Merge pull request #123 from riscv/fast_rbb

Add read buffer to bitbang, improving performance.

src/jtag/drivers/bitbang.c

@@ -185,10 +185,11 @@ static void bitbang_stableclocks(int num_cycles)
 	}
 }
 
-static void bitbang_scan(bool ir_scan, enum scan_type type, uint8_t *buffer, int scan_size)
+static void bitbang_scan(bool ir_scan, enum scan_type type, uint8_t *buffer,
+		unsigned scan_size)
 {
 	tap_state_t saved_end_state = tap_get_end_state();
-	int bit_cnt;
+	unsigned bit_cnt;
 
 	if (!((!ir_scan &&
 			(tap_get_state() == TAP_DRSHIFT)) ||
@@ -202,8 +203,8 @@ static void bitbang_scan(bool ir_scan, enum scan_type type, uint8_t *buffer, int
 		bitbang_end_state(saved_end_state);
 	}
 
+	size_t buffered = 0;
 	for (bit_cnt = 0; bit_cnt < scan_size; bit_cnt++) {
-		int val = 0;
 		int tms = (bit_cnt == scan_size-1) ? 1 : 0;
 		int tdi;
 		int bytec = bit_cnt/8;
@@ -219,16 +220,31 @@ static void bitbang_scan(bool ir_scan, enum scan_type type, uint8_t *buffer, int
 
 		bitbang_interface->write(0, tms, tdi);
 
-		if (type != SCAN_OUT)
-			val = bitbang_interface->read();
+		if (type != SCAN_OUT) {
+			if (bitbang_interface->buf_size) {
+				bitbang_interface->sample();
+				buffered++;
+			} else {
+				int val = bitbang_interface->read();
+				if (val)
+					buffer[bytec] |= bcval;
+				else
+					buffer[bytec] &= ~bcval;
+			}
+		}
 
 		bitbang_interface->write(1, tms, tdi);
 
-		if (type != SCAN_OUT) {
-			if (val)
-				buffer[bytec] |= bcval;
-			else
-				buffer[bytec] &= ~bcval;
+		if (type != SCAN_OUT && bitbang_interface->buf_size &&
+				(buffered == bitbang_interface->buf_size ||
+				 bit_cnt == scan_size - 1)) {
+			for (unsigned i = bit_cnt + 1 - buffered; i <= bit_cnt; i++) {
+				if (bitbang_interface->read_sample())
+					buffer[i/8] |= 1 << (i % 8);
+				else
+					buffer[i/8] &= ~(1 << (i % 8));
+			}
+			buffered = 0;
 		}
 	}
 
@@ -309,13 +325,14 @@ int bitbang_execute_queue(void)
 				bitbang_path_move(cmd->cmd.pathmove);
 				break;
 			case JTAG_SCAN:
-#ifdef _DEBUG_JTAG_IO_
-				LOG_DEBUG("%s scan end in %s",
-						(cmd->cmd.scan->ir_scan) ? "IR" : "DR",
-					tap_state_name(cmd->cmd.scan->end_state));
-#endif
 				bitbang_end_state(cmd->cmd.scan->end_state);
 				scan_size = jtag_build_buffer(cmd->cmd.scan, &buffer);
+#ifdef _DEBUG_JTAG_IO_
+				LOG_DEBUG("%s scan %d bits; end in %s",
+						(cmd->cmd.scan->ir_scan) ? "IR" : "DR",
+						scan_size,
+					tap_state_name(cmd->cmd.scan->end_state));
+#endif
 				type = jtag_scan_type(cmd->cmd.scan);
 				bitbang_scan(cmd->cmd.scan->ir_scan, type, buffer, scan_size);
 				if (jtag_read_buffer(buffer, cmd->cmd.scan) != ERROR_OK)

src/jtag/drivers/bitbang.h

@@ -27,7 +27,24 @@
 struct bitbang_interface {
 	/* low level callbacks (for bitbang)
 	 */
+
+	/* Either read() or sample()/read_sample() must be implemented. */
+
+	/* Sample TDO and return 0 or 1. */
 	int (*read)(void);
+
+	/* The sample functions allow an interface to batch a number of writes and
+	 * sample requests together. Not waiting for a value to come back can
+	 * greatly increase throughput. */
+	/* The number of TDO samples that can be buffered up before the caller has
+	 * to call read_sample. */
+	size_t buf_size;
+	/* Sample TDO and put the result in a buffer. */
+	void (*sample)(void);
+	/* Return the next unread value from the buffer. */
+	int (*read_sample)(void);
+
+	/* Set TCK, TMS, and TDI to the given values. */
 	void (*write)(int tck, int tms, int tdi);
 	void (*reset)(int trst, int srst);
 	void (*blink)(int on);

src/jtag/drivers/remote_bitbang.c

@@ -40,8 +40,58 @@
 static char *remote_bitbang_host;
 static char *remote_bitbang_port;
 
