Memory layout of a data structure

From Rosetta Code
Task
Memory layout of a data structure
You are encouraged to solve this task according to the task description, using any language you may know.

It is often useful to control the memory layout of fields in a data structure to match an interface control definition, or to interface with hardware. Define a data structure matching the RS-232 Plug Definition. Use the 9-pin definition for brevity.

Pin Settings for Plug
(Reverse order for socket.)
__________________________________________
1  2  3  4  5  6  7  8  9  10 11 12 13
 14 15 16 17 18 19 20 21 22 23 24 25
_________________
1  2  3  4  5
6  7  8  9
25 pin                        9 pin
1 - PG   Protective ground
2 - TD   Transmitted data     3
3 - RD   Received data        2
4 - RTS  Request to send      7
5 - CTS  Clear to send        8
6 - DSR  Data set ready       6
7 - SG   Signal ground        5
8 - CD   Carrier detect       1
9 - + voltage (testing)
10 - - voltage (testing)
11 -
12 - SCD  Secondary CD
13 - SCS  Secondary CTS
14 - STD  Secondary TD
15 - TC   Transmit clock
16 - SRD  Secondary RD
17 - RC   Receiver clock
18 -
19 - SRS  Secondary RTS            
20 - DTR  Data terminal ready      4
21 - SQD  Signal quality detector
22 - RI   Ring indicator           9
23 - DRS  Data rate select
24 - XTC  External clock
25 -

Ada[edit]

type Bit is mod 2;
type Rs_232_Layout is record
Carrier_Detect  : Bit;
Received_Data  : Bit;
Transmitted_Data  : Bit;
Data_Terminal_ready : Bit;
Signal_Ground  : Bit;
Data_Set_Ready  : Bit;
Request_To_Send  : Bit;
Clear_To_Send  : Bit;
Ring_Indicator  : Bit;
end record;
 
for Rs_232_Layout use record
Carrier_Detect at 0 range 0..0;
Received_Data at 0 range 1..1;
Transmitted_Data at 0 range 2..2;
Data_Terminal_Ready at 0 range 3..3;
Signal_Ground at 0 range 4..4;
Data_Set_Ready at 0 range 5..5;
Request_To_Send at 0 range 6..6;
Clear_To_Send at 0 range 7..7;
Ring_Indicator at 0 range 8..8;
end record;

ALGOL 68[edit]

Works with: ALGOL 68 version Revision 1 - no extensions to language used
Works with: ALGOL 68G version Any - tested with release 1.18.0-9h.tiny
Works with: ELLA ALGOL 68 version Any (with appropriate job cards) - tested with release 1.8-8d
MODE RSTWOTHREETWO = BITS;
INT ofs = bits width - 9;
INT
lwb rs232 = ofs + 1,
carrier detect = ofs + 1,
received data = ofs + 2,
transmitted data = ofs + 3,
data terminal ready = ofs + 4,
signal ground = ofs + 5,
data set ready = ofs + 6,
request to send = ofs + 7,
clear to send = ofs + 8,
ring indicator = ofs + 9,
upb rs232 = ofs + 9;
 
RSTWOTHREETWO rs232 bits := 2r10000000; # up to bits width, OR #
print(("received data: ",received data ELEM rs232bits, new line));
 
rs232 bits := bits pack((FALSE, TRUE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE));
print(("received data: ",received data ELEM rs232bits, new line))

Output:

received data: T
received data: T

C/C++[edit]

Note: The order of the fields is implementation-defined (i.e. the first bit might be the least-significant one or the most-significant one). On GCC and MSVC++, the first bit is the least-significant one.

struct RS232_data
{
unsigned carrier_detect : 1;
unsigned received_data : 1;
unsigned transmitted_data : 1;
unsigned data_terminal_ready : 1;
unsigned signal_ground : 1;
unsigned data_set_ready : 1;
unsigned request_to_send : 1;
unsigned clear_to_send : 1;
unsigned ring_indicator : 1;
};

The ":1" gives the number of allocated bits. For unused bits (e.g. pin 11 in the 25-pin version above) the field name can be omitted.

Since as stated before the order of bits can't be assured but it could be important if we need to interact with hardware, the best way is to define bit masks; of course actual writing/reading to/from an hardware "register" greater than a single byte must be done taking care of endianness.

D[edit]

Tango version[edit]

Implementation uses tango's BitArray structure.

Library: tango
module controlFieldsInStruct;
 
import tango.core.BitArray;
import tango.io.Stdout;
import tango.text.convert.Integer;
 
class RS232Wrapper(int Length = 9)
{
static assert(Length == 9 || Length == 25, "ERROR, wrong type");
BitArray ba;
static uint[char[]] _map;
 
public:
 
static if (Length == 9) {
static this() {
_map = [ cast(char[])
"CD" : 1, "RD" : 2, "TD" : 3, "DTR" : 4, "SG" : 5,
"DSR" : 6, "RTS" : 7, "CTS" : 8, "RI" : 9
];
}
} else {
static this() {
_map = [ cast(char[])
"PG" : 1u, "TD" : 2, "RD" : 3, "RTS" : 4, "CTS" : 5,
"DSR" : 6, "SG" : 7, "CD" : 8, "+" : 9, "-" : 10,
"SCD" : 12, "SCS" : 13, "STD" : 14, "TC" : 15, "SRD" : 16,
"RC" : 17, "SRS" : 19, "DTR" : 20, "SQD" : 21, "RI" : 22,
"DRS" : 23, "XTC" : 24
];
}
}
 
 
this() {
ba.length = Length;
}
 
bool opIndex(uint pos) { return ba[pos]; }
bool opIndexAssign(bool b, uint pos) { return (ba[pos] = b); }
bool opIndex(char[] name) {
assert (name in _map, "don't know that plug: " ~ name);
return opIndex(_map[name]);
}
bool opIndexAssign(bool b, char[] name) {
assert (name in _map, "don't know that plug: " ~ name);
return opIndexAssign(b, _map[name]);
}
void opSliceAssign(bool b) { foreach (ref r; ba) r = b; }
char[] toString() {
char[] ret = "[";
foreach (name, value; _map)
ret ~= name ~ ":" ~ (ba[value]?"1":"0") ~", ";
ret ~= "]";
return ret;
}
}
 
int main(char[][] args)
{
auto ba = new RS232Wrapper!(25);
 
