diff --git a/dediprog.c b/dediprog.c
index 996d2d7..d18ce36 100644
--- a/dediprog.c
+++ b/dediprog.c
@@ -40,7 +40,7 @@
 
 #define FIRMWARE_VERSION(x,y,z) ((x << 16) | (y << 8) | z)
 #define DEFAULT_TIMEOUT 3000
-#define REQTYPE_OTHER_OUT (USB_ENDPOINT_IN | USB_TYPE_VENDOR | USB_RECIP_OTHER)		/* 0x43 */
+#define REQTYPE_OTHER_OUT (USB_ENDPOINT_OUT | USB_TYPE_VENDOR | USB_RECIP_OTHER)	/* 0x43 */
 #define REQTYPE_OTHER_IN (USB_ENDPOINT_IN | USB_TYPE_VENDOR | USB_RECIP_OTHER)		/* 0xC3 */
 #define REQTYPE_EP_OUT (USB_ENDPOINT_OUT | USB_TYPE_VENDOR | USB_RECIP_ENDPOINT)	/* 0x42 */
 #define REQTYPE_EP_IN (USB_ENDPOINT_IN | USB_TYPE_VENDOR | USB_RECIP_ENDPOINT)		/* 0xC2 */
@@ -120,9 +120,9 @@
 	WRITE_MODE_128B_PAGE			= 5,
 	WRITE_MODE_PAGE_AT26DF041		= 6,
 	WRITE_MODE_SILICON_BLUE_FPGA		= 7,
-	WRITE_MODE_64B_PAGE_NUMONYX_PCM		= 8,	/* unit of length 512 bytes */
+	WRITE_MODE_64B_PAGE_NUMONYX_PCM		= 8,	/* unit of 512 bytes */
 	WRITE_MODE_4B_ADDR_256B_PAGE_PGM	= 9,
-	WRITE_MODE_32B_PAGE_PGM_MXIC_512K	= 10,	/* unit of length 512 bytes */
+	WRITE_MODE_32B_PAGE_PGM_MXIC_512K	= 10,	/* unit of 512 bytes */
 	WRITE_MODE_4B_ADDR_256B_PAGE_PGM_0x12	= 11,
 	WRITE_MODE_4B_ADDR_256B_PAGE_PGM_FLAGS	= 12,
 };
@@ -130,16 +130,26 @@
 
 static int dediprog_firmwareversion = FIRMWARE_VERSION(0, 0, 0);
 
-#if 0
-/* Might be useful for other pieces of code as well. */
-static void print_hex(void *buf, size_t len)
+/* Returns true if firmware (and thus hardware) supports the "new" protocol */
+static bool is_new_prot(void)
 {
-	size_t i;
-
-	for (i = 0; i < len; i++)
-		msg_pdbg(" %02x", ((uint8_t *)buf)[i]);
+	/* if (SF100) */
+	return dediprog_firmwareversion >= FIRMWARE_VERSION(5, 5, 0);
+	/* else if (SF600)
+	return dediprog_firmwareversion >= FIRMWARE_VERSION(6, 9, 0); */
 }
-#endif
+
+static int dediprog_read(enum dediprog_cmds cmd, unsigned int value, unsigned int idx, uint8_t *bytes, size_t size)
+{
+	return usb_control_msg(dediprog_handle, REQTYPE_EP_IN, cmd, value, idx,
+			       (char *)bytes, size, DEFAULT_TIMEOUT);
+}
+
+static int dediprog_write(enum dediprog_cmds cmd, unsigned int value, unsigned int idx, const uint8_t *bytes, size_t size)
+{
+	return usb_control_msg(dediprog_handle, REQTYPE_EP_OUT, cmd, value, idx,
+			       (char *)bytes, size, DEFAULT_TIMEOUT);
+}
 
 /* Might be useful for other USB devices as well. static for now. */
 /* device parameter allows user to specify one device of multiple installed */
@@ -166,24 +176,30 @@
 	if (leds < LED_NONE || leds > LED_ALL)
 		leds = LED_ALL;
 
