LeafLabs Garden » Topic: Serial Problem?

LeafLabs Garden » Topic: Serial Problem? http://forums.leaflabs.com/topic.php?id=249 A place to share, learn, and grow... en-US Fri, 22 Jan 2016 00:05:27 +0000 http://bbpress.org/?v=1.0.2 <![CDATA[Search]]> q http://forums.leaflabs.com/search.php x893 on "Serial Problem?" http://forums.leaflabs.com/topic.php?id=249#post-1864 Thu, 21 Oct 2010 02:48:05 +0000 x893 1864@http://forums.leaflabs.com/ You're right. I use while(SerialX.available()) { ... SerialX.read(); } not depends from negative or positive. Also easy to check. Send 60 bytes and read all. Send next 60 bytes (w/o read) and print SerialX.available() value gbulmer on "Serial Problem?" http://forums.leaflabs.com/topic.php?id=249#post-1861 Wed, 20 Oct 2010 18:51:22 +0000 gbulmer 1861@http://forums.leaflabs.com/ I think the code for calculating the number of characters in the buffer is <code>return ((rb->tail - rb->head) & (rb->size-1));</code> This should turn the negative value from <code>(rb->tail - rb->head)</code> into a positive one, modulo the buffer size (which is a power of 2). (I think this is correct. I checked with my Mac's calculator in programmer mode, and it looks about right ?-) gbulmer on "Serial Problem?" http://forums.leaflabs.com/topic.php?id=249#post-1860 Wed, 20 Oct 2010 18:37:29 +0000 gbulmer 1860@http://forums.leaflabs.com/ x893 - Okay, I agree with you. That is the code I see for the usart Serial. The usart code uses the code in libmaple/ring_buffer.h Would you please check my logic? That part of libmaple looks like it contains bug to me in the ring_buffer.h code. /libmaple/wirish/comm/HardwareSerial.cpp contains: <code>HardwareSerial Serial2(USART2, 2250000UL, GPIOA_BASE, 2, 3, TIMER2, 3);</code> and defines: <pre><code>uint32 HardwareSerial::available(void) { return usart_data_available(usart_num); }</code></pre> /libmaple/libmaple/usart.h contains: <pre><code>static inline uint32 usart_data_available(uint8 usart_num) { return rb_full_count(&usart_dev_table[usart_num].rb); }</code></pre> ring_buffer.h contains: <pre><code>static inline uint32 rb_full_count(ring_buffer *rb) { return rb->tail - rb->head; }</code></pre> and <pre><code>typedef struct ring_buffer { uint32 head; uint32 tail; uint8 size; uint8 *buf; } ring_buffer;</code></pre> The size of the buffer is constrained to be a power of 2: <pre><code>static inline void rb_init(ring_buffer *rb, uint8 size, uint8 *buf) { ASSERT(IS_POWER_OF_TWO(size)); rb->head = 0; rb->tail = 0; rb->size = size; rb->buf = buf; }</code></pre> Let's imagine the buffer is 64 bytes long, a power of 2. Characters are added, and removed until head = 17 (characters are added to the tail, and removed from the head) Some more charactera are added, filling the buffer, and tail is wrapped around to the start of the buffer, and becomes 0. rb_full_count(...) will return 17 Let's repeat the experiment with the buffer size 128, another power of 2. A similar sequence of events, but more characters are written before the wrap around. So head = 17, and tail = 0 rb_full_count(...) will still return 17 so even though the buffer is bigger, the number of characters is the same. Do the same thought-experiment where head gets to 3 short of the size of the buffer, and then tail wraps to 0. Even though there are fewer characters, the value from rb_full_count(...) is even bigger. Does that seem correct? I think this is a bug. It should return the number of characters in the buffer. x893 on "Serial Problem?" http://forums.leaflabs.com/topic.php?id=249#post-1855 Wed, 20 Oct 2010 09:11:02 +0000 x893 1855@http://forums.leaflabs.com/ I'm not sure but you can check indetail. I see uint32 available() { return (uint8)tail - (uint8)head; } if tail = 5 and head = 250. i can absolutly sure that data not available than return 0. gbulmer on "Serial Problem?" http://forums.leaflabs.com/topic.php?id=249#post-1853 Wed, 20 Oct 2010 07:10:21 +0000 gbulmer 1853@http://forums.leaflabs.com/ x893 - why does <code>SerialUSB.available()</code> return a negative number when their are bytes available? That isn't the definition of SerialUSB.available(), or AFAIK, how it works. <a>http://arduino.cc/en/Serial/Available</a> <a>http://leaflabs.com/docs/maple/usb/</a> crenn on "Serial Problem?" http://forums.leaflabs.com/topic.php?id=249#post-1852 Tue, 19 Oct 2010 20:28:30 +0000 crenn 1852@http://forums.leaflabs.com/ while(SerialUSB.available() > 0){ is still valid. SerialUSB.available() returns type uint32. However I can still see what you mean. x893 on "Serial Problem?" http://forums.leaflabs.com/topic.php?id=249#post-1850 Tue, 19 Oct 2010 19:27:43 +0000 x893 1850@http://forums.leaflabs.com/ You must use while(SerialUSB.available()){ not a while(SerialUSB.available() > 0){ because available() return positive or negative if chars available. The same for Serial2 crenn on "Serial Problem?" http://forums.leaflabs.com/topic.php?id=249#post-1849 Tue, 19 Oct 2010 18:12:50 +0000 crenn 1849@http://forums.leaflabs.com/ That's SerialUSB, all messages sent are less than 255 characters, I can do it a lot better, yes, but currently that's not the issue. I'm sending the messages using the Serial Console. If I sending "Testing..." I only expect to see "Testing..." come back with that code! gbulmer on "Serial Problem?" http://forums.leaflabs.com/topic.php?id=249#post-1847 Tue, 19 Oct 2010 17:38:40 +0000 gbulmer 1847@http://forums.leaflabs.com/ May I ask, what is printing the <blockquote>TesTesting Testing... </blockquote> is it SerialUSB or Serial2? What should it say? I don't understand why that output is an error. I think there are the possibility of errors in the while loops <pre><code>while(SerialUSB.available() > 0){ buffer[i] = SerialUSB.read(); i++; }</code></pre> and <pre><code>while(Serial2.available() > 0){ buffer[i] = Serial2.read(); i++; }</code></pre> If there are more than 255 characters available, it is possible that a while runs off the end of the array. I'm not confident that this is causing the error, but I don't understand the pieces of the system, so it may be. It'd be easy enough to check when <code>i>=BUFFER_SIZE</code>, and flush the buffer immediately. crenn on "Serial Problem?" http://forums.leaflabs.com/topic.php?id=249#post-1825 Sun, 17 Oct 2010 06:54:49 +0000 crenn 1825@http://forums.leaflabs.com/ While testing out a bluetooth module for the first time today, I noticed a slight problem. Here's the example output: <blockquote><code>TesTesting Testing...</code></blockquote> It happens sort of randomly and only when I'm using the in built Serial Console. Output length is always the same as the input length, but can be jumbled a little. Here's the code I'm currently using: <a href="http://www.crennsmind.com/Code/Maple/Communication/Bluetooth-Bee/Serial-Link.txt" rel="nofollow">http://www.crennsmind.com/Code/Maple/Communication/Bluetooth-Bee/Serial-Link.txt</a>