, u are unused bits (possibly for garbage collector status), t is TOFF the core address off.~et, v is CLL (core longer than length, for intlated allocation), and s is TSEG the core address segment origin. ';'/e will use the LDS instruction to load the first OT word into register SI and the second word into segment register DS. Subsequent MOV instructions used to access the data fields of the object compute U1e effective address as DS*16 + SI. Notice that the v bit is anded out to give a zero bit Ulcre. Thus the TOPr' field overlaps the TSEa field by one bit. TOFt<' and TSEG are normalized so that negative offsets of up to 8 bytes are allowed on SI.DS. After anding out the REF, u. and v fields of SI, the core address of tile field ends up being ssss ssss ssss ssss 0000 + t tttO + offset. 2 Nonnalization applies to both objects and free blocks, thus the norma1ized core address in an OT entry will survive many allocations and frces. A nonnalization is only done during an allocation which must carve