// set all bits
ba[] = 1;
ba["RD"] = 0;
ba[5] = 0;
 
Stdout (ba).newline;
 
return 0;
}

Output:

[RD:0, RI:1, DSR:1, SG:1, DTR:1, TC:1, TD:1, CD:1, SQD:1, +:1, -:1, SRD:1, RTS:1, SRS:1, STD:1, PG:1, SCD:1, CTS:0, DRS:1, SCS:1, XTC:1, RC:1 ]

Phobos version[edit]

Not tested.

import std.bitmanip;
 
struct RS232_data {
static if (std.system.endian == std.system.Endian.bigEndian) {
mixin(bitfields!(bool, "carrier_detect", 1,
bool, "received_data", 1,
bool, "transmitted_data", 1,
bool, "data_terminal_ready", 1,
bool, "signal_ground", 1,
bool, "data_set_ready", 1,
bool, "request_to_send", 1,
bool, "clear_to_send", 1,
bool, "ring_indicator", 1,
bool, "", 7));
} else {
mixin(bitfields!(bool, "", 7,
bool, "ring_indicator", 1,
bool, "clear_to_send", 1,
bool, "request_to_send", 1,
bool, "data_set_ready", 1,
bool, "signal_ground", 1,
bool, "data_terminal_ready", 1,
bool, "transmitted_data", 1,
bool, "received_data", 1,
bool, "carrier_detect", 1));
}
 
static assert(RS232_data.sizeof == 2);
}
 
void main() {}

Forth[edit]

Low level hardware control is a typical use of Forth. None of this is standard, however, since hardware I/O mechanisms differ on different systems. Forth does not have a structure mechanism, much less bitfields. These would be represented instead via bitmask constants if doing real serial port control.

 : masks ( n -- ) 0 do 1 i lshift constant loop ;
 
9 masks DCD RxD TxD DTR SG DSR RTS CTS RI

Example usage, assuming I/O primitives in and out:

 hex
3fd constant com1-ctrl
decimal
 
 : wait-ready
begin
com1-ctrl in
CTS and
until ;
 : wait-rx
begin
com1-ctrl in
CTS and 0=
until ;
 
 : send-byte ( b -- ) \ send assuming N81 (no parity, 8 bits data, 1 bit frame)
255 and
9 0 do
RTS com1-ctrl out
wait-ready
dup 1 and if TxD else 0 then com1-ctrl out
wait-rx
2/
loop drop ;

Of course, this is a very simplified view of the full RS-232 protocol. Also, although this represents the order of the pins in a D-9 connector, this would not necessarily be the same as the order of the bits in a control register.

Fortran[edit]

Modern[edit]

F90 introduced the ability to define compound data aggregates, as had been used from the start by COBOL in the 1960s. Thus, one could define
       TYPE RS232PIN9
LOGICAL CARRIER_DETECT !1
LOGICAL RECEIVED_DATA !2
LOGICAL TRANSMITTED_DATA !3
LOGICAL DATA_TERMINAL_READY !4
LOGICAL SIGNAL_GROUND !5
LOGICAL DATA_SET_READY !6
LOGICAL REQUEST_TO_SEND !7
LOGICAL CLEAR_TO_SEND !8
LOGICAL RING_INDICATOR !9
END TYPE RS232PIN9

But it would be nearly pointless to do so.

Fortran's LOGICAL type is defined to occupy as much space as the default INTEGER type, which is typically thirty-two bits. This was done to simplify questions of storage size for large collections of assorted types of variables in a COMMON storage area. Further, true and false may not be signified by 1 and 0 but by -1 and 0, or, something else. Many compilers continue to support the old-style storage size indications that were introduced for binary computers and so would allow LOGICAL*1, but alas, this does not mean one bit, it means one byte. There is no equivalent of a key word PACKED (as in Pascal for example) whereby it might be indicated that a collection of items are to be stored "adjacent" and not aligned to byte or word boundaries. But, without a storage type equivalent to BIT(1) such as pl/i offers, this won't help either. Such packing can make reading or writing to a variable quite difficult - imagine a 32-bit integer variable offset by three bits - which is why some languages offer the keyword ALIGNED.

However, all is not quite lost. Given that one can access the special storage word containing the status of the nine-pin socket, presumably returning what can be regarded as a thirty-two bit integer (to accommodate a 25-pin socket), then, given certain knowledge of the ordering of the pins versus the bits of the integer (are bits counted from left-to-right or right-to-left, starting at one or at zero?), and certain knowledge that the nine bits are at the high-order end of the word or at the low-order end of the word (the IBM 1130's card reader placed the image of a column of a card, twelve bits, at the high-order end of its sixteen-bit word), it would be merely a matter of tedium to unpack those bits with suitable expressions and place the appropriate values into the components of a variable of type RS232PIN9. Such variables can then be juggled in the usual way, for instance using NAMELIST style I/O whereby the values are presented along with the names of the variables holding them. For output, this could be achieved with suitable FORMAT statements.

There may be available library functions IAND(i,j) and IOR(i,j) for dealing with integer variables, otherwise it becomes a matter of integer arithmetic. Unpacking or re-packing a data structure (say, as found in a disc file record) is straightforward but tedious, and, aside from the sizes and types of the components one must have definite knowledge of the endianness of the data as in the aggregate (read from disc) compared to the endianness of the cpu running your procedure. Easiest is of course to have the same style cpu for both.