-FILE *remote_bitbang_in;
-FILE *remote_bitbang_out;
+static FILE *remote_bitbang_in;
+static FILE *remote_bitbang_out;
+static int remote_bitbang_fd;
+
+/* Circular buffer. When start == end, the buffer is empty. */
+static char remote_bitbang_buf[64];
+static unsigned remote_bitbang_start;
+static unsigned remote_bitbang_end;
+
+static int remote_bitbang_buf_full(void)
+{
+	return remote_bitbang_end ==
+		((remote_bitbang_start + sizeof(remote_bitbang_buf) - 1) %
+		 sizeof(remote_bitbang_buf));
+}
+
+/* Read any incoming data, placing it into the buffer. */
+static void remote_bitbang_fill_buf(void)
+{
+	fcntl(remote_bitbang_fd, F_SETFL, O_NONBLOCK);
+	while (!remote_bitbang_buf_full()) {
+		unsigned contiguous_available_space;
+		if (remote_bitbang_end >= remote_bitbang_start) {
+			contiguous_available_space = sizeof(remote_bitbang_buf) -
+				remote_bitbang_end;
+			if (remote_bitbang_start == 0)
+				contiguous_available_space -= 1;
+		} else {
+			contiguous_available_space = remote_bitbang_start -
+				remote_bitbang_end - 1;
+		}
+		ssize_t count = read(remote_bitbang_fd,
+				remote_bitbang_buf + remote_bitbang_end,
+				contiguous_available_space);
+		if (count > 0) {
+			remote_bitbang_end += count;
+			// TODO: check for overflow.
+			if (remote_bitbang_end == sizeof(remote_bitbang_buf)) {
+				remote_bitbang_end = 0;
+			}
+		} else if (count == 0) {
+			return;
+		} else if (count < 0) {
+			if (errno == EAGAIN) {
+				return;
+			} else {
+				REMOTE_BITBANG_RAISE_ERROR("remote_bitbang_fill_buf: %s (%d)",
+						strerror(errno), errno);
+			}
+		}
+	}
+}
 
 static void remote_bitbang_putc(int c)
 {
@@ -75,15 +125,8 @@ static int remote_bitbang_quit(void)
 	return ERROR_OK;
 }
 
-/* Get the next read response. */
-static int remote_bitbang_rread(void)
+static int char_to_int(int c)
 {
-	if (EOF == fflush(remote_bitbang_out)) {
-		remote_bitbang_quit();
-		REMOTE_BITBANG_RAISE_ERROR("fflush: %s", strerror(errno));
-	}
-
-	int c = fgetc(remote_bitbang_in);
 	switch (c) {
 		case '0':
 			return 0;
@@ -96,9 +139,42 @@ static int remote_bitbang_rread(void)
 	}
 }
 
-static int remote_bitbang_read(void)
+/* Get the next read response. */
+static int remote_bitbang_rread(void)
 {
+	if (EOF == fflush(remote_bitbang_out)) {
+		remote_bitbang_quit();
+		REMOTE_BITBANG_RAISE_ERROR("fflush: %s", strerror(errno));
+	}
+
+	/* Enable blocking access. */
+	fcntl(remote_bitbang_fd, F_SETFL, 0);
+	char c;
+	ssize_t count = read(remote_bitbang_fd, &c, 1);
+	if (count == 1) {
+		return char_to_int(c);
+	} else {
+		remote_bitbang_quit();
+		REMOTE_BITBANG_RAISE_ERROR("read: count=%d, error=%s", (int) count,
+				strerror(errno));
+	}
+}
+
+static void remote_bitbang_sample(void)
+{
+	remote_bitbang_fill_buf();
+	assert(!remote_bitbang_buf_full());
 	remote_bitbang_putc('R');
+}
+
+static int remote_bitbang_read_sample(void)
+{
+	if (remote_bitbang_start != remote_bitbang_end) {
+		int c = remote_bitbang_buf[remote_bitbang_start];
+		remote_bitbang_start = 
+			(remote_bitbang_start + 1) % sizeof(remote_bitbang_buf);
+		return char_to_int(c);
+	}
 	return remote_bitbang_rread();
 }
 
@@ -121,7 +197,9 @@ static void remote_bitbang_blink(int on)
 }
 
 static struct bitbang_interface remote_bitbang_bitbang = {
-	.read = &remote_bitbang_read,
+	.buf_size = sizeof(remote_bitbang_buf) - 1,
+	.sample = &remote_bitbang_sample,
+	.read_sample = &remote_bitbang_read_sample,
 	.write = &remote_bitbang_write,
 	.reset = &remote_bitbang_reset,
 	.blink = &remote_bitbang_blink,
@@ -199,26 +277,28 @@ static int remote_bitbang_init_unix(void)
 
 static int remote_bitbang_init(void)
 {
-	int fd;
 	bitbang_interface = &remote_bitbang_bitbang;
 
+	remote_bitbang_start = 0;
+	remote_bitbang_end = 0;
+
 	LOG_INFO("Initializing remote_bitbang driver");
 	if (remote_bitbang_port == NULL)
-		fd = remote_bitbang_init_unix();
+		remote_bitbang_fd = remote_bitbang_init_unix();
 	else
-		fd = remote_bitbang_init_tcp();
+		remote_bitbang_fd = remote_bitbang_init_tcp();
 
-	if (fd < 0)
-		return fd;
+	if (remote_bitbang_fd < 0)
+		return remote_bitbang_fd;
 
-	remote_bitbang_in = fdopen(fd, "r");
+	remote_bitbang_in = fdopen(remote_bitbang_fd, "r");
 	if (remote_bitbang_in == NULL) {
 		LOG_ERROR("fdopen: failed to open read stream");
-		close(fd);
+		close(remote_bitbang_fd);
 		return ERROR_FAIL;
 	}
 
-	remote_bitbang_out = fdopen(fd, "w");
+	remote_bitbang_out = fdopen(remote_bitbang_fd, "w");
 	if (remote_bitbang_out == NULL) {
 		LOG_ERROR("fdopen: failed to open write stream");
 		fclose(remote_bitbang_in);