From d7e085b5868dc3386eaf96813feaa0f02ee3727f Mon Sep 17 00:00:00 2001
From: Sam Anthony <sam@samanthony.xyz>
Date: Sat, 25 Oct 2025 11:54:42 -0400
Subject: read/write CAN ID in EEPROM

---
 fw/eeprom.c                          | 53 ++++++++++++++++++++++++++++++++++++
 fw/eeprom.h                          | 10 +++++--
 fw/table.c                           |  2 ++
 fw/table.h                           | 14 ++++++----
 fw/tests/system/eeprom_can_systest.c |  2 +-
 fw/tests/system/eeprom_systest.c     |  2 ++
 6 files changed, 74 insertions(+), 9 deletions(-)

diff --git a/fw/eeprom.c b/fw/eeprom.c
index fdce167..71a53b1 100644
--- a/fw/eeprom.c
+++ b/fw/eeprom.c
@@ -2,10 +2,12 @@
 
 #include <stdbool.h>
 #include <stdint.h>
+#include <string.h>
 
 #include "system.h"
 #include "types.h"
 #include "spi.h"
+#include "can.h"
 
 #include "eeprom.h"
 
@@ -166,3 +168,54 @@ eepromRead(U16 addr, U8 *data, U8 size) {
 
 	return OK;
 }
+
+// Write a CAN ID to the EEPROM.
+// CAN IDs are stored in the lower 11 or 29 bits of a little-endian U32.
+// Bit 31 indicates standard/extended: 0=>std, 1=>ext.
+Status
+eepromWriteCanId(U16 addr, const CanId *id) {
+	U8 buf[4u];
+
+	// Copy ID to buffer
+	memset(buf, 0u, sizeof(buf));
+	switch (id->type) {
+	case CAN_ID_STD:
+		buf[0u] = id->sid.lo;
+		buf[1u] = id->sid.hi & 0x7;
+		break;
+	case CAN_ID_EXT:
+		memmove(buf, id->eid, sizeof(buf));
+		buf[3u] = (buf[3u] & 0x1F) | 0x80; // set EID flag
+		break;
+	default:
+		return FAIL; // unreachable
+	}
+
+	return eepromWrite(addr, buf, sizeof(buf));
+}
+
+// Read a CAN ID from the EEPROM.
+// CAN IDs are stored in the lower 11 or 29 bits of a little-endian U32.
+// Bit 31 indicates standard/extended: 0=>std, 1=>ext.
+Status
+eepromReadCanId(U16 addr, CanId *id) {
+	Status status;
+
+	// Read
+	status = eepromRead(addr, id->eid, sizeof(id->eid));
+	if (status != OK) {
+		return FAIL;
+	}
+
+	// Unpack
+	if (id->eid[3u] & 0x80) { // bit 31 is standard/extended flag
+		id->type = CAN_ID_EXT; // extended
+		id->eid[3u] &= 0x1F;
+	} else {
+		id->type = CAN_ID_STD; // standard
+		id->sid.lo = id->eid[0u];
+		id->sid.hi = id->eid[1u] & 0x7;
+	}
+
+	return OK;
+}
diff --git a/fw/eeprom.h b/fw/eeprom.h
index ab701d7..47f02e6 100644
--- a/fw/eeprom.h
+++ b/fw/eeprom.h
@@ -5,8 +5,10 @@
  *
  * Usage:
  *
+ * #include <stdbool>
  * #include <stdint.h>
  * #include "types.h"
+ * #include "can.h"
  * #include "eeprom.h"
  */
 
@@ -14,6 +16,10 @@
 #define EEPROM_CS_TRIS TRISCbits.TRISC5
 #define EEPROM_CS LATCbits.LATC5
 
+typedef U16 EepromAddr;
+
 void eepromInit(void);
-Status eepromWrite(U16 addr, U8 data[], U8 size);
-Status eepromRead(U16 addr, U8 data[], U8 size);
+Status eepromWrite(EepromAddr addr, U8 data[], U8 size);
+Status eepromRead(EepromAddr addr, U8 data[], U8 size);
+Status eepromWriteCanId(EepromAddr addr, const CanId *id);
+Status eepromReadCanId(EepromAddr addr, CanId *id);
diff --git a/fw/table.c b/fw/table.c
index a509082..fd16353 100644
--- a/fw/table.c
+++ b/fw/table.c
@@ -1,8 +1,10 @@
 #include <xc.h>
 
+#include <stdbool.h>
 #include <stdint.h>
 
 #include "types.h"
+#include "can.h"
 #include "eeprom.h"
 
 #include "table.h"
diff --git a/fw/table.h b/fw/table.h
index 91e981a..37d1a9d 100644
--- a/fw/table.h
+++ b/fw/table.h
@@ -1,8 +1,8 @@
 /* Table datastructure for storing calibrations in the EEPROM.
  *
  * A table has a fixed number of rows that define a key/value mapping.
- * Keys and values are each U16.
- * T: U16->U16
+ * Keys and values are each U32.
+ * T: U32->U32
  * Numbers are stored little-endian.
  *
  * Keys must be monotonically increasing.
@@ -12,21 +12,23 @@
  *
  * Usage:
  *
+ * #include <stdbool.h>
  * #include <stdint.h>
  * #include "types.h"
+ * #include "can.h"
+ * #include "eeprom.h"
  * #include "table.h"
  */
 
 enum {
-	TAB_KEY_SIZE = 2, // U16
-	TAB_VAL_SIZE = 2, // U16
+	TAB_KEY_SIZE = 4, // U32
+	TAB_VAL_SIZE = 4, // U32
 	TAB_ROWS = 32,
 	TAB_ROW_SIZE = TAB_KEY_SIZE + TAB_VAL_SIZE,
-	TAB_SIZE = TAB_ROWS * TAB_ROW_SIZE,
 };
 
 typedef struct {
-	U16 offset; // starting address
+	EepromAddr offset; // starting address
 } Table;
 
 // Set the key and value of row k.
diff --git a/fw/tests/system/eeprom_can_systest.c b/fw/tests/system/eeprom_can_systest.c
index 29c29e0..14e8f2d 100644
--- a/fw/tests/system/eeprom_can_systest.c
+++ b/fw/tests/system/eeprom_can_systest.c
@@ -14,8 +14,8 @@
 #include "system.h"
 #include "types.h"
 #include "spi.h"
-#include "eeprom.h"
 #include "can.h"
+#include "eeprom.h"
 
 static const CanId id = {
 	.type = CAN_ID_STD,
diff --git a/fw/tests/system/eeprom_systest.c b/fw/tests/system/eeprom_systest.c
index 8285e5c..5261532 100644
--- a/fw/tests/system/eeprom_systest.c
+++ b/fw/tests/system/eeprom_systest.c
@@ -1,10 +1,12 @@
 #include <xc.h>
 
+#include <stdbool.h>
 #include <stdint.h>
 
 #include "system.h"
 #include "types.h"
 #include "spi.h"
+#include "can.h"
 #include "eeprom.h"
 
 static const U16 addr = {0x00, 0x0A};
-- 
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