SD card: establish spi.c/.h and sd.c/.h and get SPI running.

For now this is just a nice demonstration on how to send bytes
over SPI. Add SD_CARD_SELECT_PIN to your configuration board
file manually to see data signals on MOSI dancing on the scope.

The TODO's about SS in arduino*.h were wrong, SS does have a
chip-specific special meaning (used in SPI multi-master or SPI
slave mode). Still, a #define MAX6675_SELECT_PIN is missing.

Squashed in this commit from the SPI development topic branch to
get this first step working:

Author: jbernardis <jeff.bernardis@gmail.com>
2015-02-04 22:35:07
mendel.c: disable SPI in power management only when not needed.

If we want to talk to a SD card connected to SPI, we need SPI
powered, of course.

From Traumflug: nice catch, Jeff!

arduino_1280.h

@@ -6,10 +6,6 @@
 #define	SCK					DIO52
 #define	MISO				DIO50
 #define	MOSI				DIO51
-// TODO: This depends on the board, so this definition is misplaced here,
-//       should be more appropriately named and go to config.h. It's used in
-//       temp.c and simulator.h and defines the Chip Select pin for an eventual
-//       MAX6675 temperature sensor.
 #define	SS					DIO53
 
 // TWI (I2C)

arduino_168_328p.h

@@ -6,10 +6,6 @@
 #define	SCK					DIO13
 #define	MISO				DIO12
 #define	MOSI				DIO11
-// TODO: This depends on the board, so this definition is misplaced here,
-//       should be more appropriately named and go to config.h. It's used in
-//       temp.c and simulator.h and defines the Chip Select pin for an eventual
-//       MAX6675 temperature sensor.
 #define	SS					DIO10
 
 // TWI (I2C)

arduino_32U4.h

@@ -30,10 +30,6 @@
 #define SCK          DIO1
 #define MISO         DIO3
 #define MOSI         DIO2
-// TODO: This depends on the board, so this definition is misplaced here,
-//       should be more appropriately named and go to config.h. It's used in
-//       temp.c and simulator.h and defines the Chip Select pin for an eventual
-//       MAX6675 temperature sensor.
 #define SS           DIO0
 
 // TWI (I2C)

arduino_644.h

@@ -11,10 +11,6 @@
 #define	SCK					DIO7
 #define	MISO				DIO6
 #define	MOSI				DIO5
-// TODO: This depends on the board, so this definition is misplaced here,
-//       should be more appropriately named and go to config.h. It's used in
-//       temp.c and simulator.h and defines the Chip Select pin for an eventual
-//       MAX6675 temperature sensor.
 #define	SS					DIO4
 
 // TWI (I2C)

arduino_usb1286.h

@@ -11,10 +11,6 @@
 #define SCK            DIO9
 #define MISO           DIO11
 #define MOSI           DIO10
-// TODO: This depends on the board, so this definition is misplaced here,
-//       should be more appropriately named and go to config.h. It's used in
-//       temp.c and simulator.h and defines the Chip Select pin for an eventual
-//       MAX6675 temperature sensor.
 #define SS             DIO8
 
 

arduino_usb1287.h

@@ -2,10 +2,6 @@
 #define	SCK					DIO9
 #define	MISO				DIO11
 #define	MOSI				DIO10
-// TODO: This depends on the board, so this definition is misplaced here,
-//       should be more appropriately named and go to config.h. It's used in
-//       temp.c and simulator.h and defines the Chip Select pin for an eventual
-//       MAX6675 temperature sensor.
 #define	SS					DIO8
 
 

mendel.c

@@ -49,6 +49,8 @@
 #include	"clock.h"
 #include	"intercom.h"
 #include "simulator.h"
+#include "spi.h"
+#include "sd.h"
 
