I wrote a barebone progran template in XC8 (1.37) that I use to develop and test new GLCD functions for the 18F family. Programming is done via a PICkit3. Since I need to quicky reprogram several times the code it is really important that programming is faster as much as possible.
Tipically, the code size is around 2K and it takes less than 10 sec to program,
Everiything is fine until I must use a font table, defined as:
const char font8[] = {....
Now, with just $400 bytes added, the compiler place the table at the ROM's end and the programming of 64K memory takes more than 1 minute.
Is there any way to avoid this?
I tried to manually limit the memory range in the MPLABX options, but this is annoying and a little unsafe (sometimes part of code is truncated).
A while back I had to write some code for emissions testing, where I needed to copy data between extreme ends of RAM. To do that I needed to specify the exact memory addresses. You can also use the C extension __at() construct. http://ww1.microchip.com/downloads/en/DeviceDoc/50002053F.pdf#page=27
int scanMode __at(0x200);
const char keys[] __at(123) = { ’r’, ’s’, ’u’, ’d’};
int modify(int x) __at(0x1000) {
return x * 2 + 3;
}
Related
In an effort to better understand RSA I've been fooling around with the source code for GunPG 1.4, specifically the RSA implementation in the rsa.c file. As the title says, I can't figure out where the padding is happening.
So typically in RSA, padding is done right before the encryption and is taken off during the decryption. Encryption first starts around line 409 where we see
int
rsa_encrypt( int algo, MPI *resarr, MPI data, MPI *pkey )
{
RSA_public_key pk;
if( algo != 1 && algo != 2 )
return G10ERR_PUBKEY_ALGO;
pk.n = pkey[0];
pk.e = pkey[1];
resarr[0] = mpi_alloc( mpi_get_nlimbs( pk.n ) );
public( resarr[0], data, &pk );
return 0;
}
That seems easy, it's giving data to "public" function higher up on line 220. Public is responsible for calculating the important (c = m^e mod n) process. That all looks like:
static void
public(MPI output, MPI input, RSA_public_key *pkey )
{
if( output == input ) { /* powm doesn't like output and input the same */
MPI x = mpi_alloc( mpi_get_nlimbs(input)*2 );
mpi_powm( x, input, pkey->e, pkey->n );
mpi_set(output, x);
mpi_free(x);
}
else
mpi_powm( output, input, pkey->e, pkey->n );
}
Wait a second...now it looks like public is passing the job of that calculation off to mpi_powm() located in the mpi-pow.c file. I'll spare you the details but that function gets really long.
Somewhere in all of this some sort of PKCS#1 padding and unpadding (or something similar) is happening but I can't figure out where for the life of me. Can anyone help me see where the padding happens?
In an effort to better understand RSA I've been fooling around with the source code for GnuPG 1.4, specifically the RSA implementation in the rsa.c file.
Since you’re looking at the older (< 2.0) stuff anyway, and since it’s only for learning purposes, I would rather advise you to check out “ye olde rsaref.c from gnupg.org” where the padding is implemented in a pretty obvious way.
… some sort of PKCS#1…
To be exact, GnuPG uses PKCS #1 v1.5 (specified in RFC 4880).
Can anyone help me see where the padding happens?
Hmmm, let’s see if I can wrap that up somewhat logically. GnuGP pads according to PKCS #1 v1.5, so it just adds random pad to satisfy length requirements.
If you take a look at the cipher/pubkey.c file (which includes the rsa.h file in its head), you’ll notice a pubkey_table_s struct which defines a list of elements that define the key. For padding reasons, random bytes are appended to that list (better: after that struct). It’s done that way because those random bytes can easily be stripped by looking for the end of the list. Keeping a long story short, that’s where random.c probably starts to make a bit more sense to you. Now, all that stuff (and a whole lot more) is compiled into a lib called libcipher… which in itself is compiled to be used by functions that add the padding and handle the RSA stuff the way you expected it. In the end, the compiled executables use the functions libcipher provides to take care of the padding – depending on the individual need for padding.
So what you currently expect to find in 1 or 2, maybe 3 files is actually spread out across more than half a dozen files… which I regard not to be the best base for your learning efforts. As said, for reference purposes, I’ld go for the old rsaref.c they once started out with.
Not sure if this actually provides all the details you wanted to get, but it should give you a first good heads-up… hope it helps.
GPG 1.4 doesn't use any padding at all. It encrypts the raw session key.