Older style[edit]

Without the ability to create data aggregates via TYPE statements, whereby a single variable might sprawl across memory as above, one instead prepared a collection of variables, usually with some systematic name convention linking the names of the parts. These variables would be anywhere in memory and so had no particular memory layout in themselves. However, when stored as a record in a disc file a data structure is created with a definite layout, and this is manifest in the READ and WRITE statements involved. Suppose the statement was WRITE (F,REC = n) THIS,M,NAME meaning that the n'th record of file unit F was to be written. The types of the variables would be known, and their sizes also. Say REAL*8 THIS, INTEGER*1 M, and CHARACTER*28 NAME. Such a record could be read (or written) by READ (F,REC = n) STUFF given a declaration CHARACTER*37 STUFF (counting on fingers as necessary) and the various parts of the data aggregate could be indexed within STUFF. However, the interpretation of the interior bytes of multi-byte items such as integer and floating-point variables is complicated by the endianness of the processor, a confounding nuisance.

It is further possible to declare that STUFF is to occupy the same storage as the named variables. If the declaration was CHARACTER*1 STUFF(37), then EQUIVALENCE (STUFF(1),THIS),(STUFF(9),M),(STUFF(10),NAME) would mean that STUFF occupied the same storage as those variables, or rather, that the variables occupied the same storage as STUFF - indeed, they could overlay each other, which would be unlikely to be helpful. This could mean that a floating-point or integer variable was not aligned to a word boundary with the consequent penalty in access, for instance by having THIS start with STUFF(2) because M was put first. Some systems may not allow byte-based addressing, only word-based so complications can arise. But this demonstrates precise knowledge of the memory layout of a data structure. The more modern compilers that allow the TYPE declaration typically do not allow the appearance of such variables in EQUIVALENCE statements, to prevent access to the memory layout of such data structures. Others allow a new version of EQUIVALENCE (which the moderns deprecate) via the MAP statement, but this is not standard Fortran.

As before stated, there is no BIT facility, so packing is to byte boundaries. But, if one is determined to store thousands of records with minimal storage use, it may seem worth the effort to engage in the arithmetic to pack the likes of say three bits, followed by the thirty-two bits of a floating-point value, and so on, into a sequence of bytes which then would be written. In such a situation it may even be worth packing only a portion of the floating-point variable, if reduced precision is acceptable and one is certain of the usage of the bits within such a number. However, given the difficulty of access to the parts of such a packed aggregate, it is usually better to leave the byte/word packing and unpacking to the I/O system as via WRITE (F,REC = n) THIS,M,NAME and then manipulate the variables as their conveniently-aligned in-memory forms as ordinary variables, only repacking to the data structure form with a subsequent WRITE statement.

The INTEGER*n opportunity is not fully flexible in that powers of two are usually the only options so that a value that might fit into INTEGER*3 will have to go into INTEGER*4. In any case this style is not helpful for decimal machines or binary computers whose word size is not a power of two. It is possible to break away from a byte base, especially when there are many variables with small ranges to represent. Suppose that V3 only has values 0, 1, 2; V5 has only 0, 1, 2, 3, 4; V4 only 0, 1, 2, 3; and V2 only 0, 1. Then a set of values could be encoded as a single decimal number: say 1230 for the four variables in that order, which would fit into a two byte integer instead of four one byte integers. That is merely changing base 256 to base 10, notionally, but a better packing is possible, Consider V = V3 + 3*(V5 + 5*(V4 + 4*(V2))) whose maximum value would be 2 + 3*(4 + 5*(3 + 4*1)) = 119, which will fit into one byte. If there were many such variables, then their packed values might require larger integers for even greater sharing. Variables with fractional values can be treated in a similar way, cautiously...

With careful planning, such a compound value may even have helpful numerical properties, of service for (some) multi-key sorts. In the example, V2 is the high-order value so if a desired sort key happened to include V2, V4, V5, V3 then a four-variable comparison could be done in just one test. Unless the value overflows into the sign bit. This may not be a problem if the sorted order is merely to facilitate a binary search that will use the same ordering, but there can still be surprises. The B6700 used a 48-bit word and its compiler did not offer the then-unknown CHARACTER type. One might store six eight-bit characters in a word without worrying over the ordering that will result - the B6700 had no integer representation as such, using floating-point numbers with no fractional part, so the numerical values resulting from character codes would be quite odd. However, it also worked in base eight and although forty-eight is divisible by three, the requirement for the sign of the exponent and the sign of the value uses only two bits. Thus, one bit, the topmost, did not participate in arithmetic operations and as a result, arithmetic could not distinguish between characters in the high end of a word that differed in their highest bit. Even .EQ. would fail and the compiler offered a special substitute, .IS. to test for equality. Other languages that offered character manipulation (such as the extensions to Algol) used entirely different methods that avoided this problem.

In a similar way, text content may employ only a limited character set so perhaps five bits per symbol would suffice, or some other packing scheme might suggest itself. There is also a whole world of compression algorithms. The end result is that a data structure manifesting as records in a disc file may be difficult to unpack into a convenient internal form even given a careful description of the layout.

