Add floppyio for rp2040

Tested on RP2040 Feather with a 3.5" Prodigy diskette, the whole
surface reads 100% across 3+ trials.

Author: jepler

lib/adafruit_floppy

@@ -0,0 +1,37 @@
+/*
+ * This file is part of the Micro Python project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2022 Jeff Epler for Adafruit Industries
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#pragma once
+
+// empirical-ish from RP2040 @ 125MHz for floppy_flux_readinto
+#define FLOPPYIO_SAMPLERATE (24000000)
+// empirical-ish from RP2040 @ 125MHz for floppy_mfm_readinto
+// my guess is these are slower because the more complex routine falls out of cache, but it's just
+// speculation because the loops are very similar. When looking at raw bins with a modified
+// version of adafruit_floppy, it can be seen that there are _two_ peaks for T2 and T3, rather
+// than a single one, around 36 (mostly) and 43 (rarer), compared to a single peak around 48.
+#define T2_5 (54)
+#define T3_5 (75)

ports/raspberrypi/common-hal/floppyio/__init__.h

@@ -5,6 +5,7 @@ CIRCUITPY_ALARM ?= 1
 
 CIRCUITPY_RP2PIO ?= 1
 CIRCUITPY_NEOPIXEL_WRITE ?= $(CIRCUITPY_RP2PIO)
+CIRCUITPY_FLOPPYIO ?= 1
 CIRCUITPY_FRAMEBUFFERIO ?= $(CIRCUITPY_DISPLAYIO)
 CIRCUITPY_FULL_BUILD ?= 1
 CIRCUITPY_AUDIOMP3 ?= 1

ports/raspberrypi/mpconfigport.mk

@@ -24,17 +24,19 @@
  * THE SOFTWARE.
  */
 
-#include "hal_gpio.h"
-
 #include "py/runtime.h"
 
 #include "shared-bindings/time/__init__.h"
 #include "shared-bindings/floppyio/__init__.h"
 #include "common-hal/floppyio/__init__.h"
 #include "shared-bindings/digitalio/DigitalInOut.h"
 
+#ifndef T2_5
 #define T2_5 (FLOPPYIO_SAMPLERATE * 5 / 2 / 1000000)
+#endif
+#ifndef T3_5
 #define T3_5 (FLOPPYIO_SAMPLERATE * 7 / 2 / 1000000)
+#endif
 
 #define MFM_IO_MMIO (1)
 #include "lib/adafruit_floppy/src/mfm_impl.h"