Can anybody tell me how to measure the consumed RAM for a particular code running on Arduino Mega or Due.
There is two kinds of numbers to this question:
Global static usage and current run time.
The static estimated usage can be determined by adding the following line to (if it does not already exist)
.\arduino-1.5.5\hardware\arduino\avr\boards.txt
uno.upload.maximum_ram_size=2048
This then allows the compiler to output the additional 2nd line in the following example in the IDE's result window
Binary sketch size: 25,880 bytes (of a 32,256 byte maximum)
Estimated used SRAM memory: 990 bytes (of a 2048 byte maximum)
To see the amount of memory used at any given point. Including memory space currently in use, that exists while only in functions and members. This includes the HEAP and such. I use the following MemoryFree library at specific points in the code to reveal the high-water. The readme explains how to save unnecessarily/unintentionally used RAM by prints.
Note: That while the original Arduino IDE 1.0.5's boards.txt files does contain these ram_sizes, it does not actually use display usage. Where the original Arduino IDE 1.5.5 does, along with Arduino ERW 1.0.5 does (an non-supported fork).
In my Arduino IDE 2.1.0
I edit the file: /usr/share/arduino/hardware/arduino/boards.txt
but the second line don't appear
After read:
check-ram-memory-usage-arduino-optimization
measuring-free-memory
I tried:
Show vervose output during compilation
and use avr-size /tmp/build4042914391435450796.tmp/XXXXXXX.cpp.elf
then i get my memory used
Best Regards!
int freeRam () {
extern int __heap_start, *__brkval;
int v;
int fr = (int) &v - (__brkval == 0 ? (int) &__heap_start : (int) __brkval);
Serial.print("Free ram: ");
Serial.println(fr);
}
I have a bizarre one here with the serial output when trying to write some code for my Arduino Uno.
I have this proto-code:
MyClass myclass;
void setup()
{
Serial.Begin(9600);
Serial.println("Starting...");
}
void loop()
{
int status = myclass.DoWork();
Serial.println("Status: " + status);
}
class MyClass
{
int DoWork()
{
Serial.println("Doing some work...");
return 1;
}
}
Now when this runs I get the following output:
Starting...
Doing some work...
atus: 1
So the strange part is the "Status: 1" missing the first few characters. Is this because I am using serial in an object improperly or something?
I have noticed when I reference another library that also uses serial like MyClass does that I get other strange output behavior... so I assume that I am doing something wrong.
EDIT: In the end this turned out to actually be a memory issue. A library I was including was quite large and it was consuming the available memory. I found this by adding a few more debugging statements and found the corruption shifted around based on the string lengths and positions. By using the F() function I moved the strings to flash memory (e.g. I now run Serial.println(F("Starting...")); and it has corrected the strange output.
You cannot add strings and integers in C++. It would have been better for you if this failed to compile:
Serial.println("Status: " + status);
Instead the compiler guessed at something. It guessed wrong. Use this:
Serial.print("Status :");
Serial.println(status);
or for complete control of outputting numbers and strings learn to use C string formatting, sprintf()
In the end this turned out to actually be a memory issue. A library I was including was quite large and it was consuming the available memory. I found this by adding a few more debugging statements and found the corruption shifted around based on the string lengths and positions. By using the F() function I moved the strings to flash memory (e.g. I now run Serial.println(F("Starting...")); and it has corrected the strange output.
One more possible explanation.
I was running minicom to monitor, and I usually like that it auto-reconnects after resetting my device.
Well I minimized a terminal running minicom last night, and today I started a new instance that somehow also got connected to the same serial port (if that is even possible).
I think the two instances of minicom were each reading ~50% of the serial characters roughly at random, leaving me with quite a mess of text.
In standard Pascal (ISO7185), there was no procedure Assign that would've let a programmer to assign some kind of file name to a file variable. It only appeared in Turbo Pascal and other derivates.
So... how am I supposed to open a handle to a specific file if I comply with the standard?
Closest I've found is this Irie Pascal example:
program vowels(f, output);
var
f : file of char;
tot, vow : integer;
c : char;
begin
reset(f);
tot := 0;
vow := 0;
while not eof(f) do
begin
read(f, c);
case c of
'a', 'e', 'i', 'o', 'u',
'A', 'E', 'I', 'O', 'U'
: vow := vow + 1;
otherwise
end;
tot := tot + 1;
end;
writeln('Total characters read = ', tot);
writeln('Vowels read = ', vow)
end.
which suggests I might be able to give the file name as a startup parameter. This works using Irie Pascal. However, if I try to use that with P5, which should be closest to standard-compiliant Pascal compiler for modern computers I've found, I get (after replacing 'otherwise') **** Error: external file unknown 'f '. So, what'd be the standard way? Or is this actually the standard way and P5 is doing something wrong?
