AN_347 FT51A Test and Measurement Sample

Application Note
AN_347
FT51A Test and Measurement
Sample
Version 1.1
Issue Date: 2015-11-26
This document provides a guide for using the FT51A development
environment to read sensors and send results to a host PC via the USB Test
and Measurement Class.
Use of FTDI devices in life support and/or safety applications is entirely at the user’s risk, and the
user agrees to defend, indemnify and hold FTDI harmless from any and all damages, claims, su its
or expense resulting from such use.
Future Technology Devices International Limited (FTDI)
Unit 1, 2 Seaward Place, Glasgow G41 1HH, United Kingdom
Tel.: +44 (0) 141 429 2777 Fax: + 44 (0) 141 429 2758
Web Site: http://ftdichip.com
Copyright © 2015 Future Technology Devices International Limited
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Table of Contents
1 Introduction ............................................................ 4
1.1 Overview.......................................................................... 4
1.2 Features........................................................................... 4
1.3 Limitations ....................................................................... 4
1.4 Scope ............................................................................... 4
2 Test and Measurement Overview.............................. 5
2.1 Firmware Overview .......................................................... 5
2.1.1
FT51A Libraries ...................................................................................................... 5
2.2 Labview Application Overview ........................................... 5
3 Test and Measurement Firmware ............................. 7
3.1 USB Descriptors................................................................ 7
3.1.1
TMC Descriptors ..................................................................................................... 8
3.1.2
DFU Descriptors ..................................................................................................... 9
3.1.3
Descriptor Selection ............................................................................................. 11
3.2 USB Class Requests ........................................................ 12
3.3 USB Reset Handler.......................................................... 14
3.4 Timer ............................................................................. 14
3.5 TMC Messages ................................................................ 15
3.6 Sensor Reading Acquisition ............................................. 16
3.6.1
Force Sensor ........................................................................................................ 16
3.6.1
Heart Rate Sensor................................................................................................ 17
3.6.2
Temperature Sensor............................................................................................. 18
4 LabView Application .............................................. 19
4.1 Requirements ................................................................. 19
5 Possible Improvements ......................................... 20
6 Contact Information .............................................. 21
Appendix A – References ........................................... 22
Document References ............................................................ 22
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Acronyms and Abbreviations .................................................. 22
Appendix B – List of Tables & Figures ......................... 23
List of Figures ........................................................................ 23
Appendix C – Revision History .................................... 24
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1 Introduction
This application note documents an example firmware project for the FT51A. The source code is
available in the “examples\AN_347_Test_and_Measurement_Sample” folder of the FT51A Software
Development Kit.
1.1 Overview
The Test and Measurement firmware and LabView application demonstrate a method for providing
data to LabView from an FT51A device. The FT51A need only be connected to a host PC via the
USB interface. The firmware responds to test and measurement class (TMC) requests and
message protocol to send readings from sensors to LabView. An application written in LabView on
the host PC will generate the TMC messages and process the responses. The readings from
sensors are displayed on the host PC.
The TMC class firmware will decode and respond to a subset of SCPI commands which are
delivered over USB by the TMC class.
The example code also include s the DFU functionality from AN_344 FT51A DFU Sample.
1.2 Features
The test and measurement example has the following features:
-
Open source firmware layered on the FT51A USB Library.
Implements a bulk IN and a bulk OUT endpoint pair.
Reads data from a temperature sensor using the SPI Master interface.
Converts the analogue voltage from a force sensor to a digital reading.
Detects transitions on an analogue voltage input to make a simple heart rate monitor.
The built-in USB hub on the FT51A is enabled in this example to allow up-to 4 FT51A EVM modules
to be chained together.
1.3 Limitations
The firmware does not implement a wide range of SCPI commands.
The firmware is designed for the FT51A EVM module. It can utilise the LCD for user feedback with
communications on the I2C Master bus. This is disabled by default as program space is limited –
the code to support it is conditionally compiled. (See section 3)
The size of the firmware code to support the TMC class and DFU class leaves very little space in
the program data area for expansion.
1.4 Scope
The guide is intended for developers who are creating applications, extending FTDI provided
applications or implementing example applications for the FT51A.
In the reference of the FT51A, an “application” refers to firmware that runs on the FT51A;
“libraries” are source code provided by FTDI to help user, access specific hardware features of the
chip.
The FT51A Tools are currently only available for Microsoft Windows platform and are tested on
Windows 7 and Windows 8.1.
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2 Test and Measurement Overview
The protocol and requirements for test and measurement devices are documented in the TMC
specification:
http://www.usb.org/developers/docs/devcla ss_docs/USBTMC_1_006a.zip
The FT51A implementation is for a USB device which decodes and responds to a small number of
SCPI commands.