FreeBASIC[edit]

' FB 1.05.0 Win64
 
' using bit fields
Type RS232_Pin9
carrierDetect  : 1 As UByte
receivedData  : 1 As UByte
transmittedData  : 1 As UByte
dataTerminalReady : 1 As UByte
signalGround  : 1 As UByte
dataSetReady  : 1 As UByte
requestToSend  : 1 As UByte
clearToSend  : 1 As UByte
ringIndicator  : 1 As UByte
End Type
 
Print SizeOf(RS232_Pin9) '' 2 bytes
Sleep

Go[edit]

Go does not have named bits as part of the type system. Instead, constants are typically defined as shown. For a word of bits with special meanings like this, a type would be defined though, as shown. Static typing rules then control assignments and comparisons at the word level. At the bit level, it helps to follow naming conventions so that, say, using a 9-pin constant on a 25-pin word would be an obvious error in the source code.

package main
 
import "fmt"
 
type rs232p9 uint16
 
const (
CD9 rs232p9 = 1 << iota // Carrier detect
RD9 // Received data
TD9 // Transmitted data
DTR9 // Data terminal ready
SG9 // signal ground
DSR9 // Data set ready
RTS9 // Request to send
CTS9 // Clear to send
RI9 // Ring indicator
)
 
func main() {
// set some nonsense bits just for example
p := RI9 | TD9 | CD9
fmt.Printf("Type=%T value=%#04x\n", p, p)
}
Output:
Type=main.rs232p9 value=0x0105

J[edit]

J does not support "structures", nor "fields in a structure". Instead, J supports arrays. And, of course, J could have labels corresponding to the elements of an array representing the state (voltage, current, logical bit value, whatever) of each pin of a 9-pin RS-232 plug:

labels=: <;._2]0 :0
CD Carrier detect
RD Received data
TD Transmitted data
DTR Data terminal ready
SG Signal ground
DSR Data set ready
RTS Request to send
CTS Clear to send
RI Ring indicator
)

Kotlin[edit]

If it were only desired to access pin settings by position (albeit starting from pin 0 rather than pin 1), then a java.util.BitSet could be used to model this task.

However, if access by both position and name is required, then a data class with 9 named boolean properties would be more suitable. This automatically generates functions called component1, component2 etc. to get the pin values by pin number. However, a function needs to be written manually to set pin values by pin number:

// version 1.0.6
 
const val OFF = false
const val ON = true
 
fun toOnOff(b: Boolean) = if (b) "ON" else "OFF"
 
data class Rs232Pins9(
var carrierDetect : Boolean = OFF,
var receivedData : Boolean = OFF,
var transmittedData : Boolean = OFF,
var dataTerminalReady : Boolean = OFF,
var signalGround : Boolean = OFF,
var dataSetReady : Boolean = OFF,
var requestToSend : Boolean = OFF,
var clearToSend : Boolean = OFF,
var ringIndicator : Boolean = OFF
) {
fun setPin(n: Int, v: Boolean) {
when (n) {
1 -> carrierDetect = v
2 -> receivedData = v
3 -> transmittedData = v
4 -> dataTerminalReady = v
5 -> signalGround = v
6 -> dataSetReady = v
7 -> requestToSend = v
8 -> clearToSend = v
9 -> ringIndicator = v
}
}
}
 
fun main(args: Array<String>) {
val plug = Rs232Pins9(carrierDetect = ON, receivedData = ON) // set first two pins, say
println(toOnOff(plug.component2())) // print value of pin 2 by number
plug.transmittedData = ON // set pin 3 by name
plug.setPin(4, ON) // set pin 4 by number
println(toOnOff(plug.component3())) // print value of pin 3 by number
println(toOnOff(plug.dataTerminalReady)) // print value of pin 4 by name
println(toOnOff(plug.ringIndicator)) // print value of pin 9 by name
}
Output:
ON
ON
ON
OFF

MATLAB / Octave[edit]

Defining structs in MATLAB is kind of bulky, making a class definition might be cleaner for this purpose. If you need to enumerate each pin rather than set the state of the pin using the name of the pin, you can use struct2cell() on the rs232 struct, which will return a cell array whose entries are the value of each of the structs fields in the order in which they were defined.

>> rs232 = struct('carrier_detect', logical(1),...
'received_data' , logical(1), ...
'transmitted_data', logical(1),...
'data_terminal_ready', logical(1),...
'signal_ground', logical(1),...
'data_set_ready', logical(1),...
'request_to_send', logical(1),...
'clear_to_send', logical(1),...
'ring_indicator', logical(1))
 
rs232 =
 
carrier_detect: 1
received_data: 1
transmitted_data: 1
data_terminal_ready: 1
signal_ground: 1
data_set_ready: 1
request_to_send: 1
clear_to_send: 1
ring_indicator: 1
 
>> struct2cell(rs232)
 
ans =
 
[1]
[1]
[1]
[1]
[1]
[1]
[1]
[1]
[1]

Mercury[edit]

Mercury does not have data types that mark down to individual bits. Instead it allows you to use symbolic names (as per the rs232_pin type definition below with its constructors like carrier_detect) and to easily map those names to a value if you so choose (as per the to_index/1 function below).

This is, admittedly, more verbose than the equivalent code would be in, say, C, but it permits things which are more difficult to pull off in such languages. First, the code here is perfectly type safe (despite the use of unsafe_set and unsafe_clear). It is literally impossible to set or clear bits outside of the bounds of the bit array used in the physical representation. It is as easy to set and clear individual bits in the bit array as it is to use bit notation in C, and it's easier to do than when using the safer "integer variable with bitwise operators" technique. Setting and clearing groups of bits is even easier via the rs232_set_bits/2 function: merely pass in a list of symbolic names. Changing the bitwise representation is a matter of changing the bit numbers in to_index/1 and possibly changing the size of the bit array in rs232_bits/1. Indeed the entire underlying representation and implementation can change without the interface changing at all.

Aiding in changing the underlying representation at will is the fact that the exposed type—rs232— is an opaque data type. Instead of exposing the fact of the bitmap implementation to the outside world, it is carefully concealed by the implementation. It is impossible for any code using this module to operate on the underlying bitmap with anything other than the API which has been exposed. This means that should it be deemed desirable to instead use an int as the underlying representation, this can be done without changing even one byte of client code.

rs232.m[edit]

 
:- module rs232.
 
:- interface.
 
:- import_module bool, io, list, string.
 
:- type rs232_pin
---> carrier_detect
 ; received_data
 ; transmitted_data
 ; data_terminal_ready
 ; signal_ground
 ; data_set_ready
 ; request_to_send
 ; clear_to_send
 ; ring_indicator.
 
:- type rs232.
 
