I have a third party device that is UART programmable.
I need to create a USB - UART bridge with a functional password (programming only after entering the correct password)
generated the code using the latest version of STM32CubeMX for Atollic TrueSTUDIO for STM32 9.3.0 ...
I transfer data between USB and UART through a buffer (one for usb-uart, and another one for uart-usb)
when I try to transfer several characters everything is OK, but when I try to transfer a large data packet, problems start due to the fact that the USB speed is much higher than the UART ...
there are two questions:
1.How do I tell USB that I need to stop transferring data and wait until the UART (buffer) is busy
2.How on the side of the microcontroller to get the baud rate set on the PC (set when the terminal is connected to the virtual COM port)
USB provides flow control. That's what you need to implement. A general introduction can be found here:
https://medium.com/#manuel.bl/usb-for-microcontrollers-part-4-handling-large-amounts-of-data-f577565c4c7d
Basically, the setup for the USB-to-UART direction should be:
Indicate that the code is ready to receive a USB packet
Receive a USB packet
Indicate that you are no longer ready to receive a USB packet
Transmit the data via UART
Start over
Step 0: Initial setup
Call USBD_CDC_SetRxBuffer to set the buffer for receiving the USB data. Unless you use several buffers to achieve higher throughput, a single call at the start of the program is sufficient.
Step 1: Ready to receive data
Call USBD_CDC_ReceivePacket. Other than what the name implies, this function indicates that the app is ready to receive data. It immediately returns before the data has actually been received.
Step 2: Receive a USB packet
You don't need to do anything here. It will happen automatically. Once it's complete, CDC_Itf_Receive will be called.
Step 3: Indicate that you are no longer ready to receive a USB packet
Nothing to do here. This happens automatically whenever a packet has been received (and double buffering is not enabled).
Step 4: Transmit the data via UART
I guess you know how to do this. It's up to you whether you want to do it in a blocking fashion or using DMA.
Since a callback is involved, you cannot put this code into the main loop. It might be possible to put all code into CDC_Itf_Receive if blocking UART is used. It would appear in the order 2, 3, 4, 1. Additionally, initialization is needed (0 and 1).
In the UART-to-USB direction, you would need to implement flow control on the UART. The USB flow control is managed by the host. Even though USB is much faster than UART, flow control is relevant as the application on the host can process data as slow as it likes to.
Regarding question 2: I'm not sure I understand it... The microcontroller cannot set the baud rate on the host. Either the host can specify a baud rate (transmitted over USB and applied to UART), or if the UART has a fixed baud rate, you can ignore baud rate (any baud rate set on the host side will work as it does not apply to USB).
Related
In our application we are sending ADC data(240 bytes) to host computer through USB at full speed and using Serial application like (teraterm/minicom/Docklet) to validate the data, but we are facing the issue of data loss.
We are not getting where the issue is weather the seral application is not able to handle the incoming data or is there any limitations at controller side operating at USB full speed?
Microcontroller - NRF52840
USB class - CDC ACM
Best regards
Sagar
Suggest you entirely disable (temporarily) the ADC function and only have the microcontroller send a counting sequence to verify the known pattern is transferred without loss to the PC side. If the pattern is detected without loss, then re-enable the ADC function, but still only send the counting sequence and test again. If data is missing, then the problem is most likely the ADC function is causing a timing condition (such as blocking the CPU too long).
I have a relay contact closure event that needs to be timestamped accurately ( 1 msec) with a GPS and the PPS output... I am not sure how to feed the relay contact output to a microcontroller and then synchronize the microcontroller clock to the GPS ...plus how to get the UTC afterall?
Can you please help me.
thanks
If your microcontroller has at least two interrupts based on hardware pins, you could connect the relay to one of the interrupt-generating pins, and the PPS to the other interrupt-generating pin.
You will need to connect the NMEA (or other proprietary protocol of your GPS) to the corresponding port in your microcontroller. Some common buses are UART or SIP.
Then, every time that you get a PPS interrupt, you enable a global flag that can be used in the main loop to reset a counter. This counter will tell you how far apart from the PPS the relay switched (if it happens within that second). If you know the base frequency of your counter, you can convert the counter into fractions of seconds. Note that if both edges of the relay state change have to be detected, you will need an interrupt source capable to interrupt on both edges (or use two interrupts)
Then, if the Relay interrupt goes off, you can get the value of the counter upon interrupt, and save it in storage, send it to host, etc. (Note, it would be best to save the value in RAM, lift a flag of "value present", and leave the sending/storing to the main loop, then turning off the flag).
Finally, when you receive a complete NMEA message (this could be being parsed in your main loop by a state machine for instance), you can send this information to the host or storage along with the counter that you saved to time your relay state change. Note please that the NMEA message will be generated and decoded with a certain delay from the PPS, so you will need to compensate for that.
I'm in trouble with programming my Arduino. I've two XBee Series 2 Modules and an Arduino UNO. I use the XBee-API library from: http://code.google.com/p/xbee-api/.
I generate three RemoteATRequest Packets (0x17) to control a Digital Pin of the Remote Sleepy Node and send it out of a SoftwareSerial to the XBee Coordinator which is plugged via a Sparkfun XBee Arduino Shield (https://www.sparkfun.com/products/10854) to the Arduino UNO. The Communication works fine. Every Request Packet is sending out to the Remote. And for every Request Packet a Remote Packet is received. I checked this with a Serial Monitor and a RS232<-> TTL Converter. But in my Arduino Software it seems to be that only one Remote Packet is received. Curious is the point that when I send the Request Packets in the time the Remote is sleeping than I read three Response if it is awake and takes the Requests from the Coordinator.
Does anyone try the same or hase the same problems? I've tried so much until know another Baudrate, delays befor sending out. Nothing works.
