Establishing serial communication over UART instead of USB in MAX25405 EVKIT

I think I know where I made a mistake. When I compiled the framework code, I was getting an error in the compiler

Error: Non-void function does not return a value [-Werror,-Wreturn-type] in "cmd.cpp", Line: 283, Col: 1

I went to the cmd.cpp file and added a return 0; at the end.

After which the code compiled without any errors.

But this return 0; statement will always return a 0 on the execution on the function in cmd.cpp file. 

And this may be the reason why I'm not receiving anything over UART.

Thanks! I'm a beginner at mbed. I have only used 8051 in Keil uvision and Arduino till date. I haven't used any advanced MCUs so I have a very little idea on using mbed command line interface as suggested by the readme file.

rsjawale24 said:

I'm a beginner at mbed

Don't worry, I found the documentation on the MbedOS website to be very helpful and you should pick it up fairly quickly. Nevertheless, if you get stuck or if there's something you do not understand just ask and I'm happy to help.

 I have never had to use the command line before now, as I prefer to rely on Mbed Studio. This is the first time I've used CLI to handle a GCC compile for Mbed.

Thanks! I'll surely message you if I need any help. 

I compiled the firmware using the code provided by Maxim and using the same version of mbed os as misaz. 

It succeeded but with 24 warnings!! 

This is when UART is set to 0 (disabled) in the interface.h file.

I uploaded the binary for USB and it worked with the Maxim GUI. So now I have the original binary for USB interface. Let me know if you need it, I can email it over to you. 

Excellent. I sent you a private message with my email address. Thanks very much.

I was experimenting with the different options on the MAX32620FTHR board to print serial messages. I created some simple code to test behaviour using the latest MbedOS 6.16.

I made life easier and also used a wrapper library, which you would need to import into your project: os.mbed.com/.../

Here is the example code:

/* mbedOS 6.16
 * Board: MAX32620FTHR
 * Copyright (c) C Gerrish
 * SPDX-License-Identifier: Apache-2.0
 */

#include "mbed.h"
#include "BufferedSerial.h"
#include "SerialStream.h"
#include "USBSerial.h"

// Blinking rate in milliseconds
#define BLINKING_RATE       1000ms

#define UART_BAUD_RATE      115200

BufferedSerial fthrUART(P3_1,P3_0, UART_BAUD_RATE);
// This SerialStream is a wrapper for Stream.h to give you printf
SerialStream<BufferedSerial> RXTX(fthrUART);

// true here blocks until USB serial monitor opens
// in Arduino you would use while(!Serial) for same effect
USBSerial USB(true, 0x0b6a, 0x4360, 0x0001);

int main()
{
    // Initialise the digital pin LED1 as an output
    DigitalOut led(LED1);

    int cntr = 0;

    while (true) {
        led = !led;
        ThisThread::sleep_for(BLINKING_RATE);
        USB.printf("hello USB world %d\r\n", cntr);
        RXTX.printf("hello RXTX world %d\r\n", cntr);
        printf("hello DEBUG world %d\r\n", cntr);
        cntr++;
    }
}

The mbed_app.json file:

{
    "target_overrides": {
        "*": {
            "platform.stdio-baud-rate": 115200,
            "platform.stdio-buffered-serial": 1
        }
    }
}

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[Post EDIT]

Looking at the original MAX25x05 gesture library again to see how the serial part could be adapted to OS6.16 I would say that you could use...

the UnbufferedSerial API for when USE_UART_INTERFACE = 1 as this only provide putc etc.

I've just realised that the above statement is not correct.

In OS6.xx, it is not that simple to use putc anymore. In fact, I think the only way I could find is though the SerialStream wrapper. Not worth the effort, IMHO. If I had read the UnbufferedSerial API documentation more carefully then I would see that it only provides a write function. Sorry about that.

and you could use BufferedSerial API for when USE_UART_INTERFACE = 0 as this provide buffered writes etc.

Hope that helps.

Hi thanks for this. The only problem with this is that I will have to re-write the entire code for the gesture sensor. What I'm aiming for is just to get the gesture results over UART instead of the USB connection. As per the application note from Maxim, this should be possible. 

I'm trying to read the values from the MAX32620 board using Arduino. Here's my code. I'm not sure if this is correct.

int ges_res = 0;  //variable to store gesture result

void setup() {
  // put your setup code here, to run once:
Serial.begin(115200);         //initialise serial comm. at 115200 baud

}

void loop() {
  // put your main code here, to run repeatedly:
Serial.write("ver");         //send a command to the MAX32620FTHR firmware as it expects a command from user
delay(1000);                //delay to slow down the interval at the command is being sent to the FTHR board
ges_res = Serial.read();   //read the ges_res from MAX32620 board
Serial.println(ges_res);        //print the result on the serial monitor
}

I was thinking about how we could minimise changes in the code, so here is one option that simplifies things.

This code will either print to the debug/console UART pins (as defined in pinNames.h) or to UART pins of choice.

#include "mbed.h"

#define USE_UART_INTERFACE 1

#if USE_UART_INTERFACE
    #define printf(f_, ...) fprintf((f_), __VA_ARGS__);
#else
    #define printf(f_, ...) printf( __VA_ARGS__);
#endif

BufferedSerial otherUART(P3_1,P3_0,MBED_CONF_PLATFORM_STDIO_BAUD_RATE);
FILE* myTX = fdopen(&otherUART, "r+");

// main() runs in its own thread in the OS
int main()
{
    printf(myTX,"Hello New World\r\n");

    while (true) {

    }
}

Today I tried to read the UART from the MAX32620 into a FT232 USB to UART interface, it seems that the MAX32620 is not sending anything over UART. This is for the framework code provided by Maxim

Are you still using your version of MbedOS?

Just to say that I have managed to get the firmware working with the latest MbedOS 6.16 and have tested it using a Windows laptop with the Maxim GUI software. It all works. I'll post some guidance if you need it. Basically this is cleaner as you do not need to download the separate USBdevice or the MAX32620 libraries. All I had to do was amend a couple of lines in interface.cpp.

So, basically I ignored the UART option as there really is no point using this option when the shield is attached to the MAX32620FTHR board, because you cannot readily get access to the GPIO's unless putting it on a breadboard or soldering wires.

But, if I wanted to use UART in the latest MbedOS 6.16 I would then have to use with BufferedSerial or UnbufferedSerial API and then I would need to amend the code in CMD.cpp as, unlike USBSerial, these API's don't provide printf or getc functions.