Questions tagged [assembly]
Assembly languages in general, of any architecture. Use with the particular processor’s tag as appropriate.
151
questions
3
votes
1answer
75 views
What could be the reason an `LD B, B` instruction was used in this busy loop?
The Game Boy game "Tetris" leaves a transmission interval of about a millisecond between bytes sent over the serial link, as suggested by the official Game Boy Programming Manual, to give ...
17
votes
2answers
1k views
Z80 to x86 asm translator?
8086 is source code compatible with 8080. Zilog Z80 extended Intel 8080 with:
An enhanced instruction set including bit manipulation, block move, block I/O, and byte search instructions
New IX and IY ...
4
votes
1answer
83 views
Why have both the ORG and LOC pseudo-operations in the SHARE/Symbolic/Fortran Assembly Programs for the IBM 704/709/7090/7094?
This is a fairly basic question, and I almost feel ashamed to ask it; I'm guessing it can be answered in a single sentence.
There was a rather influential series of assemblers for some of IBM's ...
12
votes
1answer
1k views
Who are the people associated with Simula, Assembler and Fortran in this video?
I am watching a recording of a discussion panel ‘Unix50 - Unix Today and Tomorrow’, part of which contains Bjarne Stroustrup’s talk ‘From C to C++’, discussing the history of C++.
At 20:46 there is a ...
6
votes
3answers
2k views
Z80 string iteration failing
First Z80 project after 6502, a simple looking piece of code giving me hard time.
print_char is a working function which prints contents of A to the screen.
My first issue is that the following code (...
10
votes
0answers
297 views
Assembler where output file was executable WHILE including the source code
I seem to remember using an assembler with the following interesting workflow: You'd write an assembly language file and assemble it. The output overwrote your source code by placing the executable ...
2
votes
2answers
107 views
PDP-1 skip group invert bit functionality
I'm confused on the behavior of setting the invert bit on the PDP-1's SKP group. The manual states:
The intent of any skip instruction can be reversed by making Bit 5 (normally the Indirect Address ...
13
votes
2answers
1k views
Origin of “arithmetic” and “logical” for signed and unsigned shifts
The assembly language for many processors use the phrase "arithmetic shift" to represent the bitwise shift of a signed value, and "logical shift" for an unsigned value. The two ...
4
votes
3answers
180 views
Apple II: ProDOS, zero length prefix and MLI calls
I have a simple program on my Apple IIc written in assembly language. It starts by getting a filename from the user (just the file name, not the full path), then it opens the corresponding file with a ...
12
votes
3answers
2k views
What 8086 instructions accept REP?
I tried this code in my assembler, set to 16 bit mode:
bits 16
rep mov ds, ax
Surprisingly, no error was thrown. Is this even valid? Wasn't rep only supposed to work with string instructions? Is it ...
23
votes
12answers
7k views
Was memory corruption a common problem in large programs written in assembly language?
Memory corruption bugs have always been a common problem in large C programs and projects. It was a problem in 4.3BSD back then, and it's still a problem today. No matter how carefully the program is ...
0
votes
3answers
345 views
How was “Super Mario Bros” made with Assembly if the DASM compiler came out in 1987?
Would somebody care to explain how "Super Mario Bros." was released in 1985. But the DASM Assembler came out in 1987?
The 6502 Assembly language was introduced in 1975. How would you compile/...
4
votes
2answers
410 views
The use of segments in non-relocating assemblers
I've been looking at a bunch of different 6502 assemblers recently (dasm, ca65, xa, kickass), and many of them have support for multiple code segments. Some of these assemblers can generate ...
2
votes
1answer
85 views
Defining zeropage address labels in xa assembler?
I am trying to use the xa assembler to write some 6502 code. According to the documentation, I can define a zeropage segment using the .zero pseudo-op. I was hoping to do something like this:
.zero
...
14
votes
1answer
1k views
How can a Z80 assembly program find out the address stored in the SP register?
I'm wondering how to write a program in Z80 assembler that discovers the value stored in the SP register.
From what I've seen, the only instructions that touch the SP register are:
LD SP, HL/IX/IY
EX ...
9
votes
3answers
981 views
Make the “z80asm” assembler place an instruction at a known memory address
I'm writing a very basic OS for my homebrew Z80 computer. As an absolute assembly language beginner, I managed to obtain a working "os plus memory monitor" that can show memory content and ...
0
votes
3answers
207 views
c64 copy chars to sprite issue
How to do correct copying char to sprite ?
