Ensure the buffer doesn't overflow.

Tested with a variety of prime buffer sizes.

Change-Id: I2b4835d46adf4c971111da88e8de4b46eb8dad41

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)) ||
@@ -202,6 +203,7 @@ 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 tms = (bit_cnt == scan_size-1) ? 1 : 0;
 		int tdi;
@@ -219,8 +221,9 @@ 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) {
-			if (bitbang_interface->sample) {
+			if (bitbang_interface->buf_size) {
 				bitbang_interface->sample();
+				buffered++;
 			} else {
 				int val = bitbang_interface->read();
 				if (val)
@@ -231,17 +234,17 @@ static void bitbang_scan(bool ir_scan, enum scan_type type, uint8_t *buffer, int
 		}
 
 		bitbang_interface->write(1, tms, tdi);
-	}
 
-	if (type != SCAN_OUT && bitbang_interface->sample) {
-		for (bit_cnt = 0; bit_cnt < scan_size; bit_cnt++) {
-			int bytec = bit_cnt/8;
-			int bcval = 1 << (bit_cnt % 8);
-			int val = bitbang_interface->read_sample();
-			if (val)
-				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[bytec] &= ~bcval;
+					buffer[i/8] &= ~(1 << (i % 8));
+			}
+			buffered = 0;
 		}
 	}
 
@@ -322,13 +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

@@ -36,6 +36,9 @@ struct bitbang_interface {
 	/* 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. */

src/jtag/drivers/remote_bitbang.c

@@ -44,18 +44,36 @@ 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 (1) {
+	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,
-				sizeof(remote_bitbang_buf) - remote_bitbang_end);
+				contiguous_available_space);
 		if (count > 0) {
 			remote_bitbang_end += count;
 			// TODO: check for overflow.
@@ -77,7 +95,6 @@ static void remote_bitbang_fill_buf(void)
 
 static void remote_bitbang_putc(int c)
 {
-	remote_bitbang_fill_buf();
 	if (EOF == fputc(c, remote_bitbang_out))
 		REMOTE_BITBANG_RAISE_ERROR("remote_bitbang_putc: %s", strerror(errno));
 }
@@ -145,6 +162,8 @@ static int remote_bitbang_rread(void)
 
 static void remote_bitbang_sample(void)
 {
+	remote_bitbang_fill_buf();
+	assert(!remote_bitbang_buf_full());
 	remote_bitbang_putc('R');
 }
 
@@ -178,6 +197,7 @@ static void remote_bitbang_blink(int on)
 }
 
 static struct bitbang_interface remote_bitbang_bitbang = {
+	.buf_size = sizeof(remote_bitbang_buf) - 1,
 	.sample = &remote_bitbang_sample,
 	.read_sample = &remote_bitbang_read_sample,
 	.write = &remote_bitbang_write,