ftdi MPSSE / jtag: add option to use neg edge for TDO's sampling

README.md

@@ -54,6 +54,8 @@ openFPGALoader -- a program to flash FPGA
       --bitstream arg       bitstream
   -b, --board arg           board name, may be used instead of cable
   -c, --cable arg           jtag interface
+      --invert-read-edge    JTAG mode / FTDI: read on negative edge instead
+                            of positive
       --vid arg             probe Vendor ID
       --pid arg             probe Product ID
       --ftdi-serial arg     FTDI chip serial number

doc/guide/advanced.rst

@@ -10,6 +10,15 @@ Resetting an FPGA
 
     openFPGALoader [options] -r
 
+Using negative edge for TDO's sampling
+====================================
+
+If transaction are unstable you can try to change read edge by using
+
+.. code-block:: bash
+
+    openFPGALoader [options] --invert-read-edge
+
 Reading the bitstream from STDIN
 ================================
 

src/ftdiJtagMPSSE.cpp

@@ -29,10 +29,12 @@ using namespace std;
 #endif
 
 FtdiJtagMPSSE::FtdiJtagMPSSE(const FTDIpp_MPSSE::mpsse_bit_config &cable,
-			string dev, const string &serial, uint32_t clkHZ, int8_t verbose):
+			string dev, const string &serial, uint32_t clkHZ,
+			bool invert_read_edge, int8_t verbose):
 			FTDIpp_MPSSE(cable, dev, serial, clkHZ, verbose), _ch552WA(false),
 			_write_mode(MPSSE_WRITE_NEG),  // always write on neg edge
-			_read_mode(0)
+			_read_mode(0),
+			_invert_read_edge(invert_read_edge) // false: pos, true: neg
 {
 	init_internal(cable);
 }
@@ -88,10 +90,10 @@ void FtdiJtagMPSSE::config_edge()
 {
 	/* at high (>15MHz) with digilent cable (arty)
 	 * opposite edges must be used.
-	 * Not required with classic FT2232
+	 * Not required with classic FT2232 but user selectable
 	 */
-	if (FTDIpp_MPSSE::getClkFreq() >= 15000000 &&
-			!strncmp((const char *)_iproduct, "Digilent USB Device", 19)) {
+	if (_invert_read_edge || (FTDIpp_MPSSE::getClkFreq() >= 15000000 &&
+			!strncmp((const char *)_iproduct, "Digilent USB Device", 19))) {
 		_read_mode = MPSSE_READ_NEG;
 	} else {
 		_read_mode = 0;

src/ftdiJtagMPSSE.hpp

@@ -23,7 +23,8 @@
 class FtdiJtagMPSSE : public JtagInterface, public FTDIpp_MPSSE {
  public:
 	FtdiJtagMPSSE(const FTDIpp_MPSSE::mpsse_bit_config &cable, std::string dev,
-		const std::string &serial, uint32_t clkHZ, int8_t verbose = 0);
+		const std::string &serial, uint32_t clkHZ, bool invert_read_edge,
+		int8_t verbose = 0);
 	virtual ~FtdiJtagMPSSE();
 
 	int setClkFreq(uint32_t clkHZ) override;
@@ -58,5 +59,6 @@ class FtdiJtagMPSSE : public JtagInterface, public FTDIpp_MPSSE {
 	bool _ch552WA; /* avoid errors with SiPeed tangNano */
 	uint8_t _write_mode; /**< write edge configuration */
 	uint8_t _read_mode; /**< read edge configuration */
+	bool _invert_read_edge; /**< read edge selection (false: pos, true: neg) */
 };
 #endif

src/jtag.cpp

@@ -63,13 +63,14 @@ using namespace std;
 
 Jtag::Jtag(cable_t &cable, const jtag_pins_conf_t *pin_conf, string dev,
 			const string &serial, uint32_t clkHZ, int8_t verbose,
-			const string &firmware_path):
+			const bool invert_read_edge, const string &firmware_path):
 			_verbose(verbose),
 			_state(RUN_TEST_IDLE),
 			_tms_buffer_size(128), _num_tms(0),
 			_board_name("nope"), device_index(0)
 {
-	init_internal(cable, dev, serial, pin_conf, clkHZ, firmware_path);
+	init_internal(cable, dev, serial, pin_conf, clkHZ, firmware_path,
+			invert_read_edge);
 	detectChain(5);
 }
 
