Use 20MHz, not 24MHz, master clock

jepler · jepler · commit 4581f25d76b4 · 2021-10-08T11:53:22.000-05:00
The clock module requires a very low jitter clock.  The esp32-s2 can do
this with a 20MHz clock but not a 24MHz one, because it is dividing an
internal clock of 80MHz to generate it.
diff --git a/README.rst b/README.rst
@@ -87,7 +87,6 @@ Usage Example
         vsync=board.CAMERA_VSYNC,
         href=board.CAMERA_HREF,
         mclk=board.CAMERA_XCLK,
-        mclk_frequency=24_000_000,
         size=adafruit_ov5640.OV5640_SIZE_QQVGA,
     )
     print("print chip id")
diff --git a/adafruit_ov5640.py b/adafruit_ov5640.py
@@ -818,7 +818,7 @@ def __init__(
         shutdown=None,
         reset=None,
         mclk=None,
-        mclk_frequency=24_000_000,
+        mclk_frequency=20_000_000,
         i2c_address=0x3C,
         size=OV5640_SIZE_QQVGA,
     ):  # pylint: disable=too-many-arguments
@@ -838,7 +838,11 @@ def __init__(
                 master clock signal, or None if the master clock signal is
                 already being generated.
             mclk_frequency (int): The frequency of the master clock to generate, \
-                ignored if mclk is None, requred if it is specified
+                ignored if mclk is None, requred if it is specified.
+                Note that the OV5640 requires a very low jitter clock,
+                so only specific (microcontroller-dependent) values may
+                work reliably.  On the ESP32-S2, a 20MHz clock can be generated
+                with sufficiently low jitter.
             i2c_address (int): The I2C address of the camera.
         """
 
diff --git a/examples/ov5640_directio_kaluga1_3_ili9341.py b/examples/ov5640_directio_kaluga1_3_ili9341.py
@@ -74,7 +74,6 @@
     vsync=board.CAMERA_VSYNC,
     href=board.CAMERA_HREF,
     mclk=board.CAMERA_XCLK,
-    mclk_frequency=24_000_000,
     size=adafruit_ov5640.OV5640_SIZE_QVGA,
 )
 
diff --git a/examples/ov5640_sdcard_kaluga_1_3.py b/examples/ov5640_sdcard_kaluga_1_3.py
@@ -46,7 +46,6 @@
     vsync=board.CAMERA_VSYNC,
     href=board.CAMERA_HREF,
     mclk=board.CAMERA_XCLK,
-    mclk_frequency=24_000_000,
     size=adafruit_ov5640.OV5640_SIZE_QSXGA,
 )
 
diff --git a/examples/ov5640_simpletest.py b/examples/ov5640_simpletest.py
@@ -38,7 +38,6 @@
     vsync=board.CAMERA_VSYNC,
     href=board.CAMERA_HREF,
     mclk=board.CAMERA_XCLK,
-    mclk_frequency=24_000_000,
     size=adafruit_ov5640.OV5640_SIZE_QQVGA,
 )
 print("print chip id")

Original file line number	Diff line number	Diff line change
`@@ -87,7 +87,6 @@ Usage Example`
`87`	`87`	`vsync=board.CAMERA_VSYNC,`
`88`	`88`	`href=board.CAMERA_HREF,`
`89`	`89`	`mclk=board.CAMERA_XCLK,`
`90`		`- mclk_frequency=24_000_000,`
`91`	`90`	`size=adafruit_ov5640.OV5640_SIZE_QQVGA,`
`92`	`91`	`)`
`93`	`92`	`print("print chip id")`
Original file line number	Diff line number	Diff line change
`@@ -74,7 +74,6 @@`
`74`	`74`	`vsync=board.CAMERA_VSYNC,`
`75`	`75`	`href=board.CAMERA_HREF,`
`76`	`76`	`mclk=board.CAMERA_XCLK,`
`77`		`- mclk_frequency=24_000_000,`
`78`	`77`	`size=adafruit_ov5640.OV5640_SIZE_QVGA,`
`79`	`78`	`)`
`80`	`79`
Original file line number	Diff line number	Diff line change
`@@ -46,7 +46,6 @@`
`46`	`46`	`vsync=board.CAMERA_VSYNC,`
`47`	`47`	`href=board.CAMERA_HREF,`
`48`	`48`	`mclk=board.CAMERA_XCLK,`
`49`		`- mclk_frequency=24_000_000,`
`50`	`49`	`size=adafruit_ov5640.OV5640_SIZE_QSXGA,`
`51`	`50`	`)`
`52`	`51`
Original file line number	Diff line number	Diff line change
`@@ -38,7 +38,6 @@`
`38`	`38`	`vsync=board.CAMERA_VSYNC,`
`39`	`39`	`href=board.CAMERA_HREF,`
`40`	`40`	`mclk=board.CAMERA_XCLK,`
`41`		`- mclk_frequency=24_000_000,`
`42`	`41`	`size=adafruit_ov5640.OV5640_SIZE_QQVGA,`
`43`	`42`	`)`
`44`	`43`	`print("print chip id")`