Configuration descriptors for TMC devices have an interface descriptor containing a bulk IN and a
bulk OUT endpoint. They have a USB “Application” class and a subclass identifying the device as
Test and Measurement. The USB protocol indicates whether the device is a USB-488 interface or
not. This firmware does not provide a USB-488 interface.
2.1 Firmware Overview
The firmware will enumerate as a TMC device to the host. This will allow LabView to access the
device using SCPI commands sent over the TMC protocol.
The SCPI commands supported are “*IDN?” for IDeNtify, “*MEAS:hrm?” to return heart rate
MEASurement, “*MEAS:for?” for force sensor and “*MEAS:tmp?” for temperature sensor.
This does not cover the minimum set of SCPI commands that must be supported. However, the
LabView application does not require additional commands and a trade -off between spaces
available in the firmware and demonstrating multiple sensors has been made.
By default the FT51A Hub function is enabled in this firmware.
2.1.1
FT51A Libraries
The TMC firmware uses the FT51A USB library, DFU library, SPI Master library, TMC library,
general config library and the IOMUX library. The IOMUX library is not used in the example code
but is included to allow further functionality to be added. A code module for the ADT7310
temperature sensor (via the SPI Master library) is included.
The firmware is designed for the FT51A EVM module and may be extended to use the LCD for
displaying some information. If so, then it will need the I2C Master library added.
DFU functionality is implemented as described in AN_344 DFU Sample.
2.2 Labview Application Overview
A standalone LabView application and LabView source code is included with the firmware .
The user must also install the following software available from National Instruments website ,
which provides a good search facility:

LabVIEW Run-Time Engine (2013 version or compatible).
Note that different OS versions are available .
Running the TMC application when not installed gives the following error. Click yes to be
directed to the website for executable file download:
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Figure 2.2-1 LabVIEW Run-Time Engine Alert Dialog Box

NI Device drivers (2014.08 Part 1 and Part 2 at time of writing)
The application will repeatedly read the sensors from up to four connected FT51A EVM boards and
display this on a chart. The application uses the LabView VISA drivers.
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3 Test and Measurement Firmware
The firmware included in the example code demonstrates a test and measurement device.
The firmware is designed for the FT51A EVM module. It will use the force sensor, temperature
sensor and heart rate sensor. The force and heart rate sensors use an analogue voltage input
which is converted using the ADC features. The temperature sensor uses a n ADT7310 which is
connected to the FT51A via an SPI bus.
The DFU functionality is optional. It is normally enabled but can be disabled by setting the macro
DFU to zero in the header file tmc_app_usb.h and removing the DFU library. The LCD output can
also be enabled here by setting the LCD macro non-zero and adding both the LCD and I2C Master
libraries to the project.
Three additional macros in the same file enable or disable the code to read the sensors. These can
be changed individually to leave out the force, heart rate and temperature sensor reading code;
the macros are MEAS_FORCE, MEAS_HR and MEAS_TMP respectively.
However as program space is limited not all functions can be enabled at the same time.
Removing the DFU code will reduce the size of the compiled code by approximately 1600 bytes.
The LCD library code (I2C Master and LCD) total about 650 bytes.
In the project settings a symbol FT51A_INTERRUPTS is defined to remove support for unused
interrupts in the FT51A_interrupts.c file. Removing unused interrupt handers will reduce the size of
the compiled code.
When compiling, the SDCC command line will have the following macro added.
-D"FT51A_INTERRUPTS=(FT51A_INT_TIMER0+FT51A_INT_ADC+FT51A_INT_I2CM+FT51A_INT_PERIPHERALS)"
In Eclipse the symbol is defined in the Project Properties in the “Paths and Symbols” area of the
“C/C++ General” section. Compiler symbols are d efined in the “Symbols” Tab when “SDCC”
language is selected.
The FT51A_INT_I2CM macro is for the I2C Master and is included in case the LCD function is added.
FT51A_INT_PERIPHERALS includes the USB function.
In the USB library, there is a macro in the file FT51A_usb_internal.h called USB_MAX_ENDPOINT_COUNT
which can enable or disable code to support multiple endpoints on a device. The default value is
up-to 2 endpoints. This project has 2 non-control endpoints so the default value is left. If another
endpoint is added then the macro can be added to the “Paths and Symbols”.
3.1 USB Descriptors
The TMC firmware stores two sets of device descriptors and configuration descriptors. It stores a
single table of string descriptors as the strings for run time and DFU modes can be selected by the
descriptors as needed from the same table.
The control endpoint max packet size is defined as 16 bytes. The bulk IN and OUT endpoints for
sending the TMC messages are set to a maximum of 64 bytes. Internal to the firmware the siz e of
the buffer used for TMC messages is 64 bytes.
