Updated website to v1.34.3
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Jeff
Jeff Parsons
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322 changed files with 44633 additions and 457 deletions
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@ -1,14 +1,14 @@
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---
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layout: post
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title: The MACRO-10 Assembler, 50 Years Later
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date: 2017-02-28 22:00:00
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date: 2017-03-21 22:00:00
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permalink: /blog/2017/03/21/
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machines:
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- id: testka10
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type: pdp10
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config: /devices/pdp10/machine/ka10/test/debugger/machine.xml
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debugger: true
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commands: a 30724 /apps/pdp10/diags/klad/dakaa/MYDAKAA.MAC
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commands: a 30724 /apps/pdp10/diags/klad/dakaa/DAKAA.MAC
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---
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A few weeks ago, I finished my first cut of the *core* PDP-10 instructions in PDPjs. Most of my remaining work
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@ -51,9 +51,9 @@ Any machine that includes the PDPjs Debugger (like the machine below) now includ
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The above machine uses the Debugger's assemble ('a') command to assemble DEC's "DAKAA" diagnostic
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[KA10 Basic Instruction Diagnostic](/apps/pdp10/diags/klad/dakaa/) and load the resulting code at address 30724:
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a 30724 /apps/pdp10/diags/klad/dakaa/MYDAKAA.MAC
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a 30724 /apps/pdp10/diags/klad/dakaa/DAKAA.MAC
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The Debugger invokes the MACRO-10 mini-assembler whenever the argument following the target address appears to be a URL.
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The Debugger invokes the MACRO-10 mini-assembler whenever the target address is followed by an argument ending with ".MAC".
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As previously described in the section on [PDPjs PDP-10 Opcode Tests](/apps/pdp10/tests/opcodes/), the Debugger already
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allowed you to assemble instructions directly into memory (eg, `a 100 hrli 1,111111`). This "immediate mode" feature is provided
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@ -73,7 +73,7 @@ This command differs from MACRO-10, which uses the `RADIX` pseudo-op to change t
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Obviously, it would be nice if both the Debugger and the MACRO-10 mini-assembler used matching commands, but the PCjs debuggers
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were written before MACRO-10 support was a consideration, so for now, that's life.
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All of the MACRO-10-style base prefixes are supported (^D for decimal, ^B for binary, an ^O for octal):
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All of the MACRO-10-style base prefixes are supported (**^D** for decimal, **^B** for binary, an **^O** for octal):
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>> print ^D27
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0o000000000033 27.
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@ -89,7 +89,7 @@ Expressions using angle brackets, another MACRO-10 convention, is also supported
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>> print ^D<45-22>
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0o000000000027 23.
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Note that the base modifier (^D) applies to the entire expression. You can also add MACRO-10 suffixes to integers:
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Note that the base modifier (**^D**) applies to the entire expression. You can also add MACRO-10 suffixes to integers:
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K: "kilo-", thousands
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M: "mega-", millions
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@ -118,8 +118,10 @@ so:
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Binary shifting using a **B** suffix is also supported. Note that MACRO-10 binary shifting is a "bit" unusual by today's
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standards, because the value after the **B**, *n*, is not a count but rather the desired bit position of the right-most bit of
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the original value. Moreover, MACRO-10 considers bit 0 the left-most bit, and bit 35 the right-most bit. Last but not least,
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*n* is always interpreted as a decimal value, regardless of the current base (radix). *n* can be converted to a shift count
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by calculating (35 - n): if the count is positive, it's a left-shift, and if it's negative, it's a right-shift.
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*n* is always interpreted as a decimal value, regardless of the current base (radix).
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*n* can be converted to a shift count by calculating (35 - n): if the count is positive, it's a left-shift, and if it's negative,
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it's a right-shift. Here are some examples:
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>> print 1B0
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0o400000000000 -34359738368.
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@ -140,7 +142,7 @@ by calculating (35 - n): if the count is positive, it's a left-shift, and if it'
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0o000000000001 1.
