diff options
| -rw-r--r-- | spec.org | 42 |
1 files changed, 36 insertions, 6 deletions
@@ -15,6 +15,18 @@ unsigned type <T> the signed version is simply S_<T>. | HWord | 32 | | Word | 64 | |-------+------| + +Generally, the abbreviations B, H and W are used for Byte, HWord and +Word respectively. The following table shows a comparison between the +data types where an entry (row and column) $A\times{B}$ refers to "How +many of A can I fit in B". +|-------+------+-------+------| +| | Byte | Hword | Word | +|-------+------+-------+------| +| Byte | 1 | 4 | 8 | +| HWord | 1/4 | 1 | 2 | +| Word | 1/8 | 1/2 | 1 | +|-------+------+-------+------| * WIP Instructions An instruction for the virtual machine is composed of an *opcode* and, potentially, an *operand*. An /opcode/ represents the behaviour of @@ -38,15 +50,33 @@ virtual machine. Any instruction (even with an operand) has one and only one byte sequence associated with it. * TODO Storage Two types of storage: -+ Data stack which all core VM routines manipulate and work on (FIFO) ++ Data stack which all core VM routines manipulate and work on (FILO) + + ~DS~ in shorthand, with indexing from 0 (referring to the top of the + stack) up to n (referring to the bottom of the stack). B(DS) + refers to the bytes in the stack (the default). + Register space which is generally reserved for user space code i.e. other than ~mov~ no other core VM routine manipulates the registers -* TODO Assembler conventions -The standard library is allowed to use the first 8 words (64 bytes) of -register space without regard to user applications, so it's -recommended to use register space from the 9th (72nd bit) word onwards -for user applications if standard library is to be used. + + ~R~ in shorthand, with indexing from 0 to $\infty$. +* TODO Standard library +Standard library subroutines reserve the first 16 words (128 bytes) of +register space (W(R)[0] to W(R)[15]). The first 8 words (W(R)[0] to +W(R)[7]) are generally considered "arguments" to the subroutine while +the remaining 8 words (W(R)[8] to W(R)[15]) are considered additional +space that the subroutine may access and mutate for internal purposes. + +The stack may have additional bytes pushed, which act as the "return +value" of the subroutine, but no bytes will be popped off (*Stack +Preservation*). + +If a subroutine requires more than 8 words for its arguments, then it +will use the stack. This is the only case where the stack is mutated +due to a subroutine call, as those arguments will always be popped off +the stack. + +Subroutines must always end in ~RET~. Therefore, they must always be +called via ~CALL~, never by ~JUMP~ (which will always cause error +prone behaviour). * Footnotes [fn:2] ~NOOP~, ~HALT~, ~MDELETE~, ~MSIZE~, ~JUMP_*~ |