The code is a bit difficult to understand, but it represents the 'normal'
path for processing a DECtape word. The code always flows all the
way to the break.
For start of block, there's extra code to check for a timing error; but
then the first word is processed (case 0).
For a normal word, a 3-cycle data break is done - increment word
count and current address, check for word count overflow, put the
word in the buffer; but then check for end of block (case DTO_WCO).
If the word count has already overflowed, just check for end of block.
So yes, the end of case 0 should be labeled 'fall through' as well.
FNC_WRIT has the same structure and needs the same comment.
CID Action
1416081 changed variable answer to int
1416082 checked returned values with ASSURE - read error means corrupted target code.
1416088 added return
1416109 This fallthru was intentional - duplicated code to make coverity happy
1416111 This fallthru was intentional - duplicated code to make coverity happy
1416116 This fallthru was intentional - duplicated code to make coverity happy
1416117 This fallthru was intentional - duplicated code to make coverity happy
1416124 protected against negative return
1416142 added ASSURE, however this case won't happen since reg_intpending==true implies positive int level
1416145 checked non-NULL, return SCPE_ARG if NULL
1416150 since only 2 drives are supported, fdc_selected is decoded to 0 and 1 only (allowed 2 and 3 before)
1416152 restrict to 2 drives only
1416166 checked value with ASSURE
1416101 typo: should have been resx
1416106 unnecessary code removed
1416110 this fallthru was intentional - duplicated code to make coverity happy
1416112 this fallthru was intentional - duplicated code to make coverity happy
1416148 change condition to check for negative value
1416179 break was remainder from former logic - removed
1415866 code was remainder from former unimplemented instruction trap - removed
the opcode table first word consists of bits:
<7> = FPD is legal for this opcode.
<4:6> = number of specifiers for unimplemented opcodes (VAX subsets)
<3> = unused
<0:2> = number of specifiers
The mask used to be 0x70. The convention is that x_M_y is a mask value
<right-justified>, for a macro like:
#define get_foo(x) (((x) >> x_V_foo) & x_M_foo)
For a subset VAX (like the 3900), the unimplemented opcodes are those
