Add remote bitbang write buffer.

Change 7dd323b26 reduced remote bitbang performance a lot. This change
gets most of that performance back again, by reintroducing a write
buffer.

Performance numbers collected using DebugBreakpoint test from
riscv-tests/debug against a single 64-bit spike (RISC-V simulator)
instance. (Ubuntu 20.04.2, AMD Ryzen 5 3600)
Before Windows support was added: 3.09s
After Windows support was added: 12.67s
After this change: 4.69s

Signed-off-by: Tim Newsome <tim@sifive.com>
Change-Id: I72ff4912cbbf316a30ef065e5b8f461a555f06cc
Reviewed-on: http://openocd.zylin.com/6283
Tested-by: jenkins
Reviewed-by: Jan Matyas <matyas@codasip.com>
Reviewed-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

diff --git a/src/jtag/drivers/remote_bitbang.c b/src/jtag/drivers/remote_bitbang.c
index f7b88303ba570dd853c4be45fb5eca6dcfc7e7d4..57f0c6e071a5c177f7fd42a64dea3ed5a0fb8351 100644 (file)
--- a/src/jtag/drivers/remote_bitbang.c
+++ b/src/jtag/drivers/remote_bitbang.c
@@ -36,17 +36,19 @@ static char *remote_bitbang_host;
 static char *remote_bitbang_port;
 
 static int remote_bitbang_fd;
+static uint8_t remote_bitbang_send_buf[512];
+static unsigned int remote_bitbang_send_buf_used;
 
 /* 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 char remote_bitbang_recv_buf[64];
+static unsigned int remote_bitbang_recv_buf_start;
+static unsigned int remote_bitbang_recv_buf_end;
 
-static int remote_bitbang_buf_full(void)
+static bool remote_bitbang_buf_full(void)
 {
-       return remote_bitbang_end ==
-               ((remote_bitbang_start + sizeof(remote_bitbang_buf) - 1) %
-                sizeof(remote_bitbang_buf));
+       return remote_bitbang_recv_buf_end ==
+               ((remote_bitbang_recv_buf_start + sizeof(remote_bitbang_recv_buf) - 1) %
+                sizeof(remote_bitbang_recv_buf));
 }
 
 /* Read any incoming data, placing it into the buffer. */
@@ -54,23 +56,23 @@ static int remote_bitbang_fill_buf(void)
 {
        socket_nonblock(remote_bitbang_fd);
        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)
+               unsigned int contiguous_available_space;
+               if (remote_bitbang_recv_buf_end >= remote_bitbang_recv_buf_start) {
+                       contiguous_available_space = sizeof(remote_bitbang_recv_buf) -
+                               remote_bitbang_recv_buf_end;
+                       if (remote_bitbang_recv_buf_start == 0)
                                contiguous_available_space -= 1;
                } else {
-                       contiguous_available_space = remote_bitbang_start -
-                               remote_bitbang_end - 1;
+                       contiguous_available_space = remote_bitbang_recv_buf_start -
+                               remote_bitbang_recv_buf_end - 1;
                }
                ssize_t count = read_socket(remote_bitbang_fd,
-                               remote_bitbang_buf + remote_bitbang_end,
+                               remote_bitbang_recv_buf + remote_bitbang_recv_buf_end,
                                contiguous_available_space);
                if (count > 0) {
-                       remote_bitbang_end += count;
-                       if (remote_bitbang_end == sizeof(remote_bitbang_buf))
-                               remote_bitbang_end = 0;
+                       remote_bitbang_recv_buf_end += count;
+                       if (remote_bitbang_recv_buf_end == sizeof(remote_bitbang_recv_buf))
+                               remote_bitbang_recv_buf_end = 0;
                } else if (count == 0) {
                        return ERROR_OK;
                } else if (count < 0) {
@@ -90,20 +92,43 @@ static int remote_bitbang_fill_buf(void)
        return ERROR_OK;
 }
 
-static int remote_bitbang_putc(int c)
+static int remote_bitbang_flush(void)
 {
-       char buf = c;
-       ssize_t count = write_socket(remote_bitbang_fd, &buf, sizeof(buf));
-       if (count < 0) {
-               log_socket_error("remote_bitbang_putc");
-               return ERROR_FAIL;
+       if (remote_bitbang_send_buf_used <= 0)
+               return ERROR_OK;
+
+       unsigned int offset = 0;
+       while (offset < remote_bitbang_send_buf_used) {
+               ssize_t written = write_socket(remote_bitbang_fd, remote_bitbang_send_buf + offset,
+                                                                          remote_bitbang_send_buf_used - offset);
+               if (written < 0) {
+                       log_socket_error("remote_bitbang_putc");
+                       remote_bitbang_send_buf_used = 0;
+                       return ERROR_FAIL;
+               }
+               offset += written;
        }
+       remote_bitbang_send_buf_used = 0;
+       return ERROR_OK;
+}
+
+typedef enum {
+       NO_FLUSH,
+       FLUSH_SEND_BUF
+} flush_bool_t;
+
+static int remote_bitbang_queue(int c, flush_bool_t flush)
+{
+       remote_bitbang_send_buf[remote_bitbang_send_buf_used++] = c;
+       if (flush == FLUSH_SEND_BUF ||
+                       remote_bitbang_send_buf_used >= ARRAY_SIZE(remote_bitbang_send_buf))
+               return remote_bitbang_flush();
        return ERROR_OK;
 }
 
