CRC works fine for detecting random errors in data that might occur, for example, from network interference, line noise, distortion, etc. CRC is computationally much less complex than MD5 or SHA1. Using a hash function like MD5 is probably overkill for random error detection. However, using CRC for any kind of security check would be … Read more
Some USB hubs have the ability to turn power off to its downstream devices. “Is it possible to power up ports on a USB hub from Ubuntu?” https://askubuntu.com/questions/149242/is-it-possible-to-power-up-ports-on-a-usb-hub-from-ubuntu Which points to some c source for hub-ctrl.c See: http://www.gniibe.org/development/ac-power-control-by-USB-hub/index I tested this on Ubuntu with a Dream-Cheeky USB LED unit, and it did seem to turn … Read more
The following works for me. The parameter volume is to be given in the range [0, 100]. Beware, there is no error handling! void SetAlsaMasterVolume(long volume) { long min, max; snd_mixer_t *handle; snd_mixer_selem_id_t *sid; const char *card = “default”; const char *selem_name = “Master”; snd_mixer_open(&handle, 0); snd_mixer_attach(handle, card); snd_mixer_selem_register(handle, NULL, NULL); snd_mixer_load(handle); snd_mixer_selem_id_alloca(&sid); snd_mixer_selem_id_set_index(sid, 0); … Read more
Professional embedded systems are designed like this: Pick a MCU with power-on-reset interrupt and on-chip watchdog. This is standard on all modern MCUs. Implement the below steps from inside the reset interrupt vector. If the MCU memory is simple to setup, such as just setting the stack pointer, then do so the first thing you … Read more
GCC docs : -fstack-usage Makes the compiler output stack usage information for the program, on a per-function basis. The filename for the dump is made by appending .su to the auxname. auxname is generated from the name of the output file, if explicitly specified and it is not an executable, otherwise it is the basename … Read more
You can use the _alloca function. I believe that it’s not exactly Standard, but as far as I know, nearly all common compilers implement it. When you use it as a default argument, it allocates off the caller’s stack. // Header typedef struct {} something; int get_size(); something* create_something(void* mem); // Usage handle* ptr = … Read more
The most common way to determine the deepest stack usage is to initialize the stack memory with some known but unusual value, then periodically (or at the end of a big test run) see where that pattern stops. This is exactly how the IAR IDE determines the amount of stack used.
I would use HDLC. I have had good luck with it in the past. I would for a point to point serial just use the Asynchronous framing and forget about all of the other control stuff as it would probably be overkill. In addition to using HDLC for the framing of the packet. I format … Read more
Integer Square Roots by Jack W. Crenshaw could be useful as another reference. The C Snippets Archive also has an integer square root implementation. This one goes beyond just the integer result, and calculates extra fractional (fixed-point) bits of the answer. (Update: unfortunately, the C snippets archive is now defunct. The link points to the … Read more
An object marked as const volatile will not be permitted to be changed by the code (an error will be raised due to the const qualifier) – at least through that particular name/pointer. The volatile part of the qualifier means that the compiler cannot optimize or reorder access to the object. In an embedded system, … Read more