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Diffstat (limited to 'slowbaud.rst')
| -rw-r--r-- | slowbaud.rst | 49 |
1 files changed, 38 insertions, 11 deletions
diff --git a/slowbaud.rst b/slowbaud.rst index 13e9e64..e88f890 100644 --- a/slowbaud.rst +++ b/slowbaud.rst @@ -21,9 +21,11 @@ simulate a low bitrate serial connection SYNOPSIS ======== -**slowbaud** *<bits-per-sec>* [*<file>* ...] +**slowbaud** [*<bits-per-sec>*] [*<file>* ...] -**slowbaud** *<bits-per-sec>* **-c** [*<command>* [*<arg>* ...]] +**slowbaud** [*<bits-per-sec>*] **-c** [*<command>* [*<arg>* ...]] + +**slowbaud** [*<bits-per-sec>*] **-e** *<string>* [*<string>* ...] DESCRIPTION =========== @@ -31,21 +33,40 @@ DESCRIPTION slowbaud by default acts as a filter, or like the **cat(1)** command. It reads files or its standard input, and writes the contents unmodified to standard output... but slowly, at the given bits-per-second rate. -Output is unbuffered. +Input and output are unbuffered. + +slowbaud can also act like **echo(1)** (the **-e** option), or run an +interactive command (the **-c** option). + +The *<bits-per-sec>* argument is optional. If it's not given, the +bit rate will be set from **SLOWBAUD_BPS** in the environment, or a +built-in default of 2400 if not set. + +OPTIONS +======= -With the **-c** option, it creates a pseudo-tty and runs the given command -in it (or an interactive shell, if no command is given). +**bits-per-sec** + The bit ("baud") rate to simulate. This must be the first argument. + slowbaud assumes that if the first argument is a number, it's the bit rate. + If you're trying to pass a filename that consists only of digits, give + **--** as the first argument, or use e.g. *./filename*. -The *<bits-per-sec>* argument supports a range of 1 to 500000. Timing -accuracy depends on your OS, kernel config (HZ and/or NO_HZ on Linux), -and system load. No "fancy" techniques like realtime scheduling -or hardware event timers are used. At bitrates up to 57600, on a -typical unloaded Linux system, the timing should be around 99.7% -accurate. +**-e** + Echo mode. Prints all further arguments as strings to stdout, separated + by a single space, at the given bit rate. Does not support backslash-escapes, or any of + the options of the regular **echo** command. + +**-c** + Command mode. Next argument (if present) is the command to run, any remaining arguments + become arguments to the command. With no arguments after **-c**, a shell is spawned. + This creates a pseudo-tty, so the command can be interactive. ENVIRONMENT =========== +**SLOWBAUD_BPS** + Can be used to set the bit rate, when no *<bits-per-sec>* argument is used. + **SLOWBAUD_DEBUG** Set this (to any value) in the environment to see verbose debug output on stderr, including timing accuracy stats. @@ -69,6 +90,12 @@ Of course, the child process could also exit with status 127... NOTES ===== +The bitrate has a range of 1 to 500000. Timing accuracy depends on +your OS, kernel config (HZ and/or NO_HZ on Linux), and system load. No +"fancy" techniques like realtime scheduling or hardware event timers +are used. At bitrates up to 57600, on a typical unloaded Linux system, +the timing should be at least 99.7% accurate. + We can't really insert a delay between the bits of a byte, since I/O is done with byte granularity. For calculation purposes, *<bits-per-sec>* is divided by 10 to get bytes per second. This |