// USB Endpoint Zero packet size (both must match)
#define USB_CONTROL_EP_MAX_PACKET_SIZE 16
#define USB_CONTROL_EP_SIZE USB_EP_SIZE_16
// USB Bulk Endpoint packet size (both must match)
#define USB_BULK_EP_MAX_PACKET_SIZE 64
#define USB_BULK_EP_SIZE USB_EP_SIZE_64
// FTDI predefined TMC Demo Product ID.
#define USB_PID_DEMO 0x0feb
The Product IDs (PIDs) for run time (0x0FEB) and DFU mode (0x0FEE – the same as the AN_344
DFU Sample interface) are also defined in the source code.
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These are example PID values and must not be used in a final product. VID and PID combinations
must be unique to an application.
The USB class, subclass and protocols along with other general USB definitions are found in the file
FT51A_usb.h library include file.
3.1.1
TMC Descriptors
The first set of descriptors is the run time set for the TMC function. The device descriptor contains
the VID and PID for the TMC function.
__code USB_device_descriptor device_descriptor_demo =
{
.bLength = 0x12,
.bDescriptorType = USB_DESCRIPTOR_TYPE_DEVICE,
.bcdUSB = USB_BCD_VERSION_2_0,
// V2.0
.bDeviceClass = USB_CLASS_DEVICE,
// Defined in interface
.bDeviceSubClass = USB_SUBCLASS_DEVICE, // Defined in interface
.bDeviceProtocol = USB_PROTOCOL_DEVICE, // Defined in interface
.bMaxPacketSize0 = USB_CONTROL_EP_MAX_PACKET_SIZE,
.idVendor = USB_VID_FTDI,
// idVendor: 0x0403 (FTDI)
.idProduct = USB_PID_DEMO, // idProduct: 0x0feb
.bcdDevice = 0x0101,
// 1.1
.iManufacturer = 0x01,
// Manufacturer
.iProduct = 0x02,
// Product
.iSerialNumber = 0x03,
// Serial Number
.bNumConfigurations = 0x01
};
The configuration descriptor contains an interface descriptor, and 2 endpoint descriptors for the
run time function.
If the DFU macro is non-zero, it also has an interface descriptor for a DFU interface. This includes a
DFU functional descriptor. It must load the libusb-win32 driver for the DFU function to work.
// Structure containing layout of configuration descriptor
__code struct config_descriptor_demo
{
USB_configuration_descriptor configuration;
USB_interface_descriptor interface;
USB_endpoint_descriptor endpoint_in;
USB_endpoint_descriptor endpoint_out;
#if DFU
USB_interface_descriptor dfu_interface;
USB_dfu_functional_descriptor dfu_functional;
#endif // DFU
};
struct config_descriptor_demo config_descriptor_demo =
{
.configuration.bLength = 0x09,
.configuration.bDescriptorType = USB_DESCRIPTOR_TYPE_CONFIGURATION,
.configuration.wTotalLength = sizeof(struct config_descriptor_demo),
#if DFU
.configuration.bNumInterfaces = 0x02,
#else // DFU
.configuration.bNumInterfaces = 0x01,
#endif // DFU
.configuration.bConfigurationValue = 0x01,
.configuration.iConfiguration = 0x00,
.configuration.bmAttributes = USB_CONFIG_BMATTRIBUTES_VALUE,
.configuration.bMaxPower = 0xFA,
// 500mA
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// ---- INTERFACE DESCRIPTOR for Demo ---.interface.bLength = 0x09,
.interface.bDescriptorType = USB_DESCRIPTOR_TYPE_INTERFACE,
.interface.bInterfaceNumber = 0,
.interface.bAlternateSetting = 0x00,
.interface.bNumEndpoints = 0x02,
.interface.bInterfaceClass = USB_CLASS_APPLICATION, // Application class
.interface.bInterfaceSubClass = 0x03,
// Test and Measurement
.interface.bInterfaceProtocol = 0x00,
// 0x00 = USBTMC
// 0x01 = USBTMC USB488 interface.