-	/* Older Dediprogs with 2.x.x and 3.x.x firmware only had
-	 * two LEDs, and they were reversed. So map them around if 
-	 * we have an old device. On those devices the LEDs map as
-	 * follows:
+	/* Older Dediprogs with 2.x.x and 3.x.x firmware only had two LEDs, assigned to different bits. So map
+	 * them around if we have an old device. On those devices the LEDs map as follows:
 	 *   bit 2 == 0: green light is on.
-	 *   bit 0 == 0: red light is on. 
+	 *   bit 0 == 0: red light is on.
+	 *
+	 * Additionally, the command structure has changed with the "new" protocol.
+	 *
+	 * FIXME: take IO pins into account
 	 */
-	int target_leds;
-	if (dediprog_firmwareversion < FIRMWARE_VERSION(5,0,0)) {
-		target_leds = ((leds & LED_ERROR) >> 2) |
-			((leds & LED_PASS) << 2);
+	int target_leds, ret;
+	if (is_new_prot()) {
+		target_leds = (leds ^ 7) << 8;
+		ret = dediprog_write(CMD_SET_IO_LED, target_leds, 0, NULL, 0);
 	} else {
-		target_leds = leds;
+		if (dediprog_firmwareversion < FIRMWARE_VERSION(5, 0, 0)) {
+			target_leds = ((leds & LED_ERROR) >> 2) | ((leds & LED_PASS) << 2);
+		} else {
+			target_leds = leds;
+		}
+		target_leds ^= 7;
+
+		ret = dediprog_write(CMD_SET_IO_LED, 0x9, target_leds, NULL, 0);
 	}
 
-	target_leds ^= 7;
-	int ret = usb_control_msg(dediprog_handle, REQTYPE_EP_OUT, CMD_SET_IO_LED, 0x09, target_leds,
-				  NULL, 0x0, DEFAULT_TIMEOUT);
 	if (ret != 0x0) {
 		msg_perr("Command Set LED 0x%x failed (%s)!\n", leds, usb_strerror());
 		return 1;
@@ -222,8 +238,7 @@
 		/* Wait some time as the original driver does. */
 		programmer_delay(200 * 1000);
 	}
-	ret = usb_control_msg(dediprog_handle, REQTYPE_EP_OUT, CMD_SET_VCC, voltage_selector, 0,
-			      NULL, 0x0, DEFAULT_TIMEOUT);
+	ret = dediprog_write(CMD_SET_VCC, voltage_selector, 0, NULL, 0);
 	if (ret != 0x0) {
 		msg_perr("Command Set SPI Voltage 0x%x failed!\n",
 			 voltage_selector);
@@ -263,8 +278,7 @@
 	const struct dediprog_spispeeds *spispeed = &spispeeds[spispeed_idx];
 	msg_pdbg("SPI speed is %sHz\n", spispeed->name);
 
-	int ret = usb_control_msg(dediprog_handle, REQTYPE_EP_OUT, CMD_SET_SPI_CLK, spispeed->speed, 0xff,
-				  NULL, 0x0, DEFAULT_TIMEOUT);
+	int ret = dediprog_write(CMD_SET_SPI_CLK, spispeed->speed, 0, NULL, 0);
 	if (ret != 0x0) {
 		msg_perr("Command Set SPI Speed 0x%x failed!\n", spispeed->speed);
 		return 1;
@@ -272,52 +286,66 @@
 	return 0;
 }
 
+static void fill_rw_cmd_payload(uint8_t *data_packet, unsigned int count, uint8_t dedi_spi_cmd, unsigned int *value, unsigned int *idx, unsigned int start) {
+	/* First 5 bytes are common in both generations. */
+	data_packet[0] = count & 0xff;
+	data_packet[1] = (count >> 8) & 0xff;
+	data_packet[2] = 0; /* RFU */
+	data_packet[3] = dedi_spi_cmd; /* Read/Write Mode (currently READ_MODE_STD, WRITE_MODE_PAGE_PGM or WRITE_MODE_2B_AAI) */
+	data_packet[4] = 0; /* "Opcode". Specs imply necessity only for READ_MODE_4B_ADDR_FAST and WRITE_MODE_4B_ADDR_256B_PAGE_PGM */
+
+	if (is_new_prot()) {
+		*value = *idx = 0;
+		data_packet[5] = 0; /* RFU */
+		data_packet[6] = (start >>  0) & 0xff;
+		data_packet[7] = (start >>  8) & 0xff;
+		data_packet[8] = (start >> 16) & 0xff;
+		data_packet[9] = (start >> 24) & 0xff;
+	} else {
+		*value = start % 0x10000;
+		*idx = start / 0x10000;
+	}
+}
+
 /* Bulk read interface, will read multiple 512 byte chunks aligned to 512 bytes.
  * @start	start address
  * @len		length
  * @return	0 on success, 1 on failure
  */
-static int dediprog_spi_bulk_read(struct flashctx *flash, uint8_t *buf,
-				  unsigned int start, unsigned int len)
+static int dediprog_spi_bulk_read(struct flashctx *flash, uint8_t *buf, unsigned int start, unsigned int len)
 {
-	int ret;
-	unsigned int i;
 	/* chunksize must be 512, other sizes will NOT work at all. */
-	const unsigned int chunksize = 0x200;
+	const unsigned int chunksize = 512;
 	const unsigned int count = len / chunksize;
-	const char count_and_chunk[] = {count & 0xff,
-					(count >> 8) & 0xff,
-					chunksize & 0xff,
-					(chunksize >> 8) & 0xff};
 
