From 32dafa1088e2f2428e9b67bf848faf2433216011 Mon Sep 17 00:00:00 2001
From: Sam Anthony <sam@samanthony.xyz>
Date: Fri, 24 Oct 2025 09:42:49 -0400
Subject: CAN echo systest

---
 fw/tests/system/can_echo_systest.c | 85 ++++++++++++++++++++++++++++++++++++++
 fw/tests/system/can_tx_systest.c   |  4 +-
 2 files changed, 88 insertions(+), 1 deletion(-)
 create mode 100644 fw/tests/system/can_echo_systest.c

(limited to 'fw/tests')

diff --git a/fw/tests/system/can_echo_systest.c b/fw/tests/system/can_echo_systest.c
new file mode 100644
index 0000000..798e45f
--- /dev/null
+++ b/fw/tests/system/can_echo_systest.c
@@ -0,0 +1,85 @@
+/* Listen for a standard DATA FRAME with ID 123h;
+ * echo it back with each byte of the DATA FIELD incremented by 1.
+ */
+
+#include <xc.h>
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#include "system.h"
+#include "types.h"
+#include "spi.h"
+#include "can.h"
+
+void
+main(void) {
+	sysInit();
+	spiInit();
+	canInit();
+
+	// Setup MCP2515 CAN controller
+	canSetBitTiming(CAN_TIMING_10K);
+	CanId id = {
+		.type=CAN_ID_STD,
+		.sid = {0xFF, 0xFF},
+	};
+	canSetMask0(&id); // set masks
+	canSetMask1(&id);
+	canSetFilter1(&id); // set unused filters
+	canSetFilter2(&id);
+	canSetFilter3(&id);
+	canSetFilter4(&id);
+	canSetFilter5(&id);
+	id.sid = (U16){0x01, 0x23}; // listen for message on filter 0
+	canSetFilter0(&id);
+	canIE(true); // enable interrupts on INT pin
+	canSetMode(CAN_MODE_NORMAL);
+	
+	// Enable interrupts
+	INTCON = 0x00; // clear flags
+	OPTION_REGbits.INTEDG = 0; // interrupt on falling edge
+	INTCONbits.INTE = 1; // enable INT pin
+	INTCONbits.PEIE = 1; // enable peripheral interrupts
+	INTCONbits.GIE = 1; // enable global interrupts
+
+	for (;;) {
+
+	}
+}
+
+// Add 1 to each data byte of a CAN frame and transmit it to the bus.
+static void
+echo(CanFrame *frame) {
+	U8 k;
+
+	for (k = 0u; k < frame->dlc; k++) {
+		frame->data[k]++;
+	}
+
+	canTx(frame);
+}
+
+void
+__interrupt() isr(void) {
+	U8 status;
+	CanFrame frame;
+
+	if (INTCONbits.INTF) {
+		status = canRxStatus();
+		switch (status & 0x7) { // check filter match
+		case 0u: // RXF0
+			canReadRxb0(&frame);
+			echo(&frame);
+			break;
+		case 1u: // RXF1
+			canReadRxb0(&frame); // clear interrupt flag
+			break;
+		default:
+			// Message in RXB1
+			canReadRxb1(&frame); // clear interrupt flag
+		}
+
+		INTCONbits.INTF = 0;
+	}
+}
diff --git a/fw/tests/system/can_tx_systest.c b/fw/tests/system/can_tx_systest.c
index b1dec17..ef1d7b0 100644
--- a/fw/tests/system/can_tx_systest.c
+++ b/fw/tests/system/can_tx_systest.c
@@ -1,3 +1,5 @@
+/* Periodically transmit a frame to the CAN bus. */
+
 #include <xc.h>
 
 #include <stdbool.h>
@@ -14,9 +16,9 @@ static const CanFrame frame = {
 		.type = CAN_ID_STD,
 		.sid = {0x01, 0x23},
 	},
+	.rtr = false,
 	.dlc = 8u,
 	.data = {0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77},
-	.rtr = false,
 };
 
 static U8 ctr = 0u; // timer
-- 
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