.interface.iInterface = 0x06,
// "FT51A Demo"
// ---- ENDPOINT DESCRIPTOR for Demo ---.endpoint_in.bLength = 0x07,
.endpoint_in.bDescriptorType = USB_DESCRIPTOR_TYPE_ENDPOINT,
.endpoint_in.bEndpointAddress = 0x01,
.endpoint_in.bmAttributes = USB_ENDPOINT_DESCRIPTOR_ATT R_BULK,
.endpoint_in.wMaxPacketSize = USB_BULK_EP_MAX_PACKET_SIZE,
.endpoint_in.bInterval = 0x0,
// ---- ENDPOINT DESCRIPTOR for Demo ---.endpoint_out.bLength = 0x07,
.endpoint_out.bDescriptorType = USB_DESCRIPTOR_TYPE_ENDPOINT,
.endpoint_out.bEndpointAddress = 0x81,
.endpoint_out.bmAttributes = USB_ENDPOINT_DESCRIPTOR_ATTR_BULK,
.endpoint_out.wMaxPacketSize = USB_BULK_EP_MAX_PACKET_SIZE,
.endpoint_out.bInterval = 0x0,
#if DFU
// ---- INTERFACE DESCRIPTOR for DFU Interface ---.dfu_interface.bLength = 0x09,
.dfu_interface.bDescriptorType = USB_DESCRIPTOR_TYPE_INTERFACE,
.dfu_interface.bInterfaceNumber = DFU_USB_INTERFACE_RUNTIME,
.dfu_interface.bAlternateSetting = 0x00,
.dfu_interface.bNumEndpoints = 0x00,
.dfu_interface.bInterfaceClass = USB_CLASS_APPLICATION, // Application Specific Class
.dfu_interface.bInterfaceSubClass = USB_SUBCLASS_DFU, // Device Firmware Update
.dfu_interface.bInterfaceProtocol = USB_PROTOCOL_DFU_RUNTIME, // R untime Protocol
.dfu_interface.iInterface = 0x05,
// "DFU Interface"
// ---- FUNCTIONAL DESCRIPTOR for DFU Interface ---.dfu_functional.bLength = 0x09,
.dfu_functional.bDescriptorType = USB_DESCRIPTOR_TYPE_DFU_FUNCTIONAL,
.dfu_functional.bmAttributes = 0x01,
// bitCanDnload
.dfu_functional.wDetatchTimeOut = DFU_TIMEOUT, // suggest 8192ms
.dfu_functional.wTransferSize = DFU_BLOCK_SIZE, // make it 16 bytes
.dfu_functional.bcdDfuVersion = USB_BCD_VERSION_DFU_1_1, // DFU Version 1.1
#endif // DFU
};
3.1.2
DFU Descriptors
If enabled with the DFU macro set to non-zero, the firmware has a device descriptor for the DFU
function. It contains the VID and PID for the DFU function. This may or may not be the same as
the run time VID and PID. In line with the run time configuration this must load the libusb -win32
driver for DFU interface.
USB_device_descriptor device_descriptor_dfumode =
{
.bLength = 0x12,
.bDescriptorType = USB_DESCRIPTOR_TYPE_DEVICE,
.bcdUSB = USB_BCD_VERSION_2_0,
.bDeviceClass = USB_CLASS_DEVICE,
.bDeviceSubClass = USB_SUBCLASS_DEVICE,
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.bDeviceProtocol = USB_PROTOCOL_DEVICE,
.bMaxPacketSize0 = USB_CONTROL_EP_MAX_PACKET_SIZE,
.idVendor = USB_VID_FTDI,
// 0x0403 (FTDI)
.idProduct = DFU_USB_PID_DFUMODE, // 0x0fee
.bcdDevice = 0x0101,
.iManufacturer = 0x01,
.iProduct = 0x04,
.iSerialNumber = 0x03,
.bNumConfigurations = 0x01
};
The configuration descriptor for DFU will contain only an interface descriptor and a functional
descriptor for the DFU interface.
The USB class, subclass and protocol indicate that this device is now in DFU mode.
// Structure containing layout of configuration descriptor
struct config_descriptor_dfumode
{
USB_configuration_descriptor configuration;
USB_interface_descriptor interface;
USB_dfu_functional_descriptor functional;
};
struct config_descriptor_dfumode config_descriptor_dfum ode =
{
.configuration.bLength = 0x09,
.configuration.bDescriptorType = USB_DESCRIPTOR_TYPE_CONFIGURATION,
.configuration.wTotalLength = sizeof(struct config_descriptor_dfumode),
.configuration.bNumInterfaces = 0x01,
.configuration.bConfigurationValue = 0x01,
.configuration.iConfiguration = 0x00,
.configuration.bmAttributes = USB_CONFIG_BMATTRIBUTES_VALUE,
.configuration.bMaxPower = 0xFA, // 500 mA
// ---- INTERFACE DESCRIPTOR for DFU Interface ---.interface.bLength = 0x09,
.interface.bDescriptorType = USB_DESCRIPTOR_TYPE_INTERFACE,
.interface.bInterfaceNumber = DFU_USB_INTERFACE_DFUMODE,
.interface.bAlternateSetting = 0x00,
.interface.bNumEndpoints = 0x00,
.interface.bInterfaceClass = USB_CLASS_APPLICATION, // Application Specific Class
.interface.bInterfaceSubClass = USB_SUBCLASS_DFU,
// Device Firmware Update
.interface.bInterfaceProtocol = USB_PROTOCOL_DFU_DFUMODE, // Runtime Protocol
.interface.iInterface = 0x05, // String 5
// ---- FUNCTIONAL DESCRIPTOR for DFU Interface ---.functional.bLength = 0x09,
.functional.bDescriptorType = USB_DESCRIPTOR_TYPE_DFU_FUNCTIONAL,
.functional.bmAttributes = 0x01, // bitCanDnload
.functional.wDetatchTimeOut = DFU_TIMEOUT, // suggest 8192ms
.functional.wTransferSize = DFU_BLOCK_SIZE,// typically 64 bytes
.functional.bcdDfuVersion = USB_BCD_VERSION_DFU_1_1,
};
The same bmAttributes mask must appear for the DFU functional descriptor in both run time and
DFU modes.