 	if ((start % chunksize) || (len % chunksize)) {
-		msg_perr("%s: Unaligned start=%i, len=%i! Please report a bug "
-			 "at flashrom@flashrom.org\n", __func__, start, len);
+		msg_perr("%s: Unaligned start=%i, len=%i! Please report a bug at flashrom@flashrom.org\n",
+			 __func__, start, len);
 		return 1;
 	}
 
-	/* No idea if the hardware can handle empty reads, so chicken out. */
-	if (!len)
+	if (len == 0)
 		return 0;
-	/* Command Read SPI Bulk. No idea which read command is used on the
-	 * SPI side.
-	 */
-	ret = usb_control_msg(dediprog_handle, REQTYPE_EP_OUT, CMD_READ, start % 0x10000,
-			      start / 0x10000, (char *)count_and_chunk,
-			      sizeof(count_and_chunk), DEFAULT_TIMEOUT);
-	if (ret != sizeof(count_and_chunk)) {
-		msg_perr("Command Read SPI Bulk failed, %i %s!\n", ret,
-			 usb_strerror());
+
+	/* Command packet size of protocols: new 10 B, old 5 B. */
+	uint8_t data_packet[is_new_prot() ? 10 : 5];
+	unsigned int value, idx;
+	fill_rw_cmd_payload(data_packet, count, READ_MODE_STD, &value, &idx, start);
+
+	int ret = dediprog_write(CMD_READ, value, idx, data_packet, sizeof(data_packet));
+	if (ret != sizeof(data_packet)) {
+		msg_perr("Command Read SPI Bulk failed, %i %s!\n", ret, usb_strerror());
 		return 1;
 	}
 
+	unsigned int i;
 	for (i = 0; i < count; i++) {
 		ret = usb_bulk_read(dediprog_handle, 0x80 | dediprog_endpoint,
 				    (char *)buf + i * chunksize, chunksize,
 				    DEFAULT_TIMEOUT);
 		if (ret != chunksize) {
-			msg_perr("SPI bulk read %i failed, expected %i, got %i "
-				 "%s!\n", i, chunksize, ret, usb_strerror());
+			msg_perr("SPI bulk read %i failed, expected %i, got %i %s!\n",
+				 i, chunksize, ret, usb_strerror());
 			return 1;
 		}
 	}
@@ -325,8 +353,7 @@
 	return 0;
 }
 
-static int dediprog_spi_read(struct flashctx *flash, uint8_t *buf,
-			     unsigned int start, unsigned int len)
+static int dediprog_spi_read(struct flashctx *flash, uint8_t *buf, unsigned int start, unsigned int len)
 {
 	int ret;
 	/* chunksize must be 512, other sizes will NOT work at all. */
@@ -346,13 +373,12 @@
 
 	/* Round down. */
 	bulklen = (len - residue) / chunksize * chunksize;
-	ret = dediprog_spi_bulk_read(flash, buf + residue, start + residue,
-				     bulklen);
+	ret = dediprog_spi_bulk_read(flash, buf + residue, start + residue, bulklen);
 	if (ret)
 		goto err;
 
 	len -= residue + bulklen;
-	if (len) {
+	if (len != 0) {
 		msg_pdbg("Slow read for partial block from 0x%x, length 0x%x\n",
 			 start, len);
 		ret = spi_read_chunked(flash, buf + residue + bulklen,
@@ -378,15 +404,11 @@
 static int dediprog_spi_bulk_write(struct flashctx *flash, const uint8_t *buf, unsigned int chunksize,
 				   unsigned int start, unsigned int len, uint8_t dedi_spi_cmd)
 {
-	int ret;
-	unsigned int i;
 	/* USB transfer size must be 512, other sizes will NOT work at all.
 	 * chunksize is the real data size per USB bulk transfer. The remaining
 	 * space in a USB bulk transfer must be filled with 0xff padding.
 	 */
 	const unsigned int count = len / chunksize;
-	const char count_and_cmd[] = {count & 0xff, (count >> 8) & 0xff, 0x00, dedi_spi_cmd};
-	char usbbuf[512];
 
