Data logging via rs-232

mindstorm88 · Joined: 06 Dec 2006 Posts: 102 Location: Montreal , Canada

Hi guys, I need to log 4 (int16) every 500ms, is printf fast enough ?? Will it slow down all other process ?? Should I use putc instead ??

Thanks

jbmiller · Joined: 07 Oct 2006 Posts: 73 Location: Greensville,Ontario

Sure it can however..

Your data could be sent as 8 bytes.
Time depends on serial interface speed (110 baud ...115200 baud...?)
also how you 'create' your data (from rom,eeprom,a2d,calculations).

I suggest you doing this one step at a time,once you get it working, look over the listing and see where you can shave off time(if required), either by tighter C code or using assembler.

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

16 bytes per second is pretty slow. The overhead of printf() should not be a problem.
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mindstorm88 · Joined: 06 Dec 2006 Posts: 102 Location: Montreal , Canada

Douglas Kennedy · Joined: 07 Sep 2003 Posts: 755 Location: Florida

You don't need it but supposing printf was too slow at moments but on average OK. Say you have a few hundred lines of code then a long printf.
#INT TBA can be used with a transmit circular buffer. CCS has the printf to a function that is not hostage to the baud rate. The function drops the char into the buffer and the transmit isr chews on them sending them out while your main program slogs through your several hundred lines of code. A silly example. The baud rate is 110 and your printf is 100 chars.. 10 secs to execute the printf statement is not so good. The printf to a function does the printf at PIC speed to the buffer. Now over the next ten sec the isr chews away at the buffer but allows your main code to get on with things.