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Descriptor Selection
The standard request handler for GET_DESCRIPTOR requests needs to select the run time or DFU
mode descriptors for device and configuration descriptors. Other descriptors, including the report
descriptors and string descriptors, are not affected.
Determining if the firmware is in run time or DFU mode is achieved by calling the dfu_is_runtime()
function from the DFU library.
A non-zero response will select the run time mode descriptors and a zero response, the DFU mode
descriptors.
FT51A_STATUS standard_req_get_descriptor(USB_device_request *req)
{
uint8_t
*src = NULL;
uint16_t
length = req->wLength;
uint8_t
hValue = req->wValue >> 8;
uint8_t
lValue = req->wValue & 0x00ff;
uint8_t
i, slen;
switch (hValue)
{
case USB_DESCRIPTOR_TYPE_DEVICE:
#ifd DFU
if (dfu_is_runtime())
#endif // DFU
{
src = (char *) &device_descriptor_demo;
}
#if DFU
else
{
src = (char *) &device_descriptor_dfumode;
}
#endif // DFU
if (length > sizeof(USB_device_descriptor)) // too many bytes requested
length = sizeof(USB_device_descriptor); // Entire structure.
break;
case USB_DESCRIPTOR_TYPE_CONFIGURATION:
#if DFU
if (dfu_is_runtime())
#endif // DFU
{
src = (char *) &config_descriptor_demo;
if (length > sizeof(config_descriptor_demo)) //
length = sizeof(config_descriptor_demo); //
}
#if DFU
else
{
src = (char *) &config_descriptor_dfumode;
if (length > sizeof(config_descriptor_dfumode))
length = sizeof(config_descriptor_dfumode);
}
#endif // DFU
break;
too many bytes requested
Entire structure.
// too many bytes requested
// Entire structure.
The FT51A USB library will return the structure pointed to by the standard_req_get_descriptor()
function.
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Note that string descriptor selection is not shown in this code sample.
3.2 USB Class Requests
The firmware is responsible for handling USB class requests. It must determine if the firmware is
in run time or DFU mode and whether a request has been directed to the DFU interface. This must
not interfere with other class requests that may be decoded in the firmware.
The first check is that the class request is aimed at an interface:
FT51A_STATUS class_req_cb(USB_device_request *req)
{
FT51A_STATUS
status = FT51A_FAILED;
uint8_t
interface = LSB(req->wIndex) & 0x0F;
// For DFU requests ensure the recipient is an interface...
if ((req->bmRequestType & USB_BMREQUESTTYPE_RECIPIENT_MASK) ==
USB_BMREQUESTTYPE_RECIPIENT_INTERFACE)
{
If this is correct then the firmware must check if it is in run time or DFU mode before checking the
interface number. The interface number for the DFU mode may differ from that of the run time
mode.
Requests to the DFU interface are passed to the DFU library but others are handled as HID
requests.
#if DFU
// ...and that the interface is the correct Runtime interface
if (dfu_is_runtime())
#endif // DFU
{
#if DFU
if ((interface == DFU_USB_INTERFACE_RUNTIME))
{
// Handle DFU requests DFU_DETATCH, DFU_GETSTATE and DFU_GETSTATUS
// when in run time mode.
switch (req->bRequest)
{
case USB_CLASS_REQUEST_DETACH:
dfu_class_req_detach(req->wValue);
status = FT51A_OK;
break;
case USB_CLASS_REQUEST_GETSTATUS:
dfu_class_req_getstatus();
status = FT51A_OK;
break;
case USB_CLASS_REQUEST_GETSTATE:
dfu_class_req_getstate();
status = FT51A_OK;
break;
}
}
else
#endif // DFU
{
status = FT51A_OK;
// Handle only TMC Class interface requests when not
// in DFU mode.
switch ( req->bRequest)
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{
default:
status = FT51A_FAILED;
break;
case USBTMC_GET_CAPABILITIES:
tmc_class_req_capabilities(0, 0);
break;
case USBTMC_INITIATE_CLEAR:
tmc_class_init_clear();
break;
case USBTMC_CHECK_CLEAR_STATUS:
tmc_class_check_clear();
break;
}
}
}
}
When the device is in DFU mode the DFU request handlers are called as described in the AN 344
DFU Sample.
