loop_sdcard: Add loopable SD card file sections

To support continuous belt printing, add nestable repeat
loop support via an `[sdcard_loop]` module.

Supported G-Code:
  - SDCARD_LOOP_BEGIN COUNT=n  ; Loop for N times, or infinitely if N is 0
  - SDCARD_LOOP_END            ; End of loop
  - SDCARD_LOOP_DESIST         ; Complete all loops without iterating

Marlin M808 compatibility example in `config/sample-macros.cfg`:
  - M808 Ln        ; Loop for N times, or infinitely if N is 0
  - M808           ; End of loop
  - M808 K         ; Complete all loops without iterating

Added unit tests in test/klippy/sdcard_loop.test

See https://reprap.org/wiki/G-code#M808:_Set_or_Goto_Repeat_Marker

Signed-off-by: Jason S. McMullan <jason.mcmullan@gmail.com>

8 files changed, 577 insertions, 3 deletions

diff --git a/config/sample-macros.cfg b/config/sample-macros.cfg
index ea37c584..0eb049ac 100644
--- a/config/sample-macros.cfg
+++ b/config/sample-macros.cfg
@@ -176,3 +176,15 @@ gcode:
         "Humidity: %.2f%%" % (
             sensor.temperature,
             sensor.humidity))}
+
+# SDCard 'looping' (aka Marlin M808 commands) support
+#
+# Support SDCard looping
+[sdcard_loop]
+
+# 'Marlin' style M808 compatibility macro for SDCard looping
+[gcode_macro M808]
+gcode:
+    {% if params.K is not defined and params.L is defined %}SDCARD_LOOP_BEGIN COUNT={params.L|int}{% endif %}
+    {% if params.K is not defined and params.L is not defined %}SDCARD_LOOP_END{% endif %}
+    {% if params.K is defined and params.L is not defined %}SDCARD_LOOP_DESIST{% endif %}
diff --git a/docs/Config_Reference.md b/docs/Config_Reference.md
index 30c2468a..812dd7a9 100644
--- a/docs/Config_Reference.md
+++ b/docs/Config_Reference.md
@@ -1312,6 +1312,20 @@ path:
 #   be provided.
 ```
 
+## [sdcard_loop]
+
+Some printers with stage-clearing features, such as a part ejector or
+a belt printer, can find use in looping sections of the sdcard file.
+(For example, to print the same part over and over, or repeat the
+a section of a part for a chain or other repeated pattern).
+
+See the `config/sample-macros.cfg` file for a Marlin compatible M808
+G-Code macro.
+
+```
+[sdcard_loop]
+```
+
 ## [force_move]
 
 Support manually moving stepper motors for diagnostic purposes. Note,
diff --git a/docs/G-Codes.md b/docs/G-Codes.md
index 2f012bf5..cb84fa65 100644
--- a/docs/G-Codes.md
+++ b/docs/G-Codes.md
@@ -66,6 +66,13 @@ In addition, the following extended commands are availble when the
 - Load a file and start SD print: `SDCARD_PRINT_FILE FILENAME=<filename>`
 - Unload file and clear SD state: `SDCARD_RESET_FILE`
 
+When the [sdcard_loop config section](Config_Reference.md#sdcard_loop) is
+enabled, the following extended commands are available.
+- Begin a looped section in the SD print: `SDCARD_LOOP_BEGIN COUNT=<count>`
+  - A count of 0 indicates that the section should be looped indefinately.
+- End a looped section in the SD print: `SDCARD_LOOP_END`
+- Complete existing loops without further iterations: `SDCARD_LOOP_DESIST`
+
 ## G-Code arcs
 
 The following standard G-Code commands are available if a
diff --git a/klippy/extras/sdcard_loop.py b/klippy/extras/sdcard_loop.py
new file mode 100644
index 00000000..3cba979f
--- /dev/null
+++ b/klippy/extras/sdcard_loop.py
@@ -0,0 +1,73 @@
+# Sdcard file looping support
+#
+# Copyright (C) 2021  Jason S. McMullan <jason.mcmullan@gmail.com>
+#
+# This file may be distributed under the terms of the GNU GPLv3 license.
+
+import logging
+
+class SDCardLoop:
+    def __init__(self, config):
+        printer = config.get_printer()
+        self.sdcard = printer.load_object(config, "virtual_sdcard")
+        self.gcode = printer.lookup_object('gcode')
+        self.gcode.register_command(
+            "SDCARD_LOOP_BEGIN", self.cmd_SDCARD_LOOP_BEGIN,
+            desc=self.cmd_SDCARD_LOOP_BEGIN_help)
+        self.gcode.register_command(
+            "SDCARD_LOOP_END", self.cmd_SDCARD_LOOP_END,
+            desc=self.cmd_SDCARD_LOOP_END_help)
+        self.gcode.register_command(
+            "SDCARD_LOOP_DESIST", self.cmd_SDCARD_LOOP_DESIST,
+            desc=self.cmd_SDCARD_LOOP_DESIST_help)
