Factor out a libhw

1 files changed, 123 insertions, 0 deletions

diff --git a/libhw/rp2040_hwspi.c b/libhw/rp2040_hwspi.c
new file mode 100644
index 0000000..b041bc9
--- /dev/null
+++ b/libhw/rp2040_hwspi.c
@@ -0,0 +1,123 @@
+/* libhw/rp2040_hwspi.c - `implements_spi` implementation for the RP2040's
+ *                        ARM Primecell SSP (PL022) (implementation file)
+ *
+ * Copyright (C) 2024  Luke T. Shumaker <lukeshu@lukeshu.com>
+ * SPDX-Licence-Identifier: AGPL-3.0-or-later
+ */
+
+#include <assert.h>
+
+#include <hardware/spi.h>  /* pico-sdk:hardware_spi */
+#include <hardware/gpio.h> /* pico-sdk:hardware_gpio */
+
+#include <libmisc/vcall.h>
+
+#include <libhw/rp2040_hwspi.h>
+
+static void rp2040_hwspi_readwritev(implements_spi *, const struct bidi_iovec *iov, int iovcnt);
+
+struct spi_vtable rp2040_hwspi_vtable = {
+	.readwritev = rp2040_hwspi_readwritev,
+};
+
+void _rp2040_hwspi_init(struct rp2040_hwspi *self,
+                        enum rp2040_hwspi_instance inst_num,
+                        enum spi_mode mode,
+                        uint baudrate_hz,
+                        uint pin_miso,
+                        uint pin_mosi,
+                        uint pin_clk,
+                        uint pin_cs) {
+	/* Be not weary: This is but 12 lines of actual code; and many
+	 * lines of comments and assert()s.  */
+	spi_inst_t *inst;
+
+	assert(self);
+	assert(baudrate_hz);
+	assert(pin_miso != pin_mosi);
+	assert(pin_miso != pin_clk);
+	assert(pin_miso != pin_cs);
+	assert(pin_mosi != pin_clk);
+	assert(pin_mosi != pin_cs);
+	assert(pin_clk != pin_cs);
+
+	/* I know we called this "hwspi", but we're actually going to
+	 * disconnect the CS pin from the PL022 SSP and manually drive
+	 * it from software.  This is because the PL022 has a maximum
+	 * of 16-bit frames, while we need to be able to do *at least*
+	 * 32-bit frames (and ideally, much larger).  By managing it
+	 * ourselves, we can just keep CS pulled low extra-long,
+	 * making the frame extra-long.  */
+
+	/* Regarding the constraints on pin assignments: see the
+	 * RP2040 datasheet, table 2, in §1.4.3 "GPIO Functions".  */
+	switch (inst_num) {
+	case RP2040_HWSPI_0:
+		inst = spi0;
+		assert(pin_miso ==  0 || pin_miso ==  4 || pin_miso == 16 || pin_miso == 20);
+		/*assert(pin_cs   ==  1 || pin_cs   ==  5 || pin_cs   == 17 || pin_cs   == 21);*/
+		assert(pin_clk  ==  2 || pin_clk  ==  6 || pin_clk  == 18 || pin_clk  == 22);
+		assert(pin_mosi ==  3 || pin_mosi ==  7 || pin_mosi == 19 || pin_mosi == 23);
+		break;
+	case RP2040_HWSPI_1:
+		inst = spi1;
+		assert(pin_miso ==  8 || pin_miso == 12 || pin_miso == 24 || pin_miso == 28);
+		/*assert(pin_cs   ==  9 || pin_cs   == 13 || pin_cs   == 25 || pin_cs   == 29);*/
+		assert(pin_clk  == 10 || pin_clk  == 14 || pin_clk  == 26);
+		assert(pin_mosi == 11 || pin_mosi == 15 || pin_mosi == 27);
+		break;
+	default:
+		assert(false);
+	}
+
+	spi_init(inst, baudrate_hz);
+	spi_set_format(inst, 8,
+	               (mode & 0b10) ? SPI_CPOL_1 : SPI_CPOL_0,
+	               (mode & 0b01) ? SPI_CPHA_1 : SPI_CPHA_0,
+	               SPI_MSB_FIRST);
+
+	/* Connect the pins to the PL022; set them each to "function
+	 * 1" (again, see the RP2040 datasheet, table 2, in §1.4.3
+	 * "GPIO Functions").
+	 *
+	 * ("GPIO_FUNC_SPI" is how the pico-sdk spells "function 1",
+	 * since on the RP2040 all of the "function 1" functions are
+	 * some part of SPI.)  */
+	gpio_set_function(pin_clk,  GPIO_FUNC_SPI);
+	gpio_set_function(pin_mosi, GPIO_FUNC_SPI);
+	gpio_set_function(pin_miso, GPIO_FUNC_SPI);
+
+	/* Initialize the CS pin for software control.  */
+	gpio_init(pin_cs);
+	gpio_set_dir(pin_cs, GPIO_OUT);
+	gpio_put(pin_cs, 1);
+
+	/* Return.  */
+	self->vtable = &rp2040_hwspi_vtable;
+	self->inst = inst;
+	self->pin_cs = pin_cs;
+}
+
+static void rp2040_hwspi_readwritev(implements_spi *_self, const struct bidi_iovec *iov, int iovcnt) {
+	struct rp2040_hwspi *self = VCALL_SELF(struct rp2040_hwspi, implements_spi, _self);
+	assert(self);
+	spi_inst_t *inst = self->inst;
+
+	assert(inst);
+	assert(iov);
+	assert(iovcnt);
+
+	gpio_put(self->pin_cs, 0);
+	/* TODO: Replace blocking reads+writes with DMA.  */
+	for (int i = 0; i < iovcnt; i++) {
+		if (iov[i].iov_write_src && iov[i].iov_read_dst)
+			spi_write_read_blocking(inst, iov[i].iov_write_src, iov[i].iov_read_dst, iov[i].iov_len);
+		else if (iov[i].iov_write_src)
+			spi_write_blocking(inst, iov[i].iov_write_src, iov[i].iov_len);
+		else if (iov[i].iov_read_dst)
+			spi_read_blocking(inst, 0, iov[i].iov_read_dst, iov[i].iov_len);
+		else
+			assert(false);
+	}
+	gpio_put(self->pin_cs, 1);
+}