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And as the [MACRO-10 Assembler Programmer's Reference Manual (June 1972)](http://archive.pcjs.org/pubs/dec/pdp10/tops10/Macro_Assembler_Reference_Manual-Jun72.pdf),
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p. 1-17, points out, all the following expressions are equivalent:
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p. 1-17, points out, all of the following "binary shifting" expressions are equivalent:
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>> print 10B32
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0o000000000100 64. '@'
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@ -208,5 +210,80 @@ useful in assembling the following tests:
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- [KA10 Basic Instruction Diagnostic #4](/apps/pdp10/diags/klad/dakad/)
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- [Assorted MACRO-10 Mini-Assembler Tests](/apps/pdp10/tests/macro10/)
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However, there's "*assembling*" and then there's "*assembling correctly*". One early problem I had to immediately
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address was the handling of literals. I was originally collecting all the literal (square-bracketed) expressions, like the
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**[ZZ]** in the following statement:
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MOVE [ZZ] ;MOVE THE CURRENT VALUE OF ZZ INTO E. ZZ IS NON-ZERO
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and processing them at the end of the first pass. Well, since ZZ is a symbol that changes repeatedly inside a REPEAT pseudo-op, it
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became clear that I needed to process literals immediately. This meant creating a separate assembly scope while processing each
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literal; in fact, it meant a stack of scopes, in case literals contained nested literals.
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As the [MACRO-10 Assembler Programmer's Reference Manual (April 1978)](http://archive.pcjs.org/pubs/dec/pdp10/tops10/Macro_Assembler_Reference_Manual-Apr78.pdf)
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explains:
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A literal can include any term, symbol, expression, or statement, but
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it must generate at least one but no more than 99 words of data. A
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statement that does not generate data (such as a direct-assignment
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statement or a RADIX pseudo-op) can be included in a literal, but the
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literal must not consist entirely of such statements.
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You can nest literals up to 18 levels. You can include any number of
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labels in a literal, but a forward reference to a label in a literal
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is illegal.
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If you use a dot (.) in a literal to retrieve the location counter,
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remember that the counter is pointing at the statement containing the
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literal, not at the literal itself.
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In nested literals, a dot location counter references a statement
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outside the outermost literal.
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In the sequence:
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JRST [HRRZ AC1,V
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CAIE AC1,OP
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JRST .+1
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JRST EVTSTS]
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SKIPE C
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the expression .+1 generates the address of SKIPE C, not JRST EVTSTS.
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Literals having the same value are collapsed in MACRO's literal pool.
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Thus for the statements:
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PUSH P,[0]
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PUSH P,[0]
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MOVEI AC1,[ASCIZ /TEST1/]
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the same address is shared by the two literals [0], and by the null
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word generated at the end of [ASCIZ /TESTI/]. Literal collapsing is
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suppressed for those literals that contain errors, undefined expressions,
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or EXTERNAL symbols.
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Our Mini-Assembler doesn't enforce all the above requirements. It doesn't care if less than 1 or more
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than 99 words of data are generated, and it doesn't care if you nest more than 18 levels. It does attempt to honor
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MACRO-10's scoping rules for the dot (.) operator, however.
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There's also some ambiguity in the above documentation. For example, it says that a literal may contain "any
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term, symbol, expression, or statement," but it's not clear if that includes labels.
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And when they say that "a forward reference to a label in a literal is illegal," does that only apply to a label
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defined *within* the literal, or to *any* forward reference? In other words, which element is illegal in a literal:
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the forward reference, or the label?
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In any case, our assembler doesn't care, and it's now able to assemble a simple
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[Nested Literal Test](/apps/pdp10/tests/macro10/#nested-literal-test) on the
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[MACRO-10 Mini-Assembler Tests](/apps/pdp10/tests/macro10/) page.
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So, things are improving, but it's still too early expect a lot from the MACRO-10 Mini-Assembler. It currently supports
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only a handful of pseudo-ops, and all the code and data it generates is intended for absolute loading only; for now,
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it makes no distinction between relocatable and absolute addresses, and the **LOC** and **RELOC** pseudo-ops, like every
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other unrecognized or unsupported opcode or pseudo-op, will simply generate an error.
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If that sounds like a joke, it's not. This, however, is:
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> A man walks into a bar, asks the bartender for a fixup, and the bartender responds, "Absolutely!"
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*[@jeffpar](http://twitter.com/jeffpar)*
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*Mar 21, 2017*
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