My recollection of ZigBee and/or 802.15.4 is that the parent node for a sleepy end device will only hold/queue a single frame for when the sleepy device wakes up. And note that in ZigBee it's only guaranteed to queue it for 7.5 seconds. You may need to modify your code to send a single Remote AT Request at a time, and wait for the response before sending another.
This page has a good description about how the MAC layer works:
Once the frame is assembled, there are actually two ways to send it.
If its going to another router or an end device whose receiver is
always on, the frame will be sent directly via the radio. Otherwise,
if the destination is a sleepy end device, the frame will need to be
sent as an indirect transfer. The frame will go to the indirect queue
until the destination device wakes up and polls the parent. Once the
poll comes in, the frame will get sent to the destination.
It would be great if the XBee module supported a frame type that contains multiple AT commands, but as far as I can tell, that isn't an option.
I am working on an embedded project which includes two half duplex UARTS, and one full duplex UART.
UART1 is connected to Device A. UART2 is connected to Device B, and UART3 is connected to the PC. UART1 and UART2 are half-duplex, thus RX/TX modes have to be configured properly.
When a signal on UART1 is triggered, UART2 fetches some data from Device B. That data is put into a buffer, and then transmitted back to UART1, AND UART3. Device A consumes the data, and sends more items on UART1, which then has to be passed to UART2 for Device B to respond.
I was thinking about an efficient state machine that can handle the switching modes between TX/RX mode, and so far my UART code is interrupt driven. What would be some ways to tackle the flow of this program?
I don't think you will need a state machine for this case. Why not just hook up all interrupts accordingly and just forward anything received from one devivce to the other(s)?
You may want to include a TX (ring-)buffer to accomodate for different speeds of each UART and then just have a RX-ISR write the data received to the appropriate TX buffer(s), from where it will then be consumed by the other UARTs' UDRE-ISRs.
I have to send file byte-by-byte to serially connected AT89s52 from computer (VB.NET).
Every sended byte have some job to do in microcontroller what require some time.
Here is relevant part of my C code to receiving bytes:
SCON = 0x50;
TMOD = 0x20; // timer 1, mode 2, 8-bit reload
TH1 = 0xFD; // reload value for 9600 baud
TR1 = 1;
TI = 1;
again:
while(RI!=0)
{
P1=SBUF; // show data on led's
RI=0;
receivedBytes++;
}
if (key1==0)
{
goto exitreceive; // break receiving
}
show_lcd_received_bytes(receivedBytes);
// here is one more loop
// with different duration for every byte
goto again;
And here is VB.NET code for sending bytes:
For a As Integer = 1 To 10
For t As Integer = 0 To 255
SerialPort1.Write(Chr(t))
Next t
Next a
Problem is that mC have some job to do after every received byte and VB.NET don't know for that and send bytes too fast so in mC finishes just a part of all bytes (about 10%).
I can incorporate "Sleep(20)" in VB loop ant then thing will work but I have many of wasted time because every byte need different time to process and that would be unacceptable slow communication.
Now, my question is if 8051 can set some busy status on UART which VB can read before sending to decide to send byte or not.
Or how otherwise to setup such communication as described?
I also try to receive bytes with serial interrupt on mC side with same results.
Hardware is surely OK because I can send data to computer well (as expected).
Your problem is architectural. Don't try to do processing on the received data in the interrupt that handles byte Rx. Have your byte Rx interrupt only copy the received byte to a separate Rx data buffer, and have a background task that does the actual processing of the incoming data without blocking the Rx interrupt handler. If you can't keep up due to overall throughput issue, then RTS/CTS flow control is the appropriate mechanism. For example, when your Rx buffer gets 90% full, deassert the flow control signal to pause the transmit side.
As #TJD mentions hardware flow control can be used to stop the PC from sending characters while the microcomputer is processing received bytes. In the past I have implemented hardware flow by using an available port line as an output. The output needs to be connected to an TTL to RS-232 driver(if you are currently using a RS-232 you may have and extra driver available). If you are using a USB virtual serial port or RS-422/485 you will need to implement software flow control. Typically a control-S is sent to tell the PC to stop sending and a control-Q to continue. In order to take full advantage of flow control you most likely will need to also implement a fully interrupt driven FIFO to receive/send characters.
If you would like additional information concerning hardware flow control, check out http://electronics.stackexchange.com.
Blast from the past, I remember using break out boxes to serial line tracers debugging this kind of stuff.
With serial communication, if you have all the pins/wires utililzed then there is flow control via the RTS (Ready To Send) and DTR (Data Terminal Ready) that are used to signal when it is OK to send more data. Do you have control over that in the device you are coding via C? IN VB.NET, there are events used to receive these signals, or they can be queried using properties on the SerialPort object.
A lot of these answers are suggesting hardware flow control, but you also have the option of enhancing your transmission to be more robust by using software flow control. Currently, your communication is strong, but if you start running a higher baud rate or a longer distance or even just have a noisy connection, characters could be received that are incorrect, or characters could be dropped.
You could add a simple two-byte ACK sequence upon completion of whatever action is set to happen. It could look something like this:
Host sends command byte: <0x00>
Device echoes command byte: <0x00>
Device executes whatever action is needed
Device sends ACK/NAK byte (based on result):
This would allow you to see on the host side if communication is breaking down. The echoed character may mismatch what was sent which would alert you to an issue. Additionally, if a character is not received by the host within some timeout, the host can try retransmitting. Finally, the ACK/NAK gives you the option of returning a status, but most importantly it will let the host know that you've completed the operation and that it can send another command.
This can be extended to include a checksum to give the device a way to verify that the command received was valid (A simple logical inverse sent alongside the command byte would be sufficient).
The advantage to this solution is that it does not require extra lines or UART support on either end for hardware flow control.