Edit: standard also gives a sample
program copy (f, g);
var f,g : file of real;
begin
reset(f) ; rewrite(g);
while not eof(f) do
begin
g^ := f^ ; get(f) ; put(g)
end
end.
but I haven't been able to get that to work with any compiler.
Edit2:
Doing it like this:
program copy (f, g);
var f,g : file of char;
begin
reset(f) ; rewrite(g);
while not eof(f) do
begin
g^ := f^ ; get(f) ; put(g)
end
end.
works just fine in Irie and is compliant with the standard. Using that, file name can be given as a startup parameter.
However, as explained by Marco van de Voort,
ISO 7185 does not have any standard way for a program to specify
file names at all, so any such way is already beyond 7185 (Bind
is ISO 10206, Assign is UCSD/BP, the 2nd parameter to Reset is
an extension of GPC and I think some other compilers).
(source)
IIRC this was for VMS support where the OS bound files before starting the program.
Unbound files were automatically tempfile iirc. Search the GNU Pascal maillists (old archives, say 2005 or so), they had quite some discussions about ISO file implementation.
It was Scope on the CDC 6000 series machines. However, the rest is correct. You basically assigned external files to logical header file names in the Scope command language.
Of course this seems very tedious now, but these were the days of the batch mode computer, where everything was submitted as a "deck" of cards to be run as input, then collected as a series of output "cards". Tape reels got rid of the actual cards, but tapes were treated as a collection of cards on a tape.
In normal use, Wirth's original compilers were actually limited to just an input and an output file. If you wanted more than one input file, you concatenated them. This was easier than it sounds, since most input and output files were text, and every file had distinct end tolkens in it.
This paradigm fit well with the idea that you mounted an input tape and an output tape for a job on a batch system. The job of the batch computer was to linearly process the input tape and produce the output tape. A large and fast machine would have several jobs concatenated onto a single tape and run sequentially.
The option of a high speed printer typically rounded out the system. Thus, a college kid in the 1960s learning computer science would punch a deck on what looked like a typewriter (or get it typed by a keypunch operator), then that deck would be collected and transcribed to a tape deck and scheduled to run. An hour or more later, you were handed a section of greenbar from the printer that represented the output from your program.
Anyways, its always a good debate question as to why Wirth put that limitation in the language. Probabaly it was for the simple reason that the CDC 6000 machines could not have dealt with a feature that randomly opened a file by name. Also remember that the predecessor to Pascal, Algol, had no I/O statements whatever! They considered I/O to be inherently machine specific.
Scott Moore
I have an old AIR file that works fine. I tried to recompile it but the resulting airfile is buggy.
After digging in the code, i found that at some place strings are parsed to ints, and that the resulting int does not correspond to the string.
So i made a simple Actionscript file and executed the code:
var test:int = parseInt("3710835714");
and the variable will have the value
-584131582
So this looks like an overflow. But i'm surprised that the air file i have (which i didn't compile myself) runs just fine. So I wonder - does the internal representation of int somehow depend on what version of the Flex or AIR sdk libraries one is using for compiling?
//edit: it seems it boils down to this test:
var obj:Object = new Object();
obj.val="3710835714";
var test1:Boolean = (obj.val==-584131582);
var test2:Boolean = (int(obj.val)==-584131582);
this evaluates for me to
test1=false;
test2=true;
however - the this old AIR file seems to evaluate both cases to true. How can that be?
It is happening due to Give number exceeds ActionsScript Int limit
The int data type is stored internally as a 32-bit integer and comprises the set of integers from -2,147,483,648 (-231) to 2,147,483,647 (231 - 1),
and number 3,710,835,714 exceeds it by 1563352067
but your parse result shows compiler is considering it as Uint, whose Max limit is 4,294,967,295 i.e
-584131581 = 3,710,835,714 - 4,294,967,295
You should use Uint or Number for big whole-numbers/integers
this blog may helps you
ActionScript 3 Number data type problem with long integer values
Hopes that works