:- func rs232_bits = rs232.
:- func rs232_bits(bool) = rs232.
 
:- func rs232_set(rs232, rs232_pin) = rs232.
:- func rs232_clear(rs232, rs232_pin) = rs232.
 
:- pred rs232_is_set(rs232::in, rs232_pin::in) is semidet.
:- pred rs232_is_clear(rs232::in, rs232_pin::in) is semidet.
 
:- func rs232_set_bits(rs232, list(rs232_pin)) = rs232.
:- func rs232_clear_bits(rs232, list(rs232_pin)) = rs232.
 
:- func to_string(rs232) = string.
 
:- pred write_rs232(rs232::in, io::di, io::uo) is det.
 
:- implementation.
 
:- import_module bitmap.
 
:- type rs232 == bitmap.
 
rs232_bits = rs232_bits(no).
rs232_bits(Default) = bitmap.init(9, Default).
 
rs232_set(A, Pin) = unsafe_set(A, to_index(Pin)).
rs232_clear(A, Pin) = unsafe_clear(A, to_index(Pin)).
 
rs232_is_set(A, Pin)  :- unsafe_is_set(A, to_index(Pin)).
rs232_is_clear(A, Pin) :- unsafe_is_clear(A, to_index(Pin)).
 
rs232_set_bits(A, Pins) = foldl((func(Pin, B) = rs232_set(B, Pin)), Pins, A).
rs232_clear_bits(A, Pins) = foldl((func(Pin, B) = rs232_clear(B, Pin)), Pins, A).
 
to_string(A) = bitmap.to_string(A).
 
write_rs232(A, !IO) :- write_bitmap(resize(A, 16, no), !IO).
 % cannot write a bitmap that isn't byte-divisible
 
:- func to_index(rs232_pin) = bit_index.
to_index(carrier_detect) = 0.
to_index(received_data) = 1.
to_index(transmitted_data) = 2.
to_index(data_terminal_ready) = 3.
to_index(signal_ground) = 4.
to_index(data_set_ready) = 5.
to_index(request_to_send) = 6.
to_index(clear_to_send) = 7.
to_index(ring_indicator) = 8.
 
:- end_module rs232.
 

rs232_main.m[edit]

:- module rs232_main.
 
:- interface.
 
:- import_module io.
 
:- pred main(io::di, io::uo) is det.
 
:- implementation.
 
:- import_module bitmap, bool, list, rs232.
 
main(!IO) :-
Com1 = rs232_set_bits(rs232_bits, [data_terminal_ready, data_set_ready]),
Com2 = rs232_clear_bits(rs232_bits(yes), [data_terminal_ready, data_set_ready]),
 
write_string("Com1 bits = ", !IO),
write_string(to_string(Com1), !IO), nl(!IO),
 
write_string("Com2 bits = ", !IO),
write_string(to_string(Com2), !IO), nl(!IO),
 
write_string("Com1 DTR is ", !IO),
( if rs232_is_set(Com1, data_terminal_ready) then
write_string("set.", !IO), nl(!IO)
else
write_string("clear.", !IO), nl(!IO)
),
 
write_string("Com2 DSR is ", !IO),
( if rs232_is_clear(Com2, data_set_ready) then
write_string("clear.", !IO), nl(!IO)
else
write_string("set.", !IO), nl(!IO)
).
 
:- end_module rs232_main.
 

Usage and output[edit]

 $ mmc --make rs232_main
 $ ./rs232_main
 Com1 bits = <9:1400>
 Com2 bits = <9:EB80>
 Com1 DTR is set.
 Com2 DSR is clear.

Nim[edit]

type
rs232Data = enum
carrierDetect,
receivedData,
transmittedData,
dataTerminalReady,
signalGround,
dataSetReady,
requestToSend,
clearToSend,
ringIndicator
 
# Bit vector of 9 bits
var bv = {carrierDetect, signalGround, ringIndicator}
echo cast[uint16](bv) # Conversion of bitvector to 2 bytes for writing
 
let readValue: uint16 = 123
bv = cast[set[rs232Data]](readValue) # Conversion of a read value to bitvector
echo bv

Output:

273
{carrierDetect, receivedData, dataTerminalReady, signalGround, dataSetReady, requestToSend}

OCaml[edit]

Library: extlib

open ExtLib
class rs232_data = object
val d = BitSet.create 9
 
method carrier_detect = BitSet.is_set d 0
method received_data = BitSet.is_set d 1
method transmitted_data = BitSet.is_set d 2
method data_terminal_ready = BitSet.is_set d 3
method signal_ground = BitSet.is_set d 4
method data_set_ready = BitSet.is_set d 5
method request_to_send = BitSet.is_set d 6
method clear_to_send = BitSet.is_set d 7
method ring_indicator = BitSet.is_set d 8
 
method set_carrier_detect b = (if b then BitSet.set else BitSet.unset) d 0
method set_received_data b = (if b then BitSet.set else BitSet.unset) d 1
method set_transmitted_data b = (if b then BitSet.set else BitSet.unset) d 2
method set_data_terminal_ready b = (if b then BitSet.set else BitSet.unset) d 3
method set_signal_ground b = (if b then BitSet.set else BitSet.unset) d 4
method set_data_set_ready b = (if b then BitSet.set else BitSet.unset) d 5
method set_request_to_send b = (if b then BitSet.set else BitSet.unset) d 6
method set_clear_to_send b = (if b then BitSet.set else BitSet.unset) d 7
method set_ring_indicator b = (if b then BitSet.set else BitSet.unset) d 8
end
;;

Pascal[edit]

Works with: Free_Pascal
program memoryLayout;
 
type
T_RS232 = (
carrier_detect,
received_data,
transmitted_data,
data_terminal_ready,
signal_ground,
data_set_ready,
request_to_send,
clear_to_send,
ring_indicator
);
 
var
Signal: bitpacked array[T_RS232] of boolean;
 
begin
Signal[signal_ground] := true;
end.