 	/*
 	 * We should change this check to
@@ -406,28 +428,28 @@
 	}
 
 	/* No idea if the hardware can handle empty writes, so chicken out. */
-	if (!len)
+	if (len == 0)
 		return 0;
-	/* Command Write SPI Bulk. No idea which write command is used on the
-	 * SPI side.
-	 */
-	ret = usb_control_msg(dediprog_handle, REQTYPE_EP_OUT, CMD_WRITE, start % 0x10000, start / 0x10000,
-			      (char *)count_and_cmd, sizeof(count_and_cmd), DEFAULT_TIMEOUT);
-	if (ret != sizeof(count_and_cmd)) {
+
+	/* Command packet size of protocols: new 10 B, old 5 B. */
+	uint8_t data_packet[is_new_prot() ? 10 : 5];
+	unsigned int value, idx;
+	fill_rw_cmd_payload(data_packet, count, dedi_spi_cmd, &value, &idx, start);
+	int ret = dediprog_write(CMD_WRITE, value, idx, data_packet, sizeof(data_packet));
+	if (ret != sizeof(data_packet)) {
 		msg_perr("Command Write SPI Bulk failed, %i %s!\n", ret,
 			 usb_strerror());
 		return 1;
 	}
 
+	unsigned int i;
 	for (i = 0; i < count; i++) {
-		memset(usbbuf, 0xff, sizeof(usbbuf));
+		char usbbuf[512];
 		memcpy(usbbuf, buf + i * chunksize, chunksize);
-		ret = usb_bulk_write(dediprog_handle, dediprog_endpoint,
-				    usbbuf, 512,
-				    DEFAULT_TIMEOUT);
+		memset(usbbuf + chunksize, 0xff, sizeof(usbbuf) - chunksize); // fill up with 0xFF
+		ret = usb_bulk_write(dediprog_handle, dediprog_endpoint, usbbuf, 512, DEFAULT_TIMEOUT);
 		if (ret != 512) {
-			msg_perr("SPI bulk write failed, expected %i, got %i "
-				 "%s!\n", 512, ret, usb_strerror());
+			msg_perr("SPI bulk write failed, expected %i, got %i %s!\n", 512, ret, usb_strerror());
 			return 1;
 		}
 	}
@@ -506,30 +528,45 @@
 	int ret;
 
 	msg_pspew("%s, writecnt=%i, readcnt=%i\n", __func__, writecnt, readcnt);
-	if (writecnt > UINT16_MAX) {
+	if (writecnt > flash->mst->spi.max_data_write) {
 		msg_perr("Invalid writecnt=%i, aborting.\n", writecnt);
 		return 1;
 	}
-	if (readcnt > UINT16_MAX) {
+	if (readcnt > flash->mst->spi.max_data_read) {
 		msg_perr("Invalid readcnt=%i, aborting.\n", readcnt);
 		return 1;
 	}
 	
-	ret = usb_control_msg(dediprog_handle, REQTYPE_EP_OUT, CMD_TRANSCEIVE, 0, readcnt ? 0x1 : 0x0,
-			      (char *)writearr, writecnt, DEFAULT_TIMEOUT);
+	unsigned int idx, value;
+	/* New protocol has options and timeout combined as value while the old one used the value field for
+	 * timeout and the index field for options. */
+	if (is_new_prot()) {
+		idx = 0;
+		value = readcnt ? 0x1 : 0x0; // Indicate if we require a read
+	} else {
+		idx = readcnt ? 0x1 : 0x0; // Indicate if we require a read
+		value = 0;
+	}
+	ret = dediprog_write(CMD_TRANSCEIVE, value, idx, writearr, writecnt);
 	if (ret != writecnt) {
 		msg_perr("Send SPI failed, expected %i, got %i %s!\n",
 			 writecnt, ret, usb_strerror());
 		return 1;
 	}
-	if (readcnt == 0)
+	if (readcnt == 0) // If we don't require a response, we are done here
 		return 0;
 
-	ret = usb_control_msg(dediprog_handle, REQTYPE_EP_IN, CMD_TRANSCEIVE, 0, 0,
-			     (char *)readarr, readcnt, DEFAULT_TIMEOUT);
+	const uint8_t read_timeout = 10 + readcnt/512;
+	if (is_new_prot()) {
+		idx = 0;
+		value = min(read_timeout, 0xFF) | (0 << 8) ; // Timeout in lower byte, option in upper byte
+	} else {
+		idx = (0 & 0xFF);  // Lower byte is option (0x01 = require SR, 0x02 keep CS low)
+		value = min(read_timeout, 0xFF); // Possibly two bytes but we play safe here
+	}
+	ret = dediprog_read(CMD_TRANSCEIVE, value, idx, readarr, readcnt);
 	if (ret != readcnt) {
-		msg_perr("Receive SPI failed, expected %i, got %i %s!\n",
-			 readcnt, ret, usb_strerror());
+		msg_perr("Receive SPI failed, expected %i, got %i %s!\n", readcnt, ret, usb_strerror());
 		return 1;
 	}
 	return 0;
@@ -541,20 +578,8 @@
 	int fw[3];
 	char buf[0x11];
 
