http://forums.leaflabs.com/topic.php?id=1179 A place to share, learn, and grow... en-US Fri, 22 Jan 2016 00:07:20 +0000 http://bbpress.org/?v=1.0.2 q http://forums.leaflabs.com/search.php http://forums.leaflabs.com/topic.php?id=1179#post-7225 Wed, 23 Nov 2011 20:32:28 +0000 gbulmer 7225@http://forums.leaflabs.com/ <p>fkatzenb - I agree with tdc218 and becker, just use one of the USARTs.</p> <p>Get yourself a copy of RM0008 from ST.com to see how very flexible the USARTs are.</p> <p>At such a slow data rate (less than one character/millisecond), it isn't likely the extra complexity of using DMA will save much work. Further the protocol you describe appears to be only a few bytes at a time in either direction before it needs processor involvement. So you might burn more cycles setting up the DMA for a short (e.g. 2 or 3 byte) transfer, as just dealing with the USART directly.</p> <p>Using an interrupt service routine to allow the program to do other work might be worth investigating if other processing is asynchronous and can't be done using DMA or interrupts. </p> http://forums.leaflabs.com/topic.php?id=1179#post-7218 Tue, 22 Nov 2011 14:51:25 +0000 becker 7218@http://forums.leaflabs.com/ <p>Further, the underlying hardware uses a "fractional baud rate generator". This increases the transmit accuracy over a simple integer division of the high speed clock by having a correction fraction.</p> <p>Not that it should matter for an async serial link, which resynchronizes with each start bit. </p> http://forums.leaflabs.com/topic.php?id=1179#post-7210 Mon, 21 Nov 2011 22:21:13 +0000 tdc218 7210@http://forums.leaflabs.com/ <p>As the "baud" rate divisor that gets programmed into the usarts is computed on the fly and not pulled from a look up table, you are not locked in to standard "baud" rates. You ought to be able to do Serial.begin(976); and/or Serial.begin(7812); and use the standard serial functions and it should have a good chance of working fine. </p> http://forums.leaflabs.com/topic.php?id=1179#post-7207 Mon, 21 Nov 2011 03:05:12 +0000 HDS 7207@http://forums.leaflabs.com/ <p>Nonblocking SoftSerial is throughoutly without problem on the Maple / Maple IDE:<br /> You only have to use one or two of the four built-in hardware timers.</p> <p>The timer is connected to an interrupt routine, which you do use for sending the bytes in the desired baud rate.<br /> The baud rate could be configured up to 36.000.000 ;-)</p> <p>here is an example for a SoftSerial.send(), with a non-blocking output ring buffer:</p> <p><a href="http://pastebin.com/pRajtwAj" rel="nofollow">http://pastebin.com/pRajtwAj</a></p> <p>The same way, you could connect an interrupt to some receive pin to start your data receiving timer to generate the baud rate and fill your recieve buffer - independantly from the main.loop.</p> <p>But: you could use also one of the 3 USART's. Ask them in the loop, if they've got a char for you, if so, store it in your buffer (fastest with DMA.)</p> <p>At both baud rates, you will have definitely very, very many Processor cycles to do other stuff - as long as you arn't waiting with Delay() or While(!Serial1.Available()) do wait... </p> http://forums.leaflabs.com/topic.php?id=1179#post-7205 Sun, 20 Nov 2011 19:14:41 +0000 fkatzenb 7205@http://forums.leaflabs.com/ <p>Its for an old Motorola ECU and those are the baud rates it uses. It is rather dumb.</p> <p>The protocal is rather simple.<br /> "You send code 0x12 at 976 baud until the ECU replies with 0x12. You then switch to 7812 baud and send 0x12 to confirm hi-speed logging, ECU replies with 0x12 if confirmed. You then send single byte memory addresses to retrieve data; ECU replies with data at the location sent."</p> <p>My goal is to make a black box recorder for particular parameters instead of using a laptop. Coupled with a selector knob and SD card, I could have several different profiles of which they each log a different combination of parameters. </p> <p>I have done several microcontroller projects, but I make bad assumptions. My concern is that I am going to waste a lot of clock cycles waiting to receive data. Is there some kind of hardware buffer I could use? My ultimate goal is to combine with this a display with some smoothing algorithms.</p> <p>Thanks,<br /> Frank </p> http://forums.leaflabs.com/topic.php?id=1179#post-7203 Sun, 20 Nov 2011 15:30:05 +0000 HDS 7203@http://forums.leaflabs.com/ <p>Think about Software Serial.<br /> Just using a pin.<br /> And a Hardware Timer controlling the baud rate.<br /> No, you are using really horrible Baud rates...:<br /> 976 BAUD<br /> 7812 BAUD<br /> Sounds like Frequencies to receive some RTTY on a demodulated SSB receiver.<br /> Since the Baud rates are very low:<br /> Definitely, the Maple will handle those. </p> http://forums.leaflabs.com/topic.php?id=1179#post-7199 Sat, 19 Nov 2011 22:00:28 +0000 fkatzenb 7199@http://forums.leaflabs.com/ <p>I am thinking about getting a Maple for black box recording to an SD card. I am looking at it because it has a lot of memory and head room as the serial data that I need, I have to first request and then wait to receive at horrible baud rates - 976 and 7812. Will the Maple be able to handle these?</p> <p>Thanks,<br /> Frank </p>