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system/cu: Optimize I/O performance with batch read/write

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Due to DMA-based transfers, the rx buffer can receive a large amount
of data at once. The previous character-by-character processing approach
was inefficient.

Modify character-by-character read to block read of the entire buffer.
This improves throughput and reduces CPU overhead, especially for high-speed
serial communication or other DMA-based transfers.

Signed-off-by: fangpeina <fangpeina@xiaomi.com>
This commit is contained in:
fangpeina 2025-07-08 13:19:45 +08:00 • committed by Xiang Xiao
parent 8cb7dd0694
commit c4da1b5b9f
1 changed files with 56 additions and 30 deletions
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86
system/cu/cu_main.c
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@ -103,16 +103,16 @@ static FAR void *cu_listener(FAR void *parameter)
for (; ; )
{
char buf[CONFIG_LINE_MAX];
int rc;
char ch;
rc = read(cu->devfd, &ch, 1);
rc = read(cu->devfd, buf, sizeof(buf));
if (rc <= 0)
{
break;
}
rc = write(STDOUT_FILENO, &ch, 1);
rc = write(STDOUT_FILENO, buf, rc);
if (rc <= 0)
{
break;
@ -289,6 +289,7 @@ int main(int argc, FAR char *argv[])
int start_of_line = 1;
int exitval = EXIT_FAILURE;
bool badarg = false;
bool escaping = false;
/* Initialize global data */
@ -436,55 +437,80 @@ int main(int argc, FAR char *argv[])
while (!cu->force_exit)
{
char ch;
char buf[CONFIG_LINE_MAX];
ssize_t nwrite = 0;
ssize_t nread;
ssize_t i;
if (read(STDIN_FILENO, &ch, 1) <= 0)
/* Read multiple characters at once (blocking) */
nread = read(STDIN_FILENO, buf, sizeof(buf));
if (nread <= 0)
{
continue;
}
if (start_of_line == 1 && ch == cu->escape)
/* Process each character */
for (i = 0; i < nread; i++)
{
/* We've seen and escape (~) character, echo it to local
* terminal and read the next char from serial
*/
char ch = buf[i];
write(STDOUT_FILENO, &ch, 1);
/* Check if we're waiting for an escape command character */
if (read(STDIN_FILENO, &ch, 1) <= 0)
if (escaping)
{
/* We got the escape character in previous read,
* now process the command character
*/
escaping = false;
if (cu_cmd(cu, ch) == 1)
{
cu->force_exit = true;
nread = i;
break;
}
}
if (start_of_line == 1 && ch == cu->escape)
{
/* Normal character */
if (i > nwrite)
{
write(cu->devfd, &buf[nwrite], i - nwrite);
}
nwrite = i + 1;
/* We've seen and escape (~) character, echo it to local
* terminal and read the next char from serial
*/
write(STDOUT_FILENO, &ch, 1);
start_of_line = 0;
escaping = true;
continue;
}
if (ch == cu->escape)
{
/* Escaping a tilde: handle like normal char */
/* Determine if we are now at the start of a new line or not */
write(cu->devfd, &ch, 1);
continue;
if (ch == '\n' || ch == '\r')
{
start_of_line = 1;
}
else
{
if (cu_cmd(cu, ch) == 1)
{
break;
}
start_of_line = 0;
}
}
/* Normal character */
write(cu->devfd, &ch, 1);
/* Determine if we are now at the start of a new line or not */
if (ch == '\n' || ch == '\r')
if (nread > nwrite)
{
start_of_line = 1;
}
else
{
start_of_line = 0;
write(cu->devfd, &buf[nwrite], nread - nwrite);
}
}