Documentation error in Disk API

[ghost]

I have found another error in the MikeOS documentation.

All disk functions use the carry flag to report a disk error, except os_get_file_list which returns a blank string. However, the MikeOS documentation fails to mention that os_create_file and os_remove_file use the carry flag to indicate an error.

I checked your implementation and found your 'load_file', 'create_file' and 'remove_file' functions do not handle the carry flag. Additionally, in 'get_file_size' you return zero as the file size if a disk error occurs, which may be misleading.

[I8087]

Thanks for bringing this to my attention! I'll go through each of those functions later tonight or tomorrow to figure out what needs to be done. Unfortunately, mlib.h shows that get_file_size and load_file already return a value, so I think it'd be more of the programmer's responsibility to take care of it, rather than the libraries. For example, the code below should be sufficient enough in most cases.

#include "mlib.h"

int main(int argc, char** argv) {
    char *file = "example.txt";
    if(!file_exists(file)) {
        size = get_file_size(file);
        if (size < 28671) {
            /* Load 4 KiB away from this program. */
            load_file(file, 28672); /* This should probably return a pointer. */
                                    /* Example:  int *p = load_file(file, 28672); */
        } else {
            print_string("The File is too large to load!\r\n");
        }
    } else {
        print_string("Error loading the file!\r\n");
    }
}

This should catch most problems caused by disk I/O.

[I8087]

Actually, it might be better to have a global variable IO_FLAGS and every time a hardware I/O is preformed, the value of IO_FLAGS is updated with the current system flags. That way, you can be certain there's was a success/failure.

[ghost]

You could also return multiple values from the function by having an extra parameter that is an int* type. That is how I have currently implemented it. However, that is entirely up to individual style.

If you want to know the memory location after the end of the program, the Smaller C linker has a macro 'stop_alldata', that should expand to the location in memory after the program. Like so:

extern unsigned int _stop_all_data__;
#define ramstart &_stop_all_data__
load_file(file, ramstart);

Hopefully the C compiler will not mangle the constant name.

I am a little concerned about the return value of MikeOS's os_get_file_size, in that it does not account for "slack space". I will raise this issue on the MikeOS forum, in the meantime you should round up to the nearest 512 bytes.

[I8087]

Thanks for all the info, I think the easiest way would be to implement a global variable kinda like C's errno, but like you said it's all up to individual style. Also, thanks for those two last tid bits. It's nice to know exactly where the program ends and silly me, I forget MikeOS loads the entire end sector, even if it's not completely used.

[I8087]

Alright, ioerr will be used. The list below will be used to help me keep track of its implementation.

• Disk API
• Serial API