Add ‘guile-termios’ dependency to set the speed of the inkplate TTY

There seems to be magic going on here. Once the speed has been set for the
device once the OS (at least GNU/Linux) remembers the setting and it doesn't
have to happen again after. Since I was porting from my Emacs module, I kept
running Emacs and it kept setting the speed, which meant that my tests with
Guile kept working.

After a reboot, it stopped.

This change makes sure that the speed is set. I'm not sure if the raw is
necessary, but it's in the example, and it seems to work for now, so I'll keep
it around.

configure.ac

@@ -23,7 +23,7 @@ if test "x$GUILD" = "x"; then
 fi
 
 dnl Hall auto-generated guile-module dependencies
-
+GUILE_MODULE_REQUIRED([termios])
 
 dnl Installation directories for .scm and .go files.
 guilemoduledir="${datarootdir}/guile/site/$GUILE_EFFECTIVE_VERSION"

guix.scm

@@ -23,7 +23,8 @@
       ("pkg-config" ,pkg-config)
       ("texinfo" ,texinfo)))
   (inputs `(("guile" ,guile-3.0)))
-  (propagated-inputs `())
+  (propagated-inputs
+   `(("guile-termios" ,guile-termios)))
   (synopsis "")
   (description "")
   (home-page "")

hall.scm

@@ -8,7 +8,7 @@
   (description "")
   (home-page "")
   (license gpl3+)
-  (dependencies `())
+  (dependencies `(("guile-termios" (termios) ,guile-termios)))
   (skip ())
   (files (libraries ((scheme-file "inkplate")))
          (tests ((directory "tests" ((scheme-file "inkplate")))))

inkplate.scm

@@ -1,6 +1,13 @@
 (define-module (inkplate)
   #:use-module ((ice-9 format) #:select (format))
   #:use-module ((srfi srfi-9) #:select (define-record-type))
+  #:use-module ((termios system) #:select (termios-B115200))
+  #:use-module ((termios with-exceptions)
+                #:select (make-termios-struct
+                          tc-get-attr!
+                          tc-set-attr
+                          cf-make-raw!
+                          cf-set-speed!))
 
   #:export (<inkplate>
             make-inkplate
@@ -62,7 +69,12 @@
 
 (define (open device-path)
   "Open a connection to an Inkplate on the named DEVICE-PATH."
-  (let ((port (open-file device-path "r+")))
+  (let ((port (open-file device-path "r+"))
+        (termios (make-termios-struct)))
+    (tc-get-attr! port termios)
+    (cf-make-raw! termios)
+    (cf-set-speed! termios termios-B115200)
+    (tc-set-attr port termios)
     (make-inkplate port port)))
 
 (define (close device)