 #ifdef SIMINFO
   #include "../simulavr/src/simulavr_info.h"
@@ -66,9 +68,15 @@
 void io_init(void) {
 	// disable modules we don't use
 	#ifdef PRR
-		PRR = MASK(PRTWI) | MASK(PRADC) | MASK(PRSPI);
+    PRR = MASK(PRTWI) | MASK(PRADC);
+    #if ! defined TEMP_MAX6675 && ! defined SD
+      PRR |= MASK(PRSPI);
+    #endif
 	#elif defined PRR0
-		PRR0 = MASK(PRTWI) | MASK(PRADC) | MASK(PRSPI);
+    PRR0 = MASK(PRTWI) | MASK(PRADC);
+    #if ! defined TEMP_MAX6675 && ! defined SD
+      PRR0 |= MASK(PRSPI);
+    #endif
 		#if defined(PRUSART3)
 			// don't use USART2 or USART3- leave USART1 for GEN3 and derivatives
 			PRR1 |= MASK(PRUSART3) | MASK(PRUSART2);
@@ -179,20 +187,18 @@ void io_init(void) {
 		power_off();
 	#endif
 
-	#ifdef	TEMP_MAX6675
-		// setup SPI
-		WRITE(SCK, 0);				SET_OUTPUT(SCK);
-		WRITE(MOSI, 1);				SET_OUTPUT(MOSI);
-		WRITE(MISO, 1);				SET_INPUT(MISO);
-	#endif
-
   #ifdef DEBUG_LED_PIN 
     WRITE(DEBUG_LED_PIN, 0);
     SET_OUTPUT(DEBUG_LED_PIN);
   #endif
 }
 
-/// Startup code, run when we come out of reset
+/** Initialise all the subsystems.
+
+  Note that order of appearance is critical here. For example, running
+  spi_init() before io_init() makes SPI fail (for reasons not exactly
+  investigated).
+*/
 void init(void) {
 	// set up watchdog
 	wd_init();
@@ -206,6 +212,10 @@ void init(void) {
 	// set up inputs and outputs
 	io_init();
 
+  #if defined TEMP_MAX6675 || defined SD
+    spi_init();
+  #endif
+
 	// set up timers
 	timer_init();
 
@@ -222,6 +232,10 @@ void init(void) {
 	// set up temperature inputs
 	temp_init();
 
+  #ifdef SD
+    sd_init();
+  #endif
+
 	// enable interrupts
 	sei();
 
@@ -249,6 +263,23 @@ int main (void)
 #endif
 	init();
 
+  #ifdef SD
+    // This demonstrates SPI. Gives a nice dance on the scope.
+    // Will go away as soon as we can do something useful with the SD card.
+    #include "delay.h"
+    uint8_t c = 0;
+    while (1) {
+      // Trigger signal for the scope.
+      WRITE(STEPPER_ENABLE_PIN, 0);
+      delay_us(10);
+      WRITE(STEPPER_ENABLE_PIN, 1);
+
+      spi_rw(c);
+      c++;
+      delay_ms(50);
+    }
+  #endif
+
 	// main loop
 	for (;;)
 	{

sd.c

@@ -0,0 +1,15 @@
+
+/** \file Coordinating reading and writing of SD cards.
+*/
+
+#include "sd.h"
+
+#ifdef SD
+
+
+void sd_init(void) {
+  WRITE(SD_CARD_SELECT_PIN, 1);
+  SET_OUTPUT(SD_CARD_SELECT_PIN);
+}
+
+#endif /* SD */

sd.h

@@ -0,0 +1,17 @@
+
+/** \file Coordinating reading and writing of SD cards.
+*/
+
+#ifndef _SD_H
+#define _SD_H
+
+#include "config_wrapper.h"
+
+#ifdef SD_CARD_SELECT_PIN
+#define SD
+
+void sd_init(void);
+
+#endif /* SD_CARD_SELECT_PIN */
+
+#endif /* _SD_H */