+        self.loop_stack = []
+    cmd_SDCARD_LOOP_BEGIN_help = "Begins a looped section in the SD file."
+    def cmd_SDCARD_LOOP_BEGIN(self, gcmd):
+        count = gcmd.get_int("COUNT", minval=0)
+        if not self.loop_begin(count):
+            raise gcmd.error("Only permitted in SD file.")
+    cmd_SDCARD_LOOP_END_help = "Ends a looped section in the SD file."
+    def cmd_SDCARD_LOOP_END(self, gcmd):
+        if not self.loop_end():
+            raise gcmd.error("Only permitted in SD file.")
+    cmd_SDCARD_LOOP_DESIST_help = "Stops iterating the current loop stack."
+    def cmd_SDCARD_LOOP_DESIST(self, gcmd):
+        if not self.loop_desist():
+            raise gcmd.error("Only permitted outside of a SD file.")
+    def loop_begin(self, count):
+        if not self.sdcard.is_cmd_from_sd():
+            # Can only run inside of an SD file
+            return False
+        self.loop_stack.append((count, self.sdcard.get_file_position()))
+        return True
+    def loop_end(self):
+        if not self.sdcard.is_cmd_from_sd():
+            # Can only run inside of an SD file
+            return False
+        # If the stack is empty, no need to skip back
+        if len(self.loop_stack) == 0:
+            return True
+        # Get iteration count and return position
+        count, position = self.loop_stack.pop()
+        if count == 0: # Infinite loop
+            self.sdcard.set_file_position(position)
+            self.loop_stack.append((0, position))
+        elif count == 1: # Last repeat
+            # Nothing to do
+            pass
+        else:
+            # At the next opportunity, seek back to the start of the loop
+            self.sdcard.set_file_position(position)
+            # Decrement the count by 1, and add the position back to the stack
+            self.loop_stack.append((count - 1, position))
+        return True
+    def loop_desist(self):
+        if self.sdcard.is_cmd_from_sd():
+            # Can only run outside of an SD file
+            return False
+        logging.info("Desisting existing SD loops")
+        self.loop_stack = []
+        return True
+
+def load_config(config):
+    return SDCardLoop(config)
diff --git a/klippy/extras/virtual_sdcard.py b/klippy/extras/virtual_sdcard.py
index ccce3afe..66fc5ade 100644
--- a/klippy/extras/virtual_sdcard.py
+++ b/klippy/extras/virtual_sdcard.py
@@ -21,6 +21,7 @@ class VirtualSD:
         # Work timer
         self.reactor = printer.get_reactor()
         self.must_pause_work = self.cmd_from_sd = False
+        self.next_file_position = 0
         self.work_timer = None
         # Register commands
         self.gcode = printer.lookup_object('gcode')
@@ -124,7 +125,7 @@ class VirtualSD:
         if filename[0] == '/':
             filename = filename[1:]
         self._load_file(gcmd, filename, check_subdirs=True)
-        self.cmd_M24(gcmd)
+        self.do_resume()
     def cmd_M20(self, gcmd):
         # List SD card
         files = self.get_file_list()
@@ -191,6 +192,12 @@ class VirtualSD:
             return
         gcmd.respond_raw("SD printing byte %d/%d"
                          % (self.file_position, self.file_size))
+    def get_file_position(self):
+        return self.next_file_position
+    def set_file_position(self, pos):
+        self.next_file_position = pos
+    def is_cmd_from_sd(self):
+        return self.cmd_from_sd
     # Background work timer
     def work_handler(self, eventtime):
         logging.info("Starting SD card print (position %d)", self.file_position)
@@ -232,8 +239,11 @@ class VirtualSD:
                 continue
             # Dispatch command
             self.cmd_from_sd = True
+            line = lines.pop()
+            next_file_position = self.file_position + len(line) + 1
+            self.next_file_position = next_file_position
             try:
-                self.gcode.run_script(lines[-1])
+                self.gcode.run_script(line)
             except self.gcode.error as e:
                 self.print_stats.note_error(str(e))
                 break
@@ -241,7 +251,17 @@ class VirtualSD:
