ibmpc: siemens: Add inhibit after send/recv #747

SIEMENS PCD 2 Keyboard seems to require "inhibit" for a while after
sending and receiving session, for some reason.
A computer that can work with the keyboard adds "inhibit" after
communications, and this appears to be remedy for the keyboard.
https://github.com/tmk/tmk_keyboard/issues/747

converter/ibmpc_usb/config.h

@@ -45,6 +45,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 // G80-2551 terminal keyboard support
 #define G80_2551_SUPPORT
 
+// SIEMENS PCD 2 keyboard support
+#define SIEMENS_PCD_SUPPORT
+
 // Mouse Extended Report
 //#define MOUSE_EXT_REPORT
 

tmk_core/protocol/ibmpc.cpp

@@ -140,6 +140,13 @@ RETRY:
     WAIT(data_hi, 300, 7);
     WAIT(clock_hi, 300, 8);
 
+#ifdef SIEMENS_PCD_SUPPORT
+    // inhibit - https://github.com/tmk/tmk_keyboard/issues/747
+    wait_us(15);
+    clock_lo();
+    wait_us(150);
+#endif
+
     // clear buffer to get response correctly
     host_isr_clear();
 
@@ -360,6 +367,13 @@ void IBMPC::isr(void)
     }
 
 DONE:
+#ifdef SIEMENS_PCD_SUPPORT
+    // inhibit - https://github.com/tmk/tmk_keyboard/issues/747
+    clock_lo();
+    wait_us(150);
+    clock_hi();
+#endif
+
     // store data
     ringbuf_put(isr_state & 0xFF);
     if (ringbuf_is_full()) {