@@ -80,7 +81,8 @@ Jtag::~Jtag()
 }
 
 void Jtag::init_internal(cable_t &cable, const string &dev, const string &serial,
-	const jtag_pins_conf_t *pin_conf, uint32_t clkHZ, const string &firmware_path)
+	const jtag_pins_conf_t *pin_conf, uint32_t clkHZ, const string &firmware_path,
+	const bool invert_read_edge)
 {
 	switch (cable.type) {
 	case MODE_ANLOGICCABLE:
@@ -92,7 +94,8 @@ void Jtag::init_internal(cable_t &cable, const string &dev, const string &serial
 		_jtag = new FtdiJtagBitBang(cable.config, pin_conf, dev, serial, clkHZ, _verbose);
 		break;
 	case MODE_FTDI_SERIAL:
-		_jtag = new FtdiJtagMPSSE(cable.config, dev, serial, clkHZ, _verbose);
+		_jtag = new FtdiJtagMPSSE(cable.config, dev, serial, clkHZ,
+				invert_read_edge, _verbose);
 		break;
 	case MODE_CH552_JTAG:
 		_jtag = new CH552_jtag(cable.config, dev, serial, clkHZ, _verbose);

src/jtag.hpp

@@ -19,6 +19,7 @@ class Jtag {
  public:
 	Jtag(cable_t &cable, const jtag_pins_conf_t *pin_conf, std::string dev,
 		const std::string &serial, uint32_t clkHZ, int8_t verbose = 0,
+		const bool invert_read_edge = false,
 		const std::string &firmware_path = "");
 	~Jtag();
 
@@ -105,7 +106,8 @@ class Jtag {
 	void init_internal(cable_t &cable, const std::string &dev,
 		const std::string &serial,
 		const jtag_pins_conf_t *pin_conf, uint32_t clkHZ,
-		const std::string &firmware_path);
+		const std::string &firmware_path,
+		const bool invert_read_edge);
 	/*!
 	 * \brief search in fpga_list and misc_dev_list for a device with idcode
 	 *        if found insert idcode and irlength in _devices_list and

src/main.cpp

@@ -45,6 +45,7 @@ struct arguments {
 	string ftdi_serial;
 	int ftdi_channel;
 	uint32_t freq;
+	bool invert_read_edge;
 	string board;
 	bool pin_config;
 	bool list_cables;
@@ -80,7 +81,7 @@ int main(int argc, char **argv)
 
 	/* command line args. */
 	struct arguments args = {0, false, false, false, 0, "", "", "-", "", -1,
-			0, "-", false, false, false, false, Device::PRG_NONE, false,
+			0, false, "-", false, false, false, false, Device::PRG_NONE, false,
 			false, false, "", "", "", -1, 0, false, -1, 0, 0, 0, false, ""};
 	/* parse arguments */
 	try {
@@ -369,7 +370,8 @@ int main(int argc, char **argv)
 	Jtag *jtag;
 	try {
 		jtag = new Jtag(cable, &pins_config, args.device, args.ftdi_serial,
-				args.freq, args.verbose, args.probe_firmware);
+				args.freq, args.verbose, args.invert_read_edge,
+				args.probe_firmware);
 	} catch (std::exception &e) {
 		printError("JTAG init failed with: " + string(e.what()));
 		return EXIT_FAILURE;
@@ -579,6 +581,8 @@ int parse_opt(int argc, char **argv, struct arguments *args, jtag_pins_conf_t *p
 			("b,board",     "board name, may be used instead of cable",
 				cxxopts::value<string>(args->board))
 			("c,cable", "jtag interface", cxxopts::value<string>(args->cable))
+			("invert-read-edge", "JTAG mode / FTDI: read on negative edge instead of positive",
+				cxxopts::value<bool>(args->invert_read_edge))
 			("vid", "probe Vendor ID", cxxopts::value<uint16_t>(args->vid))
 			("pid", "probe Product ID", cxxopts::value<uint16_t>(args->pid))