Perl[edit]

use Bit::Vector::Minimal qw();
my $vec = Bit::Vector::Minimal->new(size => 24);
 
my %rs232 = reverse (
1 => 'PG Protective ground',
2 => 'TD Transmitted data',
3 => 'RD Received data',
4 => 'RTS Request to send',
5 => 'CTS Clear to send',
6 => 'DSR Data set ready',
7 => 'SG Signal ground',
8 => 'CD Carrier detect',
9 => '+ voltage (testing)',
10 => '- voltage (testing)',
12 => 'SCD Secondary CD',
13 => 'SCS Secondary CTS',
14 => 'STD Secondary TD',
15 => 'TC Transmit clock',
16 => 'SRD Secondary RD',
17 => 'RC Receiver clock',
19 => 'SRS Secondary RTS',
20 => 'DTR Data terminal ready',
21 => 'SQD Signal quality detector',
22 => 'RI Ring indicator',
23 => 'DRS Data rate select',
24 => 'XTC External clock',
);
 
$vec->set($rs232{'RD Received data'}, 1);
$vec->get($rs232{'TC Transmit clock'});

Perl 6[edit]

Translation of: Pascal

The following is specced to work, but implementation of shaped arrays is not quite complete.

enum T_RS232 <
carrier_detect
received_data
transmitted_data
data_terminal_ready
signal_ground
data_set_ready
request_to_send
clear_to_send
ring_indicator
>;
 
my bit @signal[T_RS232];
 
@signal[signal_ground] = 1;

In the absence of shaped arrays, you can do the usual bit-twiddling tricks on a native integer of sufficient size. (Such an integer could presumably be mapped directly to a device register.)

$signal +|= 1 +< signal_ground;

Using a native int is likelier to work on a big-endian machine in any case. Another almost-there solution is the mapping of C representational types into Perl 6 for native interfaces, but it does not yet support bit fields.

Phix[edit]

Phix does not support bit-fields directly. The nearest/sanest thing to do probably goes something like this (completely untested)

constant CD=1, RD=2, TD=3, DTR=4, ...
atom addr = allocate(2) -- or wherever
--read
sequence bits = int_to_bits(peek2u(addr),16)
integer dtr = bits[DTR]
--write
bits[DTR] = 1
poke2(addr,bits_to_int(bits))

Naturally, you would be well advised to sequester such grubby details away in a small and separate unit/source code file (eg RS232.e) with a domain specific public API that does not leak implementation details (eg keep those constants private). There are 1/2/4/8 byte variants of peek and poke, and int-to-bits can extract anything from 1 to 53 bits on a 32-bit runtime, or up to 64 on a 64-bit runtime. Alternatively you could use bit-masks, or it may be possible to enhance builtins/cffi.e to manage bit-fields, then again the above C entry does not exactly inspire confidence.

PicoLisp[edit]

PicoLisp can handle bit fields or bit structures only as bignums. They can be manipulated with '&', '|' and 'x|', or tested with 'bit?'.

# Define bit constants
(for (N . Mask) '(CD RD TD DTR SG DSR RTS CTS RI)
(def Mask (>> (- 1 N) 1)) )
 
# Test if Clear to send
(when (bit? CTS Data)
... )

PL/I[edit]

 
declare 1 RS232_layout,
2 Carrier_Detect Bit(1),
2 Received_Data Bit(1),
2 Transmitted_Data Bit(1),
2 Data_Terminal_ready Bit(1),
2 Signal_Ground Bit(1),
2 Data_Set_Ready Bit(1),
2 Request_To_Send Bit(1),
2 Clear_To_Send Bit(1),
2 Ring_Indicator Bit(1);
 

Python[edit]

The ctypes module allows for the creation of Structures that can map between the structures of C and python datatypes. Within Structures, bit fields can be created.

from ctypes import Structure, c_int
 
rs232_9pin = "_0 CD RD TD DTR SG DSR RTS CTS RI".split()
rs232_25pin = ( "_0 PG TD RD RTS CTS DSR SG CD pos neg"
"_11 SCD SCS STD TC SRD RC"
"_18 SRS DTR SQD RI DRS XTC" ).split()
 
class RS232_9pin(Structure):
_fields_ = [(__, c_int, 1) for __ in rs232_9pin]
 
 
class RS232_25pin(Structure):
_fields_ = [(__, c_int, 1) for __ in rs232_25pin]

Racket[edit]

 
#lang racket
 
(require ffi/unsafe)
 
(define (_autobitmask l)
(_bitmask (append* (for/list ([x l] [i (in-naturals)]) `(,x = ,(expt 2 i))))))
 
(define _rs232 (_autobitmask '(CD RD TD DTR SG DSR RTS CTS RI )))
 
;; Usually it will get used when using foreign functions automatically, but
;; this demonstrates the conversions explicitly
(require (only-in '#%foreign ctype-scheme->c ctype-c->scheme))
((ctype-scheme->c _rs232) '(SG TD RI)) ; -> 276
((ctype-c->scheme _rs232) 276)  ; -> '(TD SG RI)
 

REXX[edit]

version 1[edit]

/* REXX ***************************************************************
* Decode Memory structure of RS-232 Plug Definition
* Not sure if I understood it completely :-) Open for corrections
* You never stop learning (as long as you live)
* 03.08.2012 Walter Pachl
**********************************************************************/