-#if 0
-	/* Command Prepare Receive Device String. */
-	ret = usb_control_msg(dediprog_handle, REQTYPE_OTHER_IN, 0x7, 0x0, 0xef03,
-			      buf, 0x1, DEFAULT_TIMEOUT);
-	/* The char casting is needed to stop gcc complaining about an always true comparison. */
-	if ((ret != 0x1) || (buf[0] != (char)0xff)) {
-		msg_perr("Unexpected response to Command Prepare Receive Device"
-			 " String!\n");
-		return 1;
-	}
-#endif
 	/* Command Receive Device String. */
-	ret = usb_control_msg(dediprog_handle, REQTYPE_EP_IN, CMD_READ_PROG_INFO, 0, 0,
-			      buf, 0x10, DEFAULT_TIMEOUT);
+	ret = dediprog_read(CMD_READ_PROG_INFO, 0, 0, (uint8_t *)buf, 0x10);
 	if (ret != 0x10) {
 		msg_perr("Incomplete/failed Command Receive Device String!\n");
 		return 1;
@@ -566,16 +591,16 @@
 		return 1;
 	}
 	if (sscanf(buf, "SF100 V:%d.%d.%d ", &fw[0], &fw[1], &fw[2]) != 3) {
-		msg_perr("Unexpected firmware version string!\n");
+		msg_perr("Unexpected firmware version string '%s'\n", buf);
 		return 1;
 	}
-	/* Only these versions were tested. */
-	if (fw[0] < 2 || fw[0] > 5) {
-		msg_perr("Unexpected firmware version %d.%d.%d!\n", fw[0],
-			 fw[1], fw[2]);
+	/* Only these major versions were tested. */
+	if (fw[0] < 2 || fw[0] > 6) {
+		msg_perr("Unexpected firmware version %d.%d.%d!\n", fw[0], fw[1], fw[2]);
 		return 1;
 	}
 	dediprog_firmwareversion = FIRMWARE_VERSION(fw[0], fw[1], fw[2]);
+
 	return 0;
 }
 
@@ -700,8 +725,8 @@
 
 static const struct spi_master spi_master_dediprog = {
 	.type		= SPI_CONTROLLER_DEDIPROG,
-	.max_data_read	= MAX_DATA_UNSPECIFIED,
-	.max_data_write	= MAX_DATA_UNSPECIFIED,
+	.max_data_read	= 16, /* 18 seems to work fine as well, but 19 times out sometimes with FW 5.15. */
+	.max_data_write	= 16,
 	.command	= dediprog_spi_send_command,
 	.multicommand	= default_spi_send_multicommand,
 	.read		= dediprog_spi_read,
@@ -711,8 +736,6 @@
 
 static int dediprog_shutdown(void *data)
 {
-	msg_pspew("%s\n", __func__);
-
 	dediprog_firmwareversion = FIRMWARE_VERSION(0, 0, 0);
 
 	/* URB 28. Command Set SPI Voltage to 0. */
@@ -730,7 +753,6 @@
 	return 0;
 }
 
-/* URB numbers refer to the first log ever captured. */
 int dediprog_init(void)
 {
 	struct usb_device *dev;
@@ -741,8 +763,6 @@
 	long target = 1;
 	int i, ret;
 
-	msg_pspew("%s\n", __func__);
-
 	spispeed = extract_programmer_param("spispeed");
 	if (spispeed) {
 		for (i = 0; spispeeds[i].name; ++i) {
@@ -861,7 +881,7 @@
 
 	/* Set all possible LEDs as soon as possible to indicate activity.
 	 * Because knowing the firmware version is required to set the LEDs correctly we need to this after
-	 * dediprog_setup() has queried the device and set dediprog_firmwareversion. */
+	 * dediprog_check_devicestring() has queried the device and set dediprog_firmwareversion. */
 	dediprog_set_leds(LED_ALL);
 
 	/* Select target/socket, frequency and VCC. */
@@ -872,9 +892,8 @@
 		return 1;
 	}
 
-	register_spi_master(&spi_master_dediprog);
-
-	dediprog_set_leds(LED_NONE);
+	if (register_spi_master(&spi_master_dediprog) || dediprog_set_leds(LED_NONE))
+		return 1;
 
 	return 0;
 }