lcd_st7920: Use a longer delay at the start of each command/data

It appears the st7920 requires a longer delay when switching from
command to data mode (and vice-versa).  Slower MCUs don't show a
problem because the klipper command processing time results in a
sufficient delay.  However, some of the faster MCUs can process
klipper commands fast enough that the next st7920 transfer is sent too
fast.  Add an additional delay to account for this.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/extras/display.py

@@ -161,7 +161,9 @@ HD44780_chars = [
 # ST7920 (128x64 graphics) lcd chip
 ######################################################################
 
-ST7920_DELAY = .000020 # Spec says 72us, but faster is possible in practice
+# Spec says 72us, but faster is possible in practice
+ST7920_CMD_DELAY  = .000020
+ST7920_SYNC_DELAY = .000045
 
 class ST7920:
     char_right_arrow = '\x1a'
@@ -182,7 +184,6 @@ class ST7920:
         self.mcu = mcu
         self.oid = self.mcu.create_oid()
         self.mcu.add_config_object(self)
-        self.chip_delay = config.getfloat('chip_delay', ST7920_DELAY, minval=0.)
         self.send_data_cmd = self.send_cmds_cmd = None
         self.is_extended = False
         # framebuffers
@@ -195,9 +196,10 @@ class ST7920:
     def build_config(self):
         self.mcu.add_config_cmd(
             "config_st7920 oid=%u cs_pin=%s sclk_pin=%s sid_pin=%s"
-            " delay_ticks=%d" % (
+            " sync_delay_ticks=%d cmd_delay_ticks=%d" % (
                 self.oid, self.pins[0], self.pins[1], self.pins[2],
-                self.mcu.seconds_to_clock(self.chip_delay)))
+                self.mcu.seconds_to_clock(ST7920_SYNC_DELAY),
+                self.mcu.seconds_to_clock(ST7920_CMD_DELAY)))
         cmd_queue = self.mcu.alloc_command_queue()
         self.send_cmds_cmd = self.mcu.lookup_command(
             "st7920_send_cmds oid=%c cmds=%*s", cq=cmd_queue)