Call decode 'ABC'
Call decode 'XY'
Exit
 
decode:
Parse Arg c
cb=c2b(c)
If length(cb)=24 Then Do
Parse Var cb,
/* 1 - PG */ Protective ground +1,
/* 3 2 - TD */ Transmitted_data +1,
/* 2 3 - RD */ Received_data +1,
/* 7 4 - RTS */ Request_to_send +1,
/* 8 5 - CTS */ Clear_to_send +1,
/* 6 6 - DSR */ Data_set_ready +1,
/* 5 7 - SG */ Signal_ground +1,
/* 1 8 - CD */ Carrier_detect +1,
/* 9 - + */ plus_voltage +1,
/* 10 - - */ minus_voltage +1,
/* 11 - */ . +1,
/* 12 - SCD */ Secondary_CD +1,
/* 13 - SCS */ Secondary_CTS +1,
/* 14 - STD */ Secondary_TD +1,
/* 15 - TC */ Transmit_clock +1,
/* 16 - SRD */ Secondary_RD +1,
/* 17 - RC */ Receiver_clock +1,
/* 18 - */ . +1,
/* 19 - SRS */ Secondary_RTS +1,
/* 4 20 - DTR */ Data_terminal_ready +1,
/* 21 - SQD */ Signal_quality_detector+1,
/* 9 22 - RI */ Ring_indicator +1,
/* 23 - DRS */ Data_rate_select +1,
/* 24 - XTC */ External_clock +1
Say '24 bins:' cb
Say ' 1 - PG Protective ground ='Protective ground
Say ' 2 - TD Transmitted data ='Transmitted_data
Say ' 3 - RD Received data ='Received_data
Say ' 4 - RTS Request to send ='Request_to_send
Say ' 5 - CTS Clear to send ='Clear_to_send
Say ' 6 - DSR Data set ready ='Data_set_ready
Say ' 7 - SG Signal ground ='Signal_ground
Say ' 8 - CD Carrier detect ='Carrier_detect
Say ' 9 - + plus voltage ='plus_voltage
Say '10 - - minus voltage ='minus_voltage
Say ' '
Say '12 - SCD Secondary CD ='Secondary_CD
Say '13 - SCS Secondary CTS ='Secondary_CTS
Say '14 - STD Secondary TD ='Secondary_TD
Say '15 - TC Transmit clock ='Transmit_clock
Say '16 - SRD Secondary RD ='Secondary_RD
Say '17 - RC Receiver clock ='Receiver_clock
Say ' '
Say '19 - SRS Secondary RTS ='Secondary_RTS
Say '20 - DTR Data terminal ready ='Data_terminal_ready
Say '21 - SQD Signal quality detector ='Signal_quality_detector
Say '22 - RI Ring indicator ='Ring_indicator
Say '23 - DRS Data rate select ='Data_rate_select
Say '24 - XTC External hlock ='External_clock
End
Else Do
Parse Var cb,
/* 1 8 - CD */ Carrier_detect +1,
/* 2 3 - RD */ Received_data +1,
/* 3 2 - TD */ Transmitted_data +1,
/* 4 20 - DTR */ Data_terminal_ready +1,
/* 5 7 - SG */ Signal_ground +1,
/* 6 6 - DSR */ Data_set_ready +1,
/* 7 4 - RTS */ Request_to_send +1,
/* 8 5 - CTS */ Clear_to_send +1,
/* 9 22 - RI */ Ring_indicator +1
Say ' '
Say '9-bin:' left(cb,9)
Say ' 1 CD Carrier detect ='Carrier_detect
Say ' 2 RD Received data ='Received_data
Say ' 3 TD Transmitted data ='Transmitted_data
Say ' 4 DTR Data terminal ready ='Data_terminal_ready
Say ' 5 SG Signal ground ='Signal_ground
Say ' 6 DSR Data set ready ='Data_set_ready
Say ' 7 RTS Request to send ='Request_to_send
Say ' 8 CTS Clear to send ='Clear_to_send
Say ' 9 RI Ring indicator ='Ring_indicator
End
Return
c2b: Procedure
/* REXX ***************************************************************
* c2b Convert a character string to a bit string
* 03.08.2012 Walter Pachl
**********************************************************************/

Parse Arg c
x=c2x(c)
res=''
Do While x<>''
Parse Var x hb +1 x
Select
When hb='0' Then bs='0000'
When hb='1' Then bs='0001'
When hb='2' Then bs='0010'
When hb='3' Then bs='0011'
When hb='4' Then bs='0100'
When hb='5' Then bs='0101'
When hb='6' Then bs='0110'
When hb='7' Then bs='0111'
When hb='8' Then bs='1000'
When hb='9' Then bs='1001'
When hb='A' Then bs='1010'
When hb='B' Then bs='1011'
When hb='C' Then bs='1100'
When hb='D' Then bs='1101'
When hb='E' Then bs='1110'
When hb='F' Then bs='1111'
End
res=res||bs
End
Return res

Output EBCDIC:

24 bins: 110000011100001011000011
 1 - PG  Protective ground       =1
 2 - TD  Transmitted data        =1
 3 - RD  Received data           =0
 4 - RTS Request to send         =0
 5 - CTS Clear to send           =0
 6 - DSR Data set ready          =0
 7 - SG  Signal ground           =0
 8 - CD  Carrier detect          =1
 9 - +   plus voltage            =1
10 - -   minus voltage           =1

12 - SCD Secondary CD            =0
13 - SCS Secondary CTS           =0
14 - STD Secondary TD            =0
15 - TC  Transmit clock          =1
16 - SRD Secondary RD            =0
17 - RC  Receiver clock          =1

19 - SRS Secondary RTS           =0
20 - DTR Data terminal ready     =0
21 - SQD Signal quality detector =0
22 - RI  Ring indicator          =0
23 - DRS Data rate select        =1
24 - XTC External hlock          =1

9-bin: 111001111
 1 CD   Carrier detect      =1
 2 RD   Received data       =1
 3 TD   Transmitted data    =1
 4 DTR  Data terminal ready =0
 5 SG   Signal ground       =0
 6 DSR  Data set ready      =1
 7 RTS  Request to send     =1
 8 CTS  Clear to send       =1
 9 RI   Ring indicator      =1

version 2[edit]

Checks could be added to verify the number of pins selected, and also verify if the data (pin readings) specified is valid.