                 logging.exception("virtual_sdcard dispatch")
                 break
             self.cmd_from_sd = False
-            self.file_position += len(lines.pop()) + 1
+            self.file_position = self.next_file_position
+            # Do we need to skip around?
+            if self.next_file_position != next_file_position:
+                try:
+                    self.current_file.seek(self.file_position)
+                except:
+                    logging.exception("virtual_sdcard seek")
+                    self.work_timer = None
+                    return self.reactor.NEVER
+                lines = []
+                partial_input = ""
         logging.info("Exiting SD card print (position %d)", self.file_position)
         self.work_timer = None
         self.cmd_from_sd = False
diff --git a/test/klippy/sdcard_loop.cfg b/test/klippy/sdcard_loop.cfg
new file mode 100644
index 00000000..27844512
--- /dev/null
+++ b/test/klippy/sdcard_loop.cfg
@@ -0,0 +1,89 @@
+# Test config for sdcard_loop
+[virtual_sdcard]
+path: test/klippy/sdcard_loop
+
+[display_status]
+
+# Override to support unlimited belt size
+# (homing Z simply resets its virtual position to 0.0)
+[homing_override]
+axes: xyz
+set_position_x: 0
+set_position_y: 0
+set_position_z: 0
+gcode:
+  G92 X0 Y0 Z0
+
+
+[stepper_x]
+step_pin: ar54
+dir_pin: ar55
+enable_pin: !ar38
+step_distance: .0125
+endstop_pin: ^ar3
+position_endstop: 0
+position_max: 200
+homing_speed: 50
+
+[stepper_y]
+step_pin: ar60
+dir_pin: !ar61
+enable_pin: !ar56
+step_distance: .0125
+endstop_pin: ^ar14
+position_endstop: 0
+position_max: 200
+homing_speed: 50
+
+[stepper_z]
+step_pin: ar46
+dir_pin: ar48
+enable_pin: !ar62
+step_distance: .0025
+endstop_pin: ^ar18
+position_endstop: 0.5
+position_max: 200000000
+
+[extruder]
+step_pin: ar26
+dir_pin: ar28
+enable_pin: !ar24
+step_distance: .004242
+nozzle_diameter: 0.500
+filament_diameter: 3.500
+heater_pin: ar10
+sensor_type: EPCOS 100K B57560G104F
+sensor_pin: analog13
+control: pid
+pid_Kp: 22.2
+pid_Ki: 1.08
+pid_Kd: 114
+min_temp: 0
+max_temp: 210
+
+[heater_bed]
+heater_pin: ar8
+sensor_type: EPCOS 100K B57560G104F
+sensor_pin: analog14
+control: watermark
+min_temp: 0
+max_temp: 110
+
+[mcu]
+serial: /dev/ttyACM0
+pin_map: arduino
+
+[printer]
+kinematics: cartesian
+max_velocity: 300
+max_accel: 3000
+max_z_velocity: 5
+max_z_accel: 100
+
+[sdcard_loop]
+
+[gcode_macro M808]
+gcode:
+    {% if params.K is not defined and params.L is defined %}SDCARD_LOOP_BEGIN COUNT={params.L|int}{% endif %}
+    {% if params.K is not defined and params.L is not defined %}SDCARD_LOOP_END{% endif %}
+    {% if params.K is defined and params.L is not defined %}SDCARD_LOOP_DESIST{% endif %}
diff --git a/test/klippy/sdcard_loop.test b/test/klippy/sdcard_loop.test
new file mode 100644
index 00000000..dd9db434
--- /dev/null
+++ b/test/klippy/sdcard_loop.test
@@ -0,0 +1,9 @@
+; Virtual SD card unit tests
+
+DICTIONARY atmega2560.dict
+CONFIG sdcard_loop.cfg
+
+G28
+SDCARD_LOOP_DESIST
+; Verify long-name functions
+SDCARD_PRINT_FILE FILENAME=big.gcode
diff --git a/test/klippy/sdcard_loop/big.gcode b/test/klippy/sdcard_loop/big.gcode
new file mode 100644
index 00000000..f5e52041
--- /dev/null
+++ b/test/klippy/sdcard_loop/big.gcode
@@ -0,0 +1,350 @@
+; Large example, to test M808 looping with `partial_data`
+M808 L20
+; Looping
+G92 E0
+G91
+G1 E1 ; This is line 0
+G1 E1 ; This is line 1
+G1 E1 ; This is line 2
+G1 E1 ; This is line 3
+G1 E1 ; This is line 4
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+G1 E1 ; This is line 314
+G1 E1 ; This is line 315
+G1 E1 ; This is line 316
+G1 E1 ; This is line 317
+G1 E1 ; This is line 318
+G1 E1 ; This is line 319
+G1 E1 ; This is line 320
+G1 E1 ; This is line 321
+G1 E1 ; This is line 322
+G1 E1 ; This is line 323
+G1 E1 ; This is line 324
+G1 E1 ; This is line 325
+G1 E1 ; This is line 326
+G1 E1 ; This is line 327
+G1 E1 ; This is line 328
+G1 E1 ; This is line 329
+G1 E1 ; This one breaks
+G90
+M808
+G1 E330 ; Should pass
+SDCARD_LOOP_BEGIN COUNT=5
+; Sub-loop
+G1 X100 Y100
+G91
+M808 L3
+; Inner-loop
+G1 Z1
+M808
+G90
+SDCARD_LOOP_END
+; Done