The TMC class must handle GET_CAPABILITIES, INITIATE_CLEAR and CHECK_CLEAR_STATUS
requests sent to the interface.
Requests sent to a TMC endpoint must also be handled.
// Check for Endpoint recipient
else if((req->bmRequestType & USB_BMREQUESTTYPE_RECIPIENT_MASK) ==
USB_BMREQUESTTYPE_RECIPIENT_ENDPOINT)
{
// TMC class endpoint requests
status = FT51A_OK;
switch ( req->bRequest)
{
default:
status = FT51A_FAILED;
break;
case USBTMC_INITIATE_ABORT_BULK_OUT:
tmc_class_init_abort_bulk_out((req->wValue) & 0xFF, USB_EP_1, USB_DIR_OUT);
break;
case USBTMC_CHECK_ABORT_BULK_OUT_STATUS:
tmc_class_check_abort_bulk_out();
break;
case USBTMC_INITIATE_ABORT_BULK_IN:
tmc_class_init_abort_bulk_in((req->wValue) & 0xFF, USB_EP_1, USB_DIR_IN);
break;
case USBTMC_CHECK_ABORT_BULK_IN_STATUS:
tmc_class_check_abort_bulk_in();
break;
}
}
Each endpoint can receive INITIATE_ABORT_BULK_OUT/IN and CHECK_ABORT_BULK_OUT/IN
requests. These are handled by the TMC library.
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3.3 USB Reset Handler
The reset function handler is used to make the transition from run time mode to DFU mode.
3.4 Timer
A timer is used to provide delays and time measurements for implementing polling intervals.
The first timer ms_timer is used to create general purpose delays, for instance when resetting the
temperature sensor.
Each of the three sensors has a timer forceTimer, tempTimer and pulseTimer. These timers operate
independently.
The DFU also needs a millisecond timer to accurately return to the appIDLE state from the
appDETACH state. The dfu_timer() function in the DFU library, if enabled, should be called every
millisecond to enable this.
void ms_timer_interrupt(const uint8_t flags)
{
(void) flags; // Flags not currently used
if (ms_timer)
{
ms_timer--;
}
#if MEAS_HR
if (pulseTimer)
pulseTimer--;
#endif // MEAS_HR
#if MEAS_TEMP
if (tempTimer)
tempTimer--;
#endif // MEAS_TEMP
#if MEAS_FORCE
if (forceTimer)
forceTimer--;
#endif // MEAS_FORCE
#if DFU
// The DFU detach timer must be called once per millisecond
dfu_timer();
#endif
// Reload the timer
TH0 = MSB(MICROSECONDS_TO_TIMER_TICKS(1000));
TL0 = LSB(MICROSECONDS_TO_TIMER_TICKS(1000));
}
void ms_timer_initialise(void)
{
// Register our own handler for interrupts from Timer 0
interrupts_register(ms_timer_interrupt, interrupts_timer0);
// Timer0 is controlled by TMOD bits 0 to 3, and TCON bits 4 to 5.
TMOD &= 0xF0; // Clear Timer0 bits
TMOD |= 0x01; // Put Timer0 in mode 1 (16 bit)
// Set the count-up value so that it rolls over to 0 after 1 millisecond.
TH0 = MSB(MICROSECONDS_TO_TIMER_TICKS(1000));
TL0 = LSB(MICROSECONDS_TO_TIMER_TICKS(1000));
TCON &= 0xCF; // Clear Timer0's Overflow and Run flags
TCON |= 0x10; // Start Timer0 (set its Run flag)
}
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3.5 TMC Messages
The TMC application will receive TMC messages from the TMC library.
In the main loop of the application there is a call to the TMC_process() function. This will check for
messages received from the LabView application (TMCApp.exe) running on the host PC and
process them. Messages are decoded by a callback into the application from the library. The
callbacks are setup when initialising the TMC library:
tmc_ctx.message_cmd_cb = tmc_command_cb;
tmc_ctx.message_rsp_cb = tmc_response_cb;
// Initialise the TMC interface
tmc_initialise(&tmc_ctx);
The callback function tmc_command_cb() will decode the incoming command from a TMC Device
Dependent Message Out. In this case the message is an SCPI command from the SCPI_cmds table.
There is a matching table called scpi_cmd_list which contains pointers to handler functions to
perform the required operation.
The SCPI_cmds and scpi_cmd_list tables are shown below. Additional commands and handlers can
be added to support more SCPI commands.
__code char *SCPI_cmds[] = {
"*IDN?\n",
#if MEAS_HR
"*MEAS:hrm?\n",
#endif
#if MEAS_FORCE
"*MEAS:for?\n",
#endif
#if MEAS_TEMP
"*MEAS:tmp?\n",
#endif
NULL,
};
__code SCPI_CMD_t scpi_cmd_list[] =
{
scpi_cmd_identify_query, // *IDN?
