From e7baf2e96f1cec2071cb2e1e6a4735c36611bc26 Mon Sep 17 00:00:00 2001
From: Sam Anthony <sam@samanthony.xyz>
Date: Thu, 2 Oct 2025 17:13:22 -0400
Subject: dac fw module

---
 fw/dac.c                      | 71 +++++++++++++++++++++++++++++++++++++++++++
 fw/dac.h                      | 36 ++++++++++++++++++++++
 fw/eeprom.h                   |  4 +--
 fw/spi.c                      |  2 +-
 fw/tests/system/dac_systest.c | 37 ++++++++++++++++++++++
 fw/types.c                    |  6 ++++
 fw/types.h                    |  4 +++
 7 files changed, 157 insertions(+), 3 deletions(-)
 create mode 100644 fw/dac.c
 create mode 100644 fw/dac.h
 create mode 100644 fw/tests/system/dac_systest.c

(limited to 'fw')

diff --git a/fw/dac.c b/fw/dac.c
new file mode 100644
index 0000000..0c9fb90
--- /dev/null
+++ b/fw/dac.c
@@ -0,0 +1,71 @@
+#include <xc.h>
+
+#include <stdint.h>
+
+#include "system.h"
+#include "types.h"
+#include "spi.h"
+
+#include "dac.h"
+
+// Configuration bits:
+// buffered, gain=1x, mode=active
+typedef enum {
+	CONFA = 0x70, // DAC A
+	CONFB = 0xF0, // DAC B
+} Conf;
+
+void
+dacInit(void) {
+	DAC1_CS_TRIS = OUT;
+	DAC2_CS_TRIS = OUT;
+	DAC1_CS = 1;
+	DAC2_CS = 1;
+
+	U16 level = {0u, 0u};
+	dacSet1a(level);
+	dacSet1b(level);
+	dacSet2a(level);
+	dacSet2b(level);
+}
+
+static void
+set(U8 dacNum, Conf conf, U16 level) {
+	lshiftU16(&level, 2u); // D0 at bit 2
+	level.hi = (U8)conf | (level.hi & 0x0F); // set config bits
+
+	if (dacNum == 1u) {
+		DAC1_CS = 0;
+	} else {
+		DAC2_CS = 0;
+	}
+	_delay(1);
+
+	(void)spiTx(level.hi);
+	(void)spiTx(level.lo);
+
+	if (dacNum == 1u) {
+		DAC1_CS = 1;
+	} else {
+		DAC2_CS = 1;
+	}
+}
+
+void
+dacSet1a(U16 level) {
+	set(1u, CONFA, level);
+}
+
+void
+dacSet1b(U16 level) {
+	set(1u, CONFB, level);
+}
+
+void
+dacSet2a(U16 level) {
+	set(2u, CONFA, level);
+}
+void
+dacSet2b(U16 level) {
+	set(2u, CONFB, level);
+}
diff --git a/fw/dac.h b/fw/dac.h
new file mode 100644
index 0000000..7bbf66a
--- /dev/null
+++ b/fw/dac.h
@@ -0,0 +1,36 @@
+/* Microchip MCP4912 10-bit DAC
+ *
+ * Device: PIC16F1459
+ * Compiler: XC8 v3.00
+ *
+ * Usage:
+ *
+ * #include <stdint.h>
+ * #include "types.h"
+ * #include "spi.h"
+ * #include "dac.h"
+ */
+
+// Pin mapping
+#define DAC1_CS_TRIS TRISBbits.TRISB7
+#define DAC1_CS LATBbits.LATB7
+#define DAC2_CS_TRIS TRISBbits.TRISB5
+#define DAC2_CS LATBbits.LATB5
+
+void dacInit(void);
+
+// Set DAC1 VOUTA.
+// Only the lower 10 bits are used.
+void dacSet1a(U16 level);
+
+// Set DAC1 VOUTB.
+// Only the lower 10 bits are used.
+void dacSet1b(U16 level);
+
+// Set DAC2 VOUTA.
+// Only the lower 10 bits are used.
+void dacSet2a(U16 level);
+
+// Set DAC2 VOUTB.
+// Only the lower 10 bits are used.
+void dacSet2b(U16 level);
diff --git a/fw/eeprom.h b/fw/eeprom.h
index 16d9d72..9b8652e 100644
--- a/fw/eeprom.h
+++ b/fw/eeprom.h
@@ -11,8 +11,8 @@
  */
 
 // Pin mapping
-#define EEPROM_CS_TRIS TRISAbits.TRISA5
-#define EEPROM_CS LATAbits.LATA5
+#define EEPROM_CS_TRIS TRISCbits.TRISC5
+#define EEPROM_CS LATCbits.LATC5
 
 void eepromInit(void);
 void eepromWriteEnable(void);
diff --git a/fw/spi.c b/fw/spi.c
index 9198ab1..c8abe71 100644
--- a/fw/spi.c
+++ b/fw/spi.c
@@ -15,7 +15,7 @@ spiInit(void) {
 	TRISCbits.TRISC7 = OUT; // SDO
 	TRISBbits.TRISB6 = OUT; // SCK
 
-	SSPSTAT = 0x00;
+	SSPSTAT = 0x40; // CKE=1
 	SSPCON1 = 0x22; // FOSC/64 => 750kHz SPI clock
 	junk = SSPBUF; // dummy read to clear BF
 	(void)junk;
diff --git a/fw/tests/system/dac_systest.c b/fw/tests/system/dac_systest.c
new file mode 100644
index 0000000..8653f96
--- /dev/null
+++ b/fw/tests/system/dac_systest.c
@@ -0,0 +1,37 @@
+#include <xc.h>
+
+#include <stdint.h>
+
+#include "system.h"
+#include "types.h"
+#include "spi.h"
+#include "dac.h"
+
+void
+main(void) {
+	sysInit();
+	spiInit();
+	dacInit();
+
+	dacSet1a((U16){0u, 252u}); // 1.23V
+
+	for (;;) {
+
+	}
+}
+
+void
+__interrupt() isr(void) {
+	static U8 ctr = 0u;
+	static U16 level = {0, 0};
+
+	if (TMR1IF) {
+		ctr++;
+		if (ctr == 23u) { // 1s period
+			ctr = 0u;
+			dacSet1a(level);
+			addU16(&level, 50u);
+		}
+		TMR1IF = 0;
+	}
+}
diff --git a/fw/types.c b/fw/types.c
index a6c2411..d87c891 100644
--- a/fw/types.c
+++ b/fw/types.c
@@ -11,3 +11,9 @@ addU16(U16 *a, U8 b) {
 		a->hi++;
 	}
 }
+
+void
+lshiftU16(U16 *a, U8 b) {
+	a->hi = (U8)(a->hi << b) | (a->lo >> (8u-b));
+	a->lo <<= b;
+}
diff --git a/fw/types.h b/fw/types.h
index 835491d..392c7cf 100644
--- a/fw/types.h
+++ b/fw/types.h
@@ -18,4 +18,8 @@ typedef struct {
 	U8 hi, lo;
 } U16;
 
+// *a = *a+b
 void addU16(U16 *a, U8 b);
+
+// *a = *a<<b
+void lshiftU16(U16 *a, U8 b);
-- 
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