Why does the read with lsusb fails? - c

Question

I need to read the response from a control unit of a motor. After the write of a command beginning with ?, the motor unit should respond with some text. I.e. on ?MSG it should report its status. But when I try to read the status the unit sends nothing and the request ends with a timeout.
The code is pretty straightforward and uses libusb. The program detaches all active drivers from the device, attaches itself to the device, transfers the command ?MSG and waits for response. After that it detaches and ends.
Why there is no response? Is there any error in code or is it an issue of the motor unit? I am sure that commands are sent and received by the unit as the motor moves, for example, on PSET1=4000
#include <assert.h>
#include <string.h>
#define VENDOR_ID 0x0483
#define PRODUCT_ID 0x5740
#define BULK_EP_IN 0x03
#define BULK_EP_OUT 0x81 // From computer to control unit
#define INTERFACE_IN 0
#define INTERFACE_OUT 1
#define BUF_SIZE 64
int main()
{
libusb_context *ctx;
libusb_device_handle *dev_handle;
int r = 0;
int actual, length, received;
char cmd[] = "?MSG\r\n";
char buffer[BUF_SIZE];
length = strlen(cmd);
r = libusb_init(&ctx);
assert(r == 0);
/* Set verbosity level to 3, as suggested in the documentation */
libusb_set_debug(ctx, 3);
/* Get device handle */
dev_handle = libusb_open_device_with_vid_pid(ctx, VENDOR_ID, PRODUCT_ID);
assert(dev_handle != NULL);
/* Find out if kernel driver is attached on IN iface */
if(libusb_kernel_driver_active(dev_handle, INTERFACE_IN) == 1) {
printf("Kernel Driver Active\n");
assert(libusb_detach_kernel_driver(dev_handle, INTERFACE_IN) == 0);
printf("Kernel Driver Detached!\n");
}
if(libusb_kernel_driver_active(dev_handle, INTERFACE_OUT) == 1) {
printf("Kernel Driver Active\n");
assert(libusb_detach_kernel_driver(dev_handle, INTERFACE_OUT) == 0);
printf("Kernel Driver Detached!\n");
}
/* Claim IN interface of device */
r = libusb_claim_interface(dev_handle, INTERFACE_IN);
assert(r >= 0);
/* claim OUT interface of device */
r = libusb_claim_interface(dev_handle, INTERFACE_OUT);
assert(r >= 0);
/* Transfer commands */
r = libusb_bulk_transfer(dev_handle, BULK_EP_IN, (unsigned char *)cmd, length, &actual, 0);
assert(r == 0 && actual > 0 && actual == length);
printf("Written %s\n",cmd);
/* Now read response */
if (cmd[0] == '?') {
char buffer[BUF_SIZE] = "";
int received = 0;
do {
int i;
r = libusb_bulk_transfer(dev_handle, BULK_EP_OUT, (unsigned char *)buffer, BUF_SIZE, &received, 1000);
if(r == LIBUSB_ERROR_TIMEOUT) {
printf("Timeout\n");
} else {
assert(r == 0);
}
for(i = 0; i<BUF_SIZE;i++)
printf("%c",buffer[i]);
} while (received != 0);
}
/* Release devices */
r = libusb_release_interface(dev_handle, INTERFACE_IN);
assert(r == 0);
r = libusb_release_interface(dev_handle, INTERFACE_OUT);
assert(r == 0);
/* Clean */
libusb_close(dev_handle);
libusb_exit(ctx);
}
Here is a description of the device with sudo lsusb --verbose in case it's important:
Bus 003 Device 003: ID 0483:5740 STMicroelectronics STM32F407
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 2.00
bDeviceClass 2 Communications
bDeviceSubClass 0
bDeviceProtocol 0
bMaxPacketSize0 64
idVendor 0x0483 STMicroelectronics
idProduct 0x5740 STM32F407
bcdDevice 1.00
iManufacturer 1 STMicroelectronics
iProduct 2 STR75x Virtual COM Port
iSerial 3 Demo 1.000
bNumConfigurations 1
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 67
bNumInterfaces 2
bConfigurationValue 1
iConfiguration 0
bmAttributes 0xc0
Self Powered
MaxPower 0mA
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 1
bInterfaceClass 2 Communications
bInterfaceSubClass 2 Abstract (modem)
bInterfaceProtocol 1 AT-commands (v.25ter)
iInterface 0
CDC Header:
bcdCDC 1.10
CDC Call Management:
bmCapabilities 0x00
bDataInterface 1
CDC ACM:
bmCapabilities 0x02
line coding and serial state
CDC Union:
bMasterInterface 0
bSlaveInterface 1
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x82 EP 2 IN
bmAttributes 3
Transfer Type Interrupt
Synch Type None
Usage Type Data
wMaxPacketSize 0x0008 1x 8 bytes
bInterval 255
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 1
bAlternateSetting 0
bNumEndpoints 2
bInterfaceClass 10 CDC Data
bInterfaceSubClass 0 Unused
bInterfaceProtocol 0
iInterface 0
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x03 EP 3 OUT
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 0
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 0
Device Status: 0x0001
Self Powered

Answer 1

You can communicate with the device by the RS-232 protocol, because it provides a virtual COM port which is a CDC ACM class. The kernel driver is cdc_acm.
iManufacturer 1 STMicroelectronics
iProduct 2 STR75x Virtual COM Port
bInterfaceClass 2 Communications
bInterfaceSubClass 2 Abstract (modem)
bInterfaceProtocol 1 AT-commands (v.25ter)
iInterface 0
CDC Header:
bcdCDC 1.10
CDC Call Management:
bmCapabilities 0x00
bDataInterface 1
CDC ACM:
bmCapabilities 0x02
line coding and serial state
CDC Union:
bMasterInterface 0
bSlaveInterface 1
So you can communicate with the device by sending RS-232 commands to /dev/ttyACMx (or /dev/ttyUSBx) (replace x with the number on your system)
To check this you can use a terminal program like PuTTY,... 5 Linux / Unix Commands For Connecting To The Serial Console. You have to figure out the correct COM port settings (baud rate, parity, start/stop bits, etc.)
There are several RS-232 libraries, see C: cross-platform RS-232 serial library?
Check the dmesg output after plugin in the device to see which driver is used.