#if MEAS_HR
scpi_cmd_meas_hr, // *MEAS:hrm?
#endif
#if MEAS_FORCE
scpi_cmd_meas_force, // *MEAS:for?
#endif
#if MEAS_TEMP
scpi_cmd_meas_temp, // *MEAS:tmp?
#endif
NULL,
};
In our implementation the SCPI command handler functions generate a response string from the
latest measurements from the sensors. This is kept until the LabView application (TMCApp.exe)
running on the host PC reads the response back with a TMC Device Depend ent Message In.
The tmc_response_cb() callback function will copy the response string into the message sent back
to the TMC application on the host.
This simple method of parsing TMC messages provides adequate coverage to allow a LabView
application to use the VISA interface to access TMC devices, without adding too much code to the
TMC firmware.
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Note that there is neither, verification of bTag values in the TMC messages nor any method of
satisfying multiple concurrent SCPI commands. A TMC application or LabView application can be
written to avoid such overlapping messages.
3.6 Sensor Reading Acquisition
Each sensor is read from the firmware’s main loop.
3.6.1
Force Sensor
When the forceTimer reaches zero then a new ADC is triggered and the timer restarted. The ADC
conversion will take place in the background and an interrupt generated when it is complete.
if (forceTimer == 0)
{
IO_REG_INTERRUPTS_WRITE(IO_CELL_SAMPLE_0_7_1, MASK_IO_CELL_0_SAMPLE);
forceTimer = FORCE_TIMER;
}
The ADC interrupt handler (section below) will update the forceSample and forceSampleReady
variables when the reading is complete.
IO_REG_INTERRUPTS_READ(IO_CELL_INT_0_1, interrupt);
// FSR Output
if (interrupt & MASK_SD_CELL_0_INT)
{
IO_REG_INTERRUPTS_READ(IO_CELL_0_ADC_DATA_L_1, sample_l);
IO_REG_INTERRUPTS_READ(IO_CELL_0_ADC_DATA_U_1, sample_h);
forceSample = ((sample_h << 8) | sample_l);
forceSampleReady = TRUE;
// Clear ADC interrupt register bit
IO_REG_INTERRUPTS_WRITE(IO_CELL_INT_0_1, MASK_SD_CELL_0_INT);
}
The main loop will arrive back at the force sensor code and update the force reading when the
forceSampleReady flag is set by the interrupt handler.
if (forceSampleReady)
{
forceSampleReady = FALSE;
if (forceSample > 900)
{
forceSample = 900;
}
force = forceSample;
}
The forceTimer will continue to run until the next sample is due.
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Heart Rate Sensor
When the pulseTimer reaches zero then a new ADC is triggered and the timer restarted. The ADC
conversion will take place in the background and an interrupt generated when it is complete.
if (pulseTimer == 0)
{
IO_REG_INTERRUPTS_WRITE(IO_CELL_SAMPLE_8_15_1, MASK_IO_CELL_10_SAMPLE);
pulseTimer = PULSE_TIMER;
}
The ADC interrupt handler will update the pulseSample and pulseSampleReady variables when the
reading is complete.
IO_REG_INTERRUPTS_READ(IO_CELL_INT_1_1, interrupt);
// Pulse Rate
if (interrupt & MASK_SD_CELL_10_INT)
{
IO_REG_INTERRUPTS_READ(IO_CELL_10_ADC_DATA_L_1, sample_l);
IO_REG_INTERRUPTS_READ(IO_CELL_10_ADC_DATA_U_1, sample_h);
pulseSample = ((sample_h << 8) | sample_l);
pulseSampleReady = TRUE;
// Clear ADC interrupt register bit
IO_REG_INTERRUPTS_WRITE(IO_CELL_INT_1_1, MASK_SD_CELL_10_INT);
}
The main loop will arrive back at the heart rate sensor code and updat e the heart beat reading
when the pulseSampleReady flag is set by the interrupt handler.
if (pulseTimer == 0)
{
IO_REG_INTERRUPTS_WRITE(IO_CELL_SAMPLE_8_15_1, MASK_IO_CELL_10_SAMPLE);
pulseTimer = PULSE_TIMER;
}
if (pulseSampleReady)
{
pulseSampleReady = FALSE;
if (pulseSample > 0xff)
pulseSample = 0xff;
pulseSamples[pulseIndexer] = pulseSample;
// Count the total number of beats (for the entire sample period) ...
heartRate = 0;
pulseCounterHystRising = pulseCounterHystFalling = 0;
for (j = 0; j < PULSE_SAMPLES; j++)
{
if (pulseSamples[j] > PULSE_THRESHOLD)
{
// Look for PULSE_IS_BEAT samples in a row to be above the
// threshold.