Lets say 1st char is at $2000 second is at $2008 and copying to sprite at $2480.
And with this we can copy 1 char to top left position of 1st sprite. But ...
22
votes
1answer
1k views
When did the IBM 650 have a “Table lookup on Equal” instruction?
In 1959, Donald Knuth wrote an assembly program named SuperSoap for the IBM 650. Here is the manual, and here is a listing of the program (in SuperSoap assembly language). Quoting from the abstract:
...
1
vote
0answers
64 views
Run ca65 assembler with intermediate step of resolving macros
I would like to convert an assembler program in ca65 with macros into assembler code with resolved macros in order to carry out manual or automatic optimizations with the resulting code. Then, the ...
12
votes
2answers
1k views
How would I reliably detect the amount of RAM, including Fast RAM?
If I was to write an Amiga game, what would be the best/most reliable way to detect how much RAM is actually available?
Looking at Action's Guide to AGA-Fixing!, he mentions Faulty Memory Detection:
...
7
votes
2answers
476 views
Labels in cc65 inline assembler with #define macro
In general, it is possible to use inline assembler statements within C macros, for example
#define toscreencode(C) (__AX__ = (C), \
asm("cmp #$60"),\
...
4
votes
3answers
2k views
8086 duration of program
I have the following assembly code for 8086
MOV AL, [BX]
OUT DX, AL
The bus clock frequency is 1MHz. Access to memory is done without WAIT, and to I/O with one WAIT tick. How I can calculate the ...
4
votes
2answers
201 views
Were there “higher level programming” macro packages for the IBM Macro Assembler?
The IBM/360 Macro Assembly language was quite powerful, allowing non-trivial compile-time string manipulation.
Did macro packages exist which would facilitate programming at a (slightly) higher level, ...
12
votes
1answer
757 views
Difference between INT 0x20 and INT 0x21 (0x4C)?
Checking the MS-DOS interrupt list we see INT 0x20 "Terminate the program" (see https://en.wikipedia.org/wiki/DOS_API) but if we check the same page we see INT 0x21 with function 0x4C will &...
5
votes
4answers
414 views
Better way to do Z80 “bank switch & call”?
I have a memory setup where the whole address space can be exchanged (default 2 slots with 2 banks each, but may change depending on "expansion cards" plugged in).
Banks are switched by ...
17
votes
1answer
533 views
Where and when did the “.s” suffix for assembly-language source files originate?
The closest I was able to find on StackOverflow is What are .S files?, in which no answerer addresses why we use .s for assembly. (And .S for preprocessor/macro assembly; and gcc -S to produce ...
6
votes
2answers
401 views
Does a defacto format exist for Commodore 64 SID music?
I first learned about tracker / mod music on my Amiga in the early 1990's. I remember fooling around with Protracker, listening to mods with Intuitracker, and coming to the realization that all those ...
5
votes
1answer
360 views
Why is my program outputting only zeros to the data bus during I/O operations?
I'm building a breadboard Z80-based computer. As now, I have the CPU hooked up to an EEPROM and an I/O device (an HD44780 character display) with appropriate decoding logic.
The ROM chip starts at ...
4
votes
2answers
119 views
6800 I flag at reset
I have written an emulation of the Heathkit ET-3400A microcomputer trainer in Java, mainly to see if I could do it and to get my feet wet in Java. Odd question, but there's a discrepancy (one of many,...
3
votes
2answers
427 views
How were games and programs written for the C64 in assembler in the 80s? [duplicate]
Were developers using monitors like e.g. "Supermon+64", "Merlin 64" or "Monitor$C000" and cartridges like "Final Cartridge", "Action Replay" (both of ...
5
votes
2answers
324 views
Commodore Plus/4 jiffy clock tied to screen refresh frequency? (warning: flashing images)
Warning: There are flashing images below, do not scroll down if you are sensitive to them!
According to various sources (for example this for the Plus/4), both the C64 and Plus/4 have a "jiffy&...
1
vote
1answer
191 views
Working on programming a retro z80 computer (SDCC error)
I am working on coding a driver of sorts for a Z80 based computer I am making. I am compiling with SDCC and I have been getting the following?
ASlink-Warning-Undefined Global 'data' referenced by ...
2
votes
0answers
138 views
Help debugging a circuit/code for Z80 and TMS9918ANL
I am working on designing a Z80 computer that utilized the TMS9918ANL for graphics. I am currently just trying to make sure the TMS9918ANL is working, so I hooked up the control pins the bus (...
