leia: SPI error propagation and msg

The DAC uses the Vref selected in ADMUX.  We _must_ keep the REFS bits
stable to use the DAC as motor current reference.

Add .conf.dac_ref to initialize REFS, in case the ADC conf is missing.
Change the default ADC config to use the internal 2.5V reference for all
channels.

leia/leia.c

@@ -80,7 +80,8 @@ struct conf {
 	uint8_t       awake;          // 22
 	uint8_t       ledoff;         // 23
 	uint8_t       disable;        // 24
-	uint8_t       pad[7];         // 25
+	uint8_t       dac_ref;        // 25
+	uint8_t       pad[6];         // 26
 	uint8_t       adc_ch[16];     // 32
 };
 
@@ -109,10 +110,12 @@ struct vars {
 #define ADC_NTC1  (ADC_E | 8)
 #define ADC_NTC2  (ADC_E | 9)
 #define ADC_NTC3  (ADC_E | 10)
-#define ADC_Temp  (ADC_R | 11)
-#define ADC_Vcc   (ADC_R | 12)
+#define ADC_Temp  (ADC_E | 11)
+#define ADC_Vcc   (ADC_E | 12)
 #define ADC_BG    (ADC_E | 17)
 #define ADC_GND   (ADC_E | 18)
+#define DAC_R  ADC_R
+#define DAC_S  (DAC_R | ADC_S)
 
 __attribute__((section(".eeprom")))
 const struct conf runcon = {
@@ -127,17 +130,22 @@ const struct conf runcon = {
 	.ledoff = LEDON,
 	.awake = SLEEP,
 	.reset = RESET,
+	// The DAC uses the Vref selected here. For proper operation,
+	// all entries must use the same Vref!
 	.adc_ch = {
-		ADC_BG|ADC_SR, ADC_BG|ADC_R, ADC_GND|ADC_R,
-		ADC_Iprim|ADC_SR, ADC_Iprim|ADC_R,
-		ADC_Vcc|ADC_S, ADC_Vcc, ADC_Temp,
-		ADC_BG|ADC_S, ADC_BG, ADC_GND,
-		ADC_Iprim, ADC_NTC1, ADC_NTC2, ADC_NTC3,
+		ADC_BG|DAC_S, ADC_BG|DAC_R,
+		ADC_GND|DAC_S, ADC_GND|DAC_R,
+		ADC_Iprim|DAC_S, ADC_Iprim|DAC_R,
+		ADC_Vcc|DAC_S, ADC_Vcc|DAC_R,
+		ADC_Temp|DAC_R,
+		ADC_Iprim|DAC_R,
+		ADC_NTC1|DAC_R, ADC_NTC2|DAC_R, ADC_NTC3|DAC_R,
 	},
-	.adc_incr = 16, // one conversions per channel
+	.dac_ref = DAC_R | ADC_BG,
+	.adc_incr = 16, // one conversion per channel
 	.adc_period = TICK_NS(1000000),
 	.dac_step = 0x20,
-	.pad = "\xff\xff\xff\xff\xff\xff\xff",
+	.pad = "\xff\xff\xff\xff\xff\xff",
 };
 
 void stepper_init()
@@ -402,6 +410,7 @@ void adc_init()
 	DIDR0 = 1<<ADC3D;
 	DIDR1 = 1<<ADC8D | 1<<ADC9D | 1<<ADC10D;
 	ADCSRB = 1<<AREFEN | 2<<ADTS0;
+	ADMUX = v.conf.dac_ref;
 	ADCSRA = 1<<ADEN | 1<<ADIF | 6<<ADPS0;
 }
 
@@ -847,6 +856,8 @@ void reg88(uint8_t *v1, uint8_t *v2, unsigned char *r, const unsigned char *c)
 // ADC:          capture conversion results, advance MUX config
 // EE_READY:     write conf bytes to EEPROM
 
+unsigned char error_msg[6] = "\xff\xff\xff" "EEE";
+
 int main()
 {
 	MCUSR = 0;
@@ -863,8 +874,11 @@ int main()
 		unsigned char cmd[3];
 		unsigned char resp[3];
 		stepper_run();
-		if (spi_slave_Rx(cmd, 3)) {
-			spi_slave_Tx((const unsigned char*)"\xff\xff\xff" "EEY", 6);
+		unsigned char e = spi_slave_Rx(cmd, 3);
+		if (error_msg[5]) {
+			error_msg[4] = 'S';
+			error_msg[5] = e;
+			spi_slave_Tx(error_msg, sizeof(error_msg));
 			continue;
 		}
 		stepper_stop();
@@ -877,6 +891,11 @@ int main()
 			resp[1] = 'E';
 			resp[2] = cmd[0];
 			break;
+		case 'e':
+			resp[0] = 'e';
+			resp[1] = error_msg[4];
+			resp[2] = error_msg[5];
+			break;
 		case 'm': reg88(&v.conf.lmask, &v.conf.lval, resp, cmd); break;
 		case 'q': reg16(&v.conf.period, resp, cmd);
 			if (0) case 'l': reg16(&v.conf.slen, resp, cmd);

spi_slave.h

@@ -23,15 +23,17 @@ unsigned char spi_slave_Rx_status()
 	return SPSR & SPSR_IF && !(SPDR & 0x80);
 }
 
+#define SPI_LATE   0x80
+#define SPI_SHORT  0x40
+
 #define spi_slave_Rx spi_slave_Rx_n
 static inline
 unsigned char spi_slave_Rx_n(unsigned char d[], unsigned char n)
 {
-	d[0] = 0xff;
 	if (SPSR & SPSR_IF) {
-		SPSR;
-		SPDR;
-		return n;
+		SPDR = 0xff;
+		d[0] = SPDR;
+		return n | SPI_LATE;
 	}
 	register unsigned char b;
 	do {
@@ -45,7 +47,7 @@ unsigned char spi_slave_Rx_n(unsigned char d[], unsigned char n)
 		while (!(SPSR & SPSR_IF))
 			if (PIN_SSEL) {
 				if (s)
-					return n;
+					return n | SPI_SHORT;
 				s = n;
 			}
 		SPDR = 0xff;
@@ -73,7 +75,7 @@ unsigned char spi_slave_Rx_wdt(unsigned char d[], unsigned char n)
 		while (!(SPSR & SPSR_IF))
 			if (PIN_SSEL) {
 				if (s)
-					return n;
+					return n | SPI_SHORT;
 				s = n;
 			}
 		SPDR = 0xff;
@@ -92,7 +94,7 @@ unsigned char spi_slave_Tx_n(const unsigned char d[], unsigned char n)
 		register unsigned char b = *d++;
 		while (!(SPSR & SPSR_IF))
 			if (PIN_SSEL)
-				return n;
+				return n | SPI_SHORT;
 		SPDR = b;
 		n--;
 	}
@@ -174,7 +176,7 @@ static inline
 unsigned char spi_slave_Rx_sei(unsigned char d[], unsigned char n)
 {
 	if (!PIN_SSEL)
-		return 1;
+		return n | SPI_LATE;
 	PCIFR |= PCIF_SSEL;
 	sei();
 	n = spi_slave_Rx_n(d, n);
@@ -226,7 +228,7 @@ unsigned char spi_slave_Rx_sleep(unsigned char d[], unsigned char n)
 			cli();
 		}
 		d[0] = 0xff;
-		return n;
+		return n | SPI_LATE | SPI_SHORT;
 	}
 	SPSR;
 	SPDR;