87 maximum frequency 375 khz

docs/src/modules/stepgen.rst

@@ -19,12 +19,6 @@ and velocity mode during operations.
     position to veloctiy, you can keep your current setup when you explicitly set te pin ``velocity-mode``
     to TRUE.
 
-.. note::
-    At this moment the timings can be set for each stepgen channel. At start up these timings are 
-    aggregated to a single timing which is applied to the whole stepgen. This means that the slowest 
-    drive will determine the maximum speed of the machine. In future release of LitexCNC this behavior
-    will be changed and timings will be applied independently.
-
 Step types
 ==========
 
@@ -63,6 +57,7 @@ The code-block belows gives an example for the configuration of ``StepGen`` for
                             "step_pin": "j9:0",
                             "dir_pin": "j9:1"
                         },
+                        "max_frequency": 400000,
                         "soft_stop": true
                     },
                 ...
@@ -89,6 +84,7 @@ The code-block belows gives an example for the configuration of ``StepGen`` for
                             "dir_pos_pin": "j9:2",
                             "dir_neg_pin": "j9:4"
                         },
+                        "max_frequency": 400000
                         "soft_stop": true
                     },
                 ...
@@ -98,6 +94,17 @@ The code-block belows gives an example for the configuration of ``StepGen`` for
         ]
         ...
 
+.. info::
+    The maximum frequency in the configuration is the guaranteed maximum frequency the
+    stepgen can reach. The actual maximum frequency depends on the clock speed of the
+    FPGA and the scaling of this clock powers with a power of 2. 
+
+    The maximum frequency should be chosen to be as close as possible to the maximum
+    frequency supported by the drive. Setting this value to a high value would lead
+    to reduction in resolution of the speed of the stepgen.
+
+    The field ``max_frequency`` is optional. When not set, it will default to 400 kHz.
+
 HAL
 ===
 
@@ -191,6 +198,11 @@ The relevant parameters which are exported to the HAL are:
 <board-name>.stepgen.<index/name>.dir-setup-time (FLOAT)
     The minimum setup time from direction to step, in nanoseconds periods. Measured from 
     change of direction to rising edge of step.
+<board-name>.stepgen.<index/name>.max_frequency (FLOAT)
+    The maximum frequency the FPGA can generate pulses. This maximum frequency is determined
+    based on the ``steplen`` and ``stepspace`` parameters and the fixed point math in the
+    FPGA (i.e. protection against rollovers). This frequency can be higher then the maximum
+    frequency requested in the JSON configuration file.
 
 Timing parameters - up/down
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^

src/litexcnc/config/modules/stepgen.py

@@ -1,4 +1,5 @@
 # Imports for creating a json-definition
+import math
 import os
 try:
     from typing import ClassVar, List, Literal, Union
@@ -128,6 +129,14 @@ class StepgenInstanceConfig(BaseModel):
         ...,
         description="The configuration of the stepper type and pin-out."
     )
+    max_frequency: bool = Field(
+        400e3,
+        description="The guaranteed maximum frequency the stepgen can generate in Hz. "
+        "The actual value can be larger then this value, as this is dependent on "
+        "the clock-frequency and scaling. Choosing a smaller value, close to the "
+        "limits of your drivers, gives a higher resolution in the velocity. Default "
+        "value is 400,000 Hz (400 kHz)."
+    )
     soft_stop: bool = Field(
         False,
         description="When False, the stepgen will directly stop when the stepgen is "
@@ -158,6 +167,13 @@ class StepgenInstanceConfig(BaseModel):
         'dir-hold-time',
     ]
 
+    def calculate_shift(self, mmio):
+        clock_frequency = mmio.clock_frequency.status.reset.value
+        shift = 0
+        while (clock_frequency / (1 << (shift+2)) > self.max_frequency):
+            shift += 1
+        return shift
+
 
 class StepgenModuleConfig(ModuleBaseModel):
     """
@@ -197,14 +213,30 @@ def add_mmio_read_registers(self, mmio):
 
     @property
     def config_size(self):
-        return 4
+        """Calculates the number DWORDS required to store the shift data
+        of the stepgen instances. The first byte is the number of instances,
+        followed by the shifts required for each instance to get the desired
+        maximum frequency.
+        """
+        return math.ceil((1 + len(self.instances)) / 4) * 4
 
     def store_config(self, mmio):
+        """Calculates the shift for each instance and stores them in the
+        MMIO. To calculate the shift, the clock-frequency is required. This
+        is taken from the MMIO register, not to break with current design
+        of this module.
+        """
         # Deferred imports to prevent importing Litex while installing the driver
         from litex.soc.interconnect.csr import CSRStatus
+        # - store the number of instances
+        config = len(self.instances) << (self.config_size * 8 - 8)
+        # - calculate and store the shift for each instance
+        clock_frequency = mmio.clock_frequency.status.reset.value
+        for index, instance in enumerate(self.instances):
+            config += instance.calculate_shift(mmio) << (self.config_size * 8 - (2 + index) * 8) 
         mmio.stepgen_config_data =  CSRStatus(
             size=self.config_size*8,
-            reset=len(self.instances),
+            reset=config,
             description=f"The config of the Stepgen module."
         )