/*REXX program  displays  which  pins  are active of a  9  or  24  pin  RS-232  plug.   */
call rs_232 24, 127 /*the value for an RS-232 24 pin plug.*/
call rs_232 24, '020304x' /* " " " " " " " " */
call rs_232 9, '10100000b' /* " " " " " 9 " " */
exit /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
rs_232: arg ,x; parse arg pins,ox /*X is uppercased when using ARG. */
@. = '??? unassigned pin' /*assign a default for all the pins. */
@.24.1 = 'PG protective ground'
@.24.2 = 'TD transmitted data'  ; @.9.3 = @.24.2
@.24.3 = 'RD received data'  ; @.9.2 = @.24.3
@.24.4 = 'RTS request to send'  ; @.9.7 = @.24.4
@.24.5 = 'CTS clear to send'  ; @.9.8 = @.24.5
@.24.6 = 'DSR data set ready'  ; @.9.6 = @.24.6
@.24.7 = 'SG signal ground'  ; @.9.5 = @.24.7
@.24.8 = 'CD carrier detect'  ; @.9.1 = @.24.8
@.24.9 = '+ positive voltage'
@.24.10 = '- negative voltage'
@.24.12 = 'SCD secondary CD'
@.24.13 = 'SCS secondary CTS'
@.24.14 = 'STD secondary td'
@.24.15 = 'TC transmit clock'
@.24.16 = 'SRD secondary RD'
@.24.17 = 'RC receiver clock'
@.24.19 = 'SRS secondary RTS'
@.24.20 = 'DTR data terminal ready'  ; @.9.4 = @.24.20
@.24.21 = 'SQD signal quality detector'
@.24.22 = 'RI ring indicator'  ; @.9.9 = @.24.22
@.24.23 = 'DRS data rate select'
@.24.24 = 'XTC external clock'
 
select
when right(x, 1)=='B' then bits= strip(x, 'T', "B")
when right(x, 1)=='X' then bits=x2b(strip(x, 'T', "X"))
otherwise bits=x2b( d2x(x) )
end /*select*/
say
bits=right(bits, pins, 0) /*right justify pin readings (values). */
say '───────── For a' pins "pin RS─232 plug, with a reading of: " ox
say
do j=1 for pins; z=substr(bits, j, 1); if z==0 then iterate
say right(j, 5) 'pin is "on": ' @.pins.j
end /*j*/
return

output   when using the default (internal) inputs:

───────── For a 24 pin RS─232 plug, with a reading of:  127

   18 pin is "on":  ??? unassigned pin
   19 pin is "on":  SRS secondary RTS
   20 pin is "on":  DTR data terminal ready
   21 pin is "on":  SQD signal quality detector
   22 pin is "on":  RI  ring indicator
   23 pin is "on":  DRS data rate select
   24 pin is "on":  XTC external clock

───────── For a 24 pin RS─232 plug, with a reading of:  020304x

    7 pin is "on":  SG  signal ground
   15 pin is "on":  TC  transmit clock
   16 pin is "on":  SRD secondary RD
   22 pin is "on":  RI  ring indicator

───────── For a 9 pin RS─232 plug, with a reading of:  10100000b

    2 pin is "on":  RD  received data
    4 pin is "on":  DTR data terminal ready

Ruby[edit]

Uses the BitStruct module, which is handy but awkward to instantiate objects.

require 'bit-struct'
 
class RS232_9 < BitStruct
unsigned :cd, 1, "Carrier detect" #1
unsigned :rd, 1, "Received data" #2
unsigned :td, 1, "Transmitted data" #3
unsigned :dtr, 1, "Data terminal ready" #4
unsigned :sg, 1, "Signal ground" #5
unsigned :dsr, 1, "Data set ready" #6
unsigned :rts, 1, "Request to send" #7
unsigned :cts, 1, "Clear to send" #8
unsigned :ri, 1, "Ring indicator" #9
 
def self.new_with_int(value)
data = {}
fields.each_with_index {|f, i| data[f.name] = value[i]}
new(data)
end
end
 
num = rand(2**9 - 1)
puts "num = #{num}"
 
sample1 = RS232_9.new([("%09d" % num.to_s(2)).reverse].pack("B*"))
puts sample1.inspect_detailed
 
sample2 = RS232_9.new_with_int(num)
puts sample2.inspect_detailed
 
puts "CD is #{sample2.cd == 1 ? 'on' : 'off'}"
num = 37
RS232_9:
                Carrier detect = 1
                 Received data = 0
              Transmitted data = 1
           Data terminal ready = 0
                 Signal ground = 0
                Data set ready = 1
               Request to send = 0
                 Clear to send = 0
                Ring indicator = 0
RS232_9:
                Carrier detect = 1
                 Received data = 0
              Transmitted data = 1
           Data terminal ready = 0
                 Signal ground = 0
                Data set ready = 1
               Request to send = 0
                 Clear to send = 0
                Ring indicator = 0
CD is on

Tcl[edit]

This Tcl implementation represents the fields as bits in an integer. It provides two functions to get from symbolic pin names to the integer, and vice versa.

set rs232_bits {CD RD TD DTR SG DSR RTS CTS RI}
 
proc rs232_encode args {
set res 0
foreach arg $args {
set pos [lsearch $::rs232_bits $arg]
if {$pos >=0} {set res [expr {$res | 1<<$pos}]}
}
return $res
}
proc rs232_decode int {
set res {}
set i -1
foreach bit $::rs232_bits {
incr i
if {$int & 1<<$i} {lappend res $bit}
}
return $res
}
#------------------------------ Test suite
foreach {test => expected} {
{rs232_encode CD} -> 1
{rs232_decode 1} -> CD
{rs232_encode CD RD TD} -> 7
{rs232_decode 7} -> {CD RD TD}
} {
catch $test res
if {$res ne $expected} {puts "$test -> $res, expected $expected"}
}