spi.c

@@ -0,0 +1,45 @@
+
+/** \file
+  \brief SPI subsystem
+
+  This is much simpler than Teacup's serial subsystem. No ring buffers, no
+  "write string" functions. Usually using SPI directly is faster than fiddling
+  with buffers. For example, reading or writing a byte can be done in as few
+  as 20 clock cycles.
+
+  Other than serial, SPI has to deal with multiple devices. Device selection
+  happens before reading and writing, data exchange its self is the same for
+  each device, then.
+*/
+#include "spi.h"
+
+#include "arduino.h"
+
+
+/** Initialise serial subsystem.
+
+  Code copied from ATmega164/324/644/1284 data sheet, section 18.2, page 160,
+  or moved here from mendel.c.
+*/
+void spi_init() {
+
+  // Set SCK (clock) and MOSI line to output, ie. set USART in master mode.
+  SET_OUTPUT(SCK);
+  SET_OUTPUT(MOSI);
+  SET_INPUT(MISO);
+  // SS must be set as output to disconnect it from the SPI subsystem.
+  // Too bad if something else tries to use this pin as digital input.
+  // See ATmega164/324/644/1284 data sheet, section 18.3.2, page 162.
+  // Not written there: this must apparently be done before setting the SPRC
+  // register, else future R/W-operations may hang.
+  SET_OUTPUT(SS);
+
+  #ifdef SPI_2X
+    SPSR = 0x01;
+  #else
+    SPSR = 0x00;
+  #endif
+
+  // This sets the whole SPRC register.
+  spi_speed_100_400();
+}

spi.h

@@ -0,0 +1,102 @@
+#ifndef _SPI_H
+#define _SPI_H
+
+#include "config_wrapper.h"
+#include "arduino.h"
+
+// Uncomment this to double SPI frequency from (F_CPU / 4) to (F_CPU / 2).
+//#define SPI_2X
+
+
+/** Initialise SPI subsystem.
+*/
+void spi_init(void);
+
+/** SPI device selection.
+
+  Because out famous WRITE() macro works with constant pins, only, we define
+  a (de)select function for each of them. In case you add another SPI device,
+  you also have to define a pair of these functions.
+*/
+#ifdef SD
+static void spi_select_sd(void) __attribute__ ((always_inline));
+inline void spi_select_sd(void) {
+  WRITE(SD_CARD_SELECT_PIN, 0);
+}
+
+static void spi_deselect_sd(void) __attribute__ ((always_inline));
+inline void spi_deselect_sd(void) {
+  WRITE(SD_CARD_SELECT_PIN, 1);
+}
+#endif /* SD */
+
+#ifdef TEMP_MAX6675
+// Note: the pin choosen with DEFINE_TEMP_SENSOR() in the board configuration
+//       should be used here. Currently it's a requirement that this device's
+//       Chip Select pin is actually SS, while any other pin would work just
+//       as fine.
+static void spi_select_max6675(void) __attribute__ ((always_inline));
+inline void spi_select_max6675(void) {
+  WRITE(SS, 0);
+}
+
+static void spi_deselect_max6675(void) __attribute__ ((always_inline));
+inline void spi_deselect_max6675(void) {
+  WRITE(SS, 1);
+}
+#endif /* TEMP_MAX6675 */
+
+/** Set SPI clock speed to something between 100 and 400 kHz.
+
+  This is needed for initialising SD cards. We set the whole SPCR register
+  in one step, because this is faster than and'ing in bits.
+
+  About dividers. We have:
+  SPCR = 0x50; // normal mode: (F_CPU / 4), 2x mode: (F_CPU / 2)
+  SPCR = 0x51; // normal mode: (F_CPU / 16), 2x mode: (F_CPU / 8)
+  SPCR = 0x52; // normal mode: (F_CPU / 64), 2x mode: (F_CPU / 32)
+  SPCR = 0x53; // normal mode: (F_CPU / 128), 2x mode: (F_CPU / 64)
+
+  For now we always choose the /128 divider, because it fits nicely in all
+  expected situations:
+    F_CPU                    16 MHz    20 MHz
+    SPI clock normal mode   125 kHz   156 kHz
+    SPI clock 2x mode       250 kHz   312 kHz
+
+  About the other bits:
+  0x50 = (1 << SPE) | (1 << MSTR);
+  This is Master SPI mode, SPI enabled, interrupts disabled, polarity mode 0
+  (right for SD cards).
+  See ATmega164/324/644/1284 data sheet, section 18.5.1, page 164.
+*/
+static void spi_speed_100_400(void) __attribute__ ((always_inline));
+inline void spi_speed_100_400(void) {
+  SPCR = 0x53;
+}
+
+/** Set SPI clock speed to maximum.
+*/
+static void spi_speed_max(void) __attribute__ ((always_inline));
+inline void spi_speed_max(void) {
+  SPCR = 0x50; // See list at spi_speed_100_400().
+}
+
+/** Exchange a byte over SPI.
+
+  Yes, SPI is that simple and you can always only swap bytes. To retrieve
+  a byte, simply send a dummy value, like: mybyte = spi_rw(0);
+
+  As we operate in master mode, we don't have to fear to hang due to
+  communications errors (e.g. missing a clock beat).
+
+  Note: insisting on inlinig (attribute always_inline) costs about 80 bytes
+        with the current SD card code.
+*/
+static uint8_t spi_rw(uint8_t) __attribute__ ((always_inline));
+inline uint8_t spi_rw(uint8_t byte) {
+  SPDR = byte;
+  loop_until_bit_is_set(SPSR, SPIF);
+  return SPDR;
+}
+
+#endif /* _SPI_H */