10
votes
2answers
739 views
Trying to understand some assembly syntax in the Unix v7 write system call
so here is the code: (which comes from here, I've also verified this source is in my unix v7 distribution). For reference, this is running on a PDP-11 simulated with the simh program (so please keep ...
4
votes
2answers
647 views
Z80 PIO Keyboard [closed]
I am working on designing a Z80 computer and I would like to use a PS/2 Keyboard for input. I would like to use a PIO to communicate with it, but I am having trouble finding any documentation online ...
2
votes
2answers
312 views
How to implement a 'write' function in pdp-11 / MACRO-11 / ODT using simh?
So, I'm working on a project where I'm aiming to get the first winner of the IOCCC (obfuscated c code contest) dissected down to the last detail... The program is mullender.c which you can find by ...
1
vote
1answer
366 views
Using Bresenham's circle algorithm (or another alternative algorithm) to draw an arc [closed]
I'm trying to create some graphics function for a ZX Spectrum (Z80) machine in assembler. I already have the basics except for the arc.
I know that there must be some way to draw an arc using the ...
8
votes
1answer
781 views
On the LR35902, what does the assembly 'LD (HL-),A' do?
I'm working on implementing the instructions of the z80 chip inside a gameboy for an emulator. I'm starting with the instructions in the boot rom that sets everything up.
I've implemented the first 3 ...
34
votes
8answers
8k views
When and why did high-level language compilers start targeting assembly language rather than machine code?
From what I've read, the first FORTRAN compiler built a machine-code program entirely in memory; it was, in fact, designed to read the entire source code of the program, and then sequentially load ...
10
votes
2answers
485 views
How do I tell vasm to allow white spaces?
I have recently been learning to use vasm. For those that don't know, vasm is a cross-platform assembler for multiple types of processors such as the M68000.
http://sun.hasenbraten.de/vasm/
I am ...
11
votes
3answers
445 views
Do any 6502 assemblers have better support for self-modifying code?
I find I keep on doing things like this:
raster_interrupt:
bgnd_color = * + 1
lda #$00
sta $d021
; rest of interrupt handler
so that I can do this kind of thing elsewhere in my ...
1
vote
1answer
376 views
Were all NES games 16 kibibytes or less?
While searching on the Internet and Quora, I found disassemblers for Pac-Man, Galaxian, and Super Mario Bros. The thing that puzzled me, was while Super Mario Bros was arguably quite a complex game ...
17
votes
3answers
3k views
Was there any automated unit testing prior to 1972?
Prior to 1972, was there any automated unit-testing? Did any assemblers include a testing a framework?
I can find some academic journals on this topic from the late 70s -- most of which I don't have ...
34
votes
14answers
8k views
What “unusual” syntax assembly languages are/were there?
This question may have the apparent form of a question soliciting a "list" answer, but I'm expecting the list to be very short, so please bear with me.
What "unusual" syntax assembly languages are/...
7
votes
2answers
797 views
What 6800 assembler to use?
Does anyone know of a good, modern Motorola 6800 assembler?
I've used dasm, which I quite like (and it's even actively developed), but it doesn't actually support 6800. It supports 6803, which is ...
11
votes
1answer
290 views
Inverting the carry flag on an M6800
Are there any tricks that can be used to invert the carry flag on the 6800, in as few bytes as possible?
This is the shortest subroutine I've come up with, which is straight forward:
INVC: BCS ...
3
votes
3answers
479 views
How to transfer the address of a data block into zero page using the Merlin 8 assembler on my Apple //e?
I've been fooling around with the Merlin 8 (v2.58) assembler on my Apple IIe and ran into a small snag.
Basically, I would like to load the address of a block of data into a two-byte pair in zero ...
11
votes
2answers
893 views
Best learning path for Apple IIe assembly language [closed]
I have an emulator up and running and access to the asimov ftp site, and I want to learn how to program assembly language on the Apple IIe. What assembler should I use (Merlin? LISA?) and what book or ...
11
votes
3answers
1k views
How can I access/use memory outside of the standard 1 MB address range of MS-DOS?
How do you access more memory (above the 1MB) in DOS if the 640KB of conventional memory are not enough?
I have read a lot about this, but I couldn't figure out how to do this in actual code. Is ...
6
votes
3answers
431 views
Did the Apollo Guidance Computer or other multi-ROM machines subdivide code between ROM chips/modules to facilitate partial updates?
The Apollo Guidance Computer had its code stored in six modules that held 6 kwords of storage each, and the design of each module was such that changing even a single bit after construction would have ...
