samd21: Add bit-banging neopixel support

To support neopixel devices on an arbitrary GPIO pin, we have to
bit-bang the protocol. DMA doesn't work because the SAMD21G DMAC
engine can't write to the PORT registers due to a missing connection
inside the SoC.

Signed-off-by: Keith Packard <keithp@keithp.com>

samd21/ao-neopixel.c

@@ -0,0 +1,100 @@
+/*
+ * Copyright © 2019 Keith Packard <keithp@keithp.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+#include <ao.h>
+#include <ao-snek.h>
+
+void
+ao_snek_neopixel_write(void *gpio, uint8_t pin, int npixel, struct snek_neopixel *pixels)
+{
+	volatile uint32_t *outtgl = &(((struct samd21_port *) gpio)->outtgl);
+	uint32_t value = ((uint32_t) 1 << pin);
+
+	while (npixel--) {
+		int32_t p = pixels->p;
+		uint8_t bit;
+		pixels++;
+
+		ao_arch_block_interrupts();
+		for (bit = 0; bit < 24; bit++) {
+			*outtgl = value;
+			ao_arch_nop();
+			ao_arch_nop();
+			ao_arch_nop();
+			ao_arch_nop();
+			ao_arch_nop();
+
+			ao_arch_nop();
+			ao_arch_nop();
+			ao_arch_nop();
+			if (p < 0) {
+				ao_arch_nop();
+				ao_arch_nop();
+				ao_arch_nop();
+				ao_arch_nop();
+				ao_arch_nop();
+
+				ao_arch_nop();
+				ao_arch_nop();
+				ao_arch_nop();
+				ao_arch_nop();
+				ao_arch_nop();
+
+				ao_arch_nop();
+				ao_arch_nop();
+				ao_arch_nop();
+				ao_arch_nop();
+				ao_arch_nop();
+
+				ao_arch_nop();
+				ao_arch_nop();
+				ao_arch_nop();
+
+				*outtgl = value;
+			} else {
+				*outtgl = value;
+				ao_arch_nop();
+				ao_arch_nop();
+				ao_arch_nop();
+				ao_arch_nop();
+				ao_arch_nop();
+
+				ao_arch_nop();
+				ao_arch_nop();
+				ao_arch_nop();
+				ao_arch_nop();
+				ao_arch_nop();
+
+				ao_arch_nop();
+				ao_arch_nop();
+				ao_arch_nop();
+
+			}
+			ao_arch_nop();
+			ao_arch_nop();
+			ao_arch_nop();
+			ao_arch_nop();
+			ao_arch_nop();
+
+			ao_arch_nop();
+
+			p <<= 1;
+		}
+		ao_arch_release_interrupts();
+	}
+}

samd21/ao-snek.h

@@ -44,4 +44,16 @@ ao_snek_running(bool running);
 #define SNEK_CODE_HOOK_START	ao_snek_running(true);
 #define SNEK_CODE_HOOK_STOP	ao_snek_running(false);
 
+struct snek_neopixel {
+	union {
+		struct {
+			uint8_t	_extra, b, r, g;
+		};
+		uint32_t	p;
+	};
+};
+
+void
+ao_snek_neopixel_write(void *port, uint8_t pin, int npixel, struct snek_neopixel *pixels);
+
 #endif /* _AO_SNEK_H_ */

samd21/snek-altos.builtin

@@ -29,4 +29,5 @@ eeprom.erase, 0
 reset, 0
 random.seed, 1
 random.randrange, 1
+neopixel, 1
 #include <ao-snek.h>

samd21/snek-samd21.defs

@@ -24,6 +24,7 @@ SNEK_SAMD21_SRC = \
 	ao-interrupt.c \
 	ao-led.c \
 	ao-timer.c \
+	ao-neopixel.c \
 	ao-usb-samd21.c \
 	ao-tcc-samd21.c \
 	ao-tc-samd21.c \