temp.c

@@ -27,6 +27,7 @@
 #endif
 
 #ifdef	TEMP_MAX6675
+  #include "spi.h"
 #endif
 
 #ifdef	TEMP_THERMISTOR
@@ -83,8 +84,9 @@ void temp_init() {
 		switch(temp_sensors[i].temp_type) {
       #ifdef TEMP_MAX6675
         case TT_MAX6675:
-          WRITE(SS, 1); // Turn sensor off.
+          // Note that MAX6675's Chip Select pin is currently hardcoded to SS.
-          SET_OUTPUT(SS);
+          // This isn't neccessary. See also spi.h.
+          spi_deselect_max6675();
           // Intentionally no break, we might have more than one sensor type.
       #endif
 
@@ -132,33 +134,18 @@ void temp_sensor_tick() {
 			switch(temp_sensors[i].temp_type) {
 				#ifdef	TEMP_MAX6675
 				case TT_MAX6675:
-					#ifdef	PRR
+          // Note: value reading in this section was rewritten without
-						PRR &= ~MASK(PRSPI);
+          //       testing when spi.c/.h was introduced. --Traumflug
-					#elif defined PRR0
+          spi_select_max6675();
-						PRR0 &= ~MASK(PRSPI);
-					#endif
-
-					SPCR = MASK(MSTR) | MASK(SPE) | MASK(SPR0);
-
-					// enable TT_MAX6675
-					WRITE(SS, 0);
-
 					// No delay required, see
 					// https://github.com/triffid/Teacup_Firmware/issues/22
 
 					// read MSB
-					SPDR = 0;
+          temp = spi_rw(0) << 8;
-					for (;(SPSR & MASK(SPIF)) == 0;);
-					temp = SPDR;
-					temp <<= 8;
-
 					// read LSB
-					SPDR = 0;
+          temp |= spi_rw(0);
-					for (;(SPSR & MASK(SPIF)) == 0;);
-					temp |= SPDR;
 
-					// disable TT_MAX6675
+          spi_deselect_max6675();
-					WRITE(SS, 1);
 
 					temp_sensors_runtime[i].temp_flags = 0;
 					if ((temp & 0x8002) == 0) {