USBMSD check USB connected LPC1768

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1

Hi Everyone,
I hope you can help me with an issue in USB port. I am using LPC1768 with USB API USBMSD and I need to detect when USB is connected to PC in order to make a change of context in my program. I am using MBED Studio IDE with Mbed OS 6.6.0. I am trying to use USBMSD::connect() but I don’t know very well how use this method.

Thanks for your help.
Best Regards

2

Hello,

How I remember, first what you need is set USBMSD to non blocking mode in its constructor.

USBMSD usb(&sd, false);

And then somewhere (it is depend on application) periodically call the connect method until it is not true.

    while (true){ 
        if(usb.connect()){
            // your code for usb
        }
        thread_sleep_for(500);
    }

Also you can do it in a separate thread instead of the main and so on.

BR, Jan

3

Hi @JohnnyK thanks for your reply. I implemented your code but i had unexpected behavior. The program enters to “if” statement always, when i have or not the usb cable connected to pc. I have the next thread implemented.

SDBlockDevice sd(p5, p6, p7, p8);
FATFileSystem fs(“fs”);
USBMSD usb(&sd, false);

static DigitalOut led3(LED3);

void USB_thread()
{
while(true)
{
printf(“Thread USB.\r\n”);
if(usb.connect())
{
led3 = 1;
printf(“USB conectado.\r\n”);
}
thread_sleep_for(500);
}
}

I don’t know what I am doing wrong.

Best Regards

4

Ye, you are right, I was wrong and it’s nonsense. Sorry.

BR, Jan

5

Don’t worry. I think the best option is to check the VBUS pin on USB port.

Best Regards

6

I do not know if is something similar is possible with the LPC1768. But with Nucleo-F429ZI is possible to detect connected USB cable via PA_9 pin what is connected to VBUS .

So if it is not possible with the LPC, then you maybe can do it with 5V from USB cable as external interrupt or digital input. For safety by means of a transistor maybe.

For example with Interrupts - click here 
#include "mbed.h" // MbedOS 6.5 with Nucleo-F429ZI
#include "SDBlockDevice.h"
#include "USBMSD.h"

DigitalOut led1(LED1);
SDBlockDevice sd(PC_12, PC_11, PC_10, PC_9);
USBMSD usb(&sd, false);
InterruptIn usbVbus(PA_9);
volatile bool isConnected = DigitalIn(PA_9).read();

void riseVbus(){
    isConnected = true;
}

void fallVbus(){
    isConnected = false;
}

int main(){
    printf("Start\n");

    usbVbus.rise(&riseVbus);
    usbVbus.fall(&fallVbus);

    thread_sleep_for(500);
    bool conn = false;
    while(true){
        if(isConnected && !conn){
            printf("USB cable is connected!\n");
            conn = usb.connect();
        }
        if(!isConnected && conn){
            printf("USB cable is not connected!\n");
            conn = false;
            usb.disconnect();
        }
        if(conn){
            usb.process();
        } else{
            thread_sleep_for(500);
            led1 = !led1;
        }
    }
    return 0;
}
For example without Interrupts - click here 
#include "mbed.h" // MbedOS 6.5 with Nucleo-F429ZI
#include "SDBlockDevice.h"
#include "USBMSD.h"

DigitalOut led1(LED1);
SDBlockDevice sd(PC_12, PC_11, PC_10, PC_9);
USBMSD usb(&sd, false);
DigitalIn usbVbus(PA_9);

int main(){
    printf("Start\n");

    thread_sleep_for(500);
    bool conn = false;
    while(true){
        if(usbVbus.read() && !conn){
            printf("USB cable is connected!\n");
            conn = usb.connect();
        }
        if(!usbVbus.read() && conn){
            printf("USB cable is not connected!\n");
            conn = false;
            usb.disconnect();
        }
        if(conn){
            usb.process();
        } else{
            thread_sleep_for(500);
            led1 = !led1;
        }
    }
    return 0;
}

BR, Jan

7

Ah, we wrote post probably same time. I also wrote about the VBUS above.

BR, Jan

1 Like
8

I finally implemented pin p19 as DigitalIn and everything works well in order to detect when usb cable was connected (without interrupt). Thanks for your reply.

9

Wanted to implement the same on another target.
I think both of JohnnyK’s examples should be placed in the documentation of the USBMSD API.

1 Like