1 files changed, 44 insertions, 0 deletions
diff --git a/cmd/sbc_harness/hw/spi.h b/cmd/sbc_harness/hw/spi.h
new file mode 100644
index 0000000..4a160ca
--- /dev/null
+++ b/cmd/sbc_harness/hw/spi.h
@@ -0,0 +1,44 @@
+#ifndef _HW_SPI_H_
+#define _HW_SPI_H_
+
+#include <stddef.h> /* for size_t */
+
+enum spi_mode {
+	SPI_MODE_0 = 0, /* clk_polarity=0 (idle low), clk_phase=0 (sample on rise) */
+	SPI_MODE_1 = 1, /* clk_polarity=0 (idle low), clk_phase=1 (sample on fall) */
+	SPI_MODE_2 = 2, /* clk_polarity=1 (idle high), clk_phase=0 (sample on rise) */
+	SPI_MODE_3 = 3, /* clk_polarity=1 (idle high), clk_phase=1 (sample on fall) */
+};
+
+struct bidi_iovec {
+	void    *iov_read_dst;
+	void    *iov_write_src;
+	size_t   iov_len;
+};
+
+struct spi;
+
+/* This API assumes that an SPI frame is a multiple of 8-bits.
+ *
+ * It is my understanding that this is a common constraint of SPI
+ * hardware, and that the RP2040 is somewhat unusual in that it allows
+ * frames of any length 4-16 bits (we disconnect the CS pin from the
+ * PL022 SSP and manually GPIO it from the CPU in order to achieve
+ * longer frames).
+ *
+ * But, more relevantly: The W5500's protocol uses frames that are 4-N
+ * octets; so we have no need for an API that allows a
+ * non-multiple-of-8 number of bits.
+ */
+struct spi_vtable {
+	void (*readwritev)(struct spi *, const struct bidi_iovec *iov, int iovcnt)
+};
+
+struct spi {
+ 	struct spi_vtable      *vtable;
+
+	/* This is where your implementation data goes.  */
+	char                    data[0];
+};
+
+#endif /* _HW_SPI_H_ */