pulseCounterHystRising++;
if (pulseCounterHystRising == PULSE_IS_BEAT)
{
pulseCounterHystFalling = PULSE_IS_BEAT;
heartRate++;
}
}
else
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{
if (pulseCounterHystFalling)
{
pulseCounterHystFalling--;
pulseCounterHystRising = 0;
}
}
}
// Correct for sample array size. i.e. 600 samples at 25ms intervals
// will be 15 seconds of data. So multiply by 60/15 = 4 times to get
// pulse per minute.
heartRate *= (60000 / (PULSE_SAMPLES * PULSE_TIMER));
pulseIndexer = (++pulseIndexer) % PULSE_SAMPLES;
}
The loop fills a buffer with PULSE_SAMPLES number of samples of the converted analogue voltage
from the heart rate circuit. It then parses the buffer to identify a certain number of consecutive
samples above or below a threshold value of PULSE_THRESHOLD. Each of these transitions is
regarded as a detected heartbeat. The final operation is to count these heartbeats and convert the
result into beats per minute.
3.6.2
Temperature Sensor
An SPI bus is used to measure the temperature from an ADT7310 sensor connected to the SPI
Master interface. When the tempTimer reaches zero the timer is reset and an SPI Master read is
performed to the ADT3710.
if (tempTimer == 0)
{
// Read the temperature from the SPI Master
temperature = temperature_read();
tempTimer = TEMP_TIMER;
}
The temperature is returned in units of 0.01 °C.
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4 LabView Application
The LabView application uses the National Instruments VISA driver to communicate with the TMC
Firmware.
Provided is a pre-compiled application which will display the readings obtained from the FT51A
EVM modules in a chart and as dials. The source code form is provided as well.
4.1 Requirements
Serial numbers for each FT51A EVM module running the firmware must be unique. The FT51
Software Development Kit has a command line utility called FT51Astr.exe that can alter string
descriptors. String number 3 in the string descriptor table in the Test and Measurement firmware
contains the serial number.
For each FT51A EVM module, modify a copy of the original firmware IHX file with the FT51Astr.exe
utility to change string 3 to a unique value and program that onto the module.
C:\workspace\tmc_app\Debug>ft51str -v -3 "NI-VISA-42422-b" tmc_app.ihx
Reading input file tmc_app.ihx ... done
Finding strings ....... done
String table size 0x9E bytes with 7 entries
Modifying string 3 to "NI-VISA-42422-b"
Finding string 3 ... done
Writing replacement string ............... done
Writing tmc_app.ihx.mod ... done
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5 Possible Improvements
It would be possible to implement a different method of handling the messages, potentially
starting to acquire sample s in a handler function when called through tmc_command_cb() then
formatting the result in a new handler called from tmc_response_cb(). This would be useful in
situations w here a result cannot be continually updated or the time taken to formulate a response
is relatively long, either due to sampling periods or the length of time that some hardware takes to
respond.
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6 Contact Information
Head Office – Glasgow, UK
Branch Office – Tigard, Oregon, USA
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Unit 1, 2 Seaward Place, Centurion Business Park
Glasgow G41 1HH
United Kingdom
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Future Technology Devices International Limited
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Distributor and Sales Representatives
Please visit the Sales Network page of the FTDI Web site for the contact details of our distributor(s) and sales
representative(s) in your country.
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Appendix A – References
Document References
FTDI MCU web page: http://www.ftdichip.com/MCU.html
USB Test and Measurement Class specification:
http://www.usb.org/developers/docs/devclass_docs/USBTMC_1_006a.zip
IVI Foundation: http://www.ivifoundation.org/
SCPI specification: http://www.ivifoundation.org/docs/scpi-99.pdf
USB Device Firmware Update Class specification:
http://www.usb.org/developers/docs/devclass_docs/DFU_1.1.pdf
Acronyms and Abbreviations
Terms
Description
HID
Human Interface Device
MTP
Multiple Time Program – non-volatile memory used to store program code
on the FT51A.
SCPI
Standard Commands for Programmable Instruments
TMC
Test and Measurement Class
USB
Universal Serial Bus
USB-IF
VISA
USB Implementers Forum
Virtual Instruments Software Architecture
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Appendix B – List of Tables & Figures
List of Figures
Figure 2.2-1 LabVIEW Run-Time Engine Alert Dialog Box .............................................................. 6
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Appendix C – Revision History
Document Title:
AN_347 FT51A Test and Measurement Sample
Document Reference No.:
FT_001124
Clearance No.:
FTDI# 432
Product Page:
http://www.ftdichip.com/FTProducts.htm
Document Feedback:
Send Feedback
Revision
Changes
Date
1.0
Initial Release
2014-12-12
1.1
Update FT51 references to FT51A
2015-11-26
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