 static int remote_bitbang_quit(void)
 {
-       if (remote_bitbang_putc('Q') == ERROR_FAIL)
+       if (remote_bitbang_queue('Q', FLUSH_SEND_BUF) == ERROR_FAIL)
                return ERROR_FAIL;
 
        if (close_socket(remote_bitbang_fd) != 0) {
@@ -135,6 +160,9 @@ static bb_value_t char_to_int(int c)
 /* Get the next read response. */
 static bb_value_t remote_bitbang_rread(void)
 {
+       if (remote_bitbang_flush() != ERROR_OK)
+               return ERROR_FAIL;
+
        /* Enable blocking access. */
        socket_block(remote_bitbang_fd);
        char c;
@@ -154,15 +182,19 @@ static int remote_bitbang_sample(void)
        if (remote_bitbang_fill_buf() != ERROR_OK)
                return ERROR_FAIL;
        assert(!remote_bitbang_buf_full());
-       return remote_bitbang_putc('R');
+       return remote_bitbang_queue('R', NO_FLUSH);
 }
 
 static bb_value_t 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);
+       if (remote_bitbang_recv_buf_start == remote_bitbang_recv_buf_end) {
+               if (remote_bitbang_fill_buf() != ERROR_OK)
+                       return ERROR_FAIL;
+       }
+       if (remote_bitbang_recv_buf_start != remote_bitbang_recv_buf_end) {
+               int c = remote_bitbang_recv_buf[remote_bitbang_recv_buf_start];
+               remote_bitbang_recv_buf_start =
+                       (remote_bitbang_recv_buf_start + 1) % sizeof(remote_bitbang_recv_buf);
                return char_to_int(c);
        }
        return remote_bitbang_rread();
@@ -171,23 +203,25 @@ static bb_value_t remote_bitbang_read_sample(void)
 static int remote_bitbang_write(int tck, int tms, int tdi)
 {
        char c = '0' + ((tck ? 0x4 : 0x0) | (tms ? 0x2 : 0x0) | (tdi ? 0x1 : 0x0));
-       return remote_bitbang_putc(c);
+       return remote_bitbang_queue(c, NO_FLUSH);
 }
 
 static int remote_bitbang_reset(int trst, int srst)
 {
        char c = 'r' + ((trst ? 0x2 : 0x0) | (srst ? 0x1 : 0x0));
-       return remote_bitbang_putc(c);
+       /* Always flush the send buffer on reset, because the reset call need not be
+        * followed by jtag_execute_queue(). */
+       return remote_bitbang_queue(c, FLUSH_SEND_BUF);
 }
 
 static int remote_bitbang_blink(int on)
 {
        char c = on ? 'B' : 'b';
-       return remote_bitbang_putc(c);
+       return remote_bitbang_queue(c, FLUSH_SEND_BUF);
 }
 
 static struct bitbang_interface remote_bitbang_bitbang = {
-       .buf_size = sizeof(remote_bitbang_buf) - 1,
+       .buf_size = sizeof(remote_bitbang_recv_buf) - 1,
        .sample = &remote_bitbang_sample,
        .read_sample = &remote_bitbang_read_sample,
        .write = &remote_bitbang_write,
@@ -268,8 +302,8 @@ static int remote_bitbang_init(void)
 {
        bitbang_interface = &remote_bitbang_bitbang;
 
-       remote_bitbang_start = 0;
-       remote_bitbang_end = 0;
+       remote_bitbang_recv_buf_start = 0;
+       remote_bitbang_recv_buf_end = 0;
 
        LOG_INFO("Initializing remote_bitbang driver");
        if (remote_bitbang_port == NULL)
@@ -326,8 +360,23 @@ static const struct command_registration remote_bitbang_command_handlers[] = {
        COMMAND_REGISTRATION_DONE,
 };
 
+static int remote_bitbang_execute_queue(void)
+{
+       /* safety: the send buffer must be empty, no leftover characters from
+        * previous transactions */
+       assert(remote_bitbang_send_buf_used == 0);
+
+       /* process the JTAG command queue */
+       int ret = bitbang_execute_queue();
+       if (ret != ERROR_OK)
+               return ret;
+
+       /* flush not-yet-sent characters, if any */
+       return remote_bitbang_flush();
+}
+
 static struct jtag_interface remote_bitbang_interface = {
-       .execute_queue = &bitbang_execute_queue,
+       .execute_queue = &remote_bitbang_execute_queue,
 };
 
 struct adapter_driver remote_bitbang_adapter_driver = {