refactor I2C class into Storage class. Work-in-progress.

1 files changed, 172 insertions, 0 deletions

diff --git a/src/storage.cc b/src/storage.cc
new file mode 100644
index 0000000..f755e0b
--- /dev/null
+++ b/src/storage.cc
@@ -0,0 +1,172 @@
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <util/delay.h>
+#include <stdlib.h>
+
+#include "storage.h"
+
+Storage storage;
+
+/*
+ * EEPROM data structure ("file system"):
+ *
+ * Organized as 64B-pages, all animations/texts are page-aligned.  Byte 0 ..
+ * 255 : storage metadata. Byte 0 contains the number of animations, byte 1 the
+ * byte offset of the first animation, byte 2 of the second, and so on.
+ * Byte 256+: texts/animations without additional storage metadata, aligned
+ * to 64B. So, a maximum of 256-(256/64) = 252 texts/animations can be stored,
+ * and a maximum of 255 * 64 = 16320 Bytes (almost 16 kB / 128 kbit) can be
+ * addressed.  To support larger EEPROMS, change the metadate area to Byte 2 ..
+ * 511 and use 16bit page pointers.
+ *
+ * The text/animation size is not limited by this approach.
+ *
+ * Example:
+ * Byte     0 = 3 -> we've got a total of three animations
+ * Byte     1 = 4 -> first text/animation starts at byte 64*4 = 256
+ * Byte     2 = 8 -> second starts at byte 64*8 = 512
+ * Byte     3 = 9 -> third starts at 64*9 * 576
+ * Byte     4 = whatever
+ *            .
+ *            .
+ *            .
+ * Byte 256ff = first text/animation. Has a header encoding its length in bytes.
+ * Byte 512ff = second
+ * Byte 576ff = third
+ *            .
+ *            .
+ *            .
+ */
+
+void Storage::enable()
+{
+	/*
+	 * Set I2C clock frequency to 100kHz.
+	 * freq = F_CPU / (16 + (2 * TWBR * TWPS) )
+	 * let TWPS = "00" = 1
+	 * -> TWBR = (F_CPU / 100000) - 16 / 2
+	 */
+	TWSR = 0; // the lower two bits control TWPS
+	TWBR = ((F_CPU / 100000UL) - 16) / 2;
+}
+
+
+/*
+ * Send an I2C (re)start condition and the EEPROM address in read mode. Returns
+ * after it has been transmitted successfully.
+ */
+void Storage::i2c_start_read()
+{
+	TWCR = _BV(TWINT) | _BV(TWSTA) | _BV(TWEN);
+	while (!(TWCR & _BV(TWINT)));
+
+	// Note: The R byte ("... | 1") causes the TWI momodule to switch to
+	// Master Receive mode
+	TWDR = (I2C_EEPROM_ADDR << 1) | 1;
+	TWCR = _BV(TWINT) | _BV(TWEN);
+	while (!(TWCR & _BV(TWINT)));
+}
+
+/*
+ * Send an I2C (re)start condition and the EEPROM address in write mode.
+ * Returns after it has been transmitted successfully.
+ */
+void Storage::i2c_start_write()
+{
+	TWCR = _BV(TWINT) | _BV(TWSTA) | _BV(TWEN);
+	while (!(TWCR & _BV(TWINT)));
+
+	TWDR = (I2C_EEPROM_ADDR << 1) | 0;
+	TWCR = _BV(TWINT) | _BV(TWEN);
+	while (!(TWCR & _BV(TWINT)));
+}
+
+/*
+ * Send an I2C stop condition.
+ */
+void Storage::i2c_stop()
+{
+	TWCR = _BV(TWINT) | _BV(TWSTO) | _BV(TWEN);
+}
+
+/*
+ * Sends len bytes to the EEPROM. Note that this method does NOT
+ * send I2C start or stop conditions.
+ */
+// TODO Everything[tm] (error handling and generic code)
+int8_t Storage::i2c_send(uint8_t len, uint8_t *data)
+{
+	uint8_t pos = 0;
+
+	for (pos = 0; pos < len; pos++) {
+		TWDR = data[pos];
+		TWCR = _BV(TWINT) | _BV(TWEN);
+		while (!(TWCR & _BV(TWINT)));
+	}
+
+	return pos + 1;
+}
+
+/*
+ * Receives len bytes from the EEPROM into data. Note that this method does
+ * NOT send I2C start or stop conditions.
+ */
+// TODO dito
+int8_t Storage::i2c_receive(uint8_t len, uint8_t *data)
+{
+	uint8_t pos = 0;
+
+	for (pos = 0; pos < len; pos++) {
+		if (pos == len-1) {
+			// Don't ACK the last byte
+			TWCR = _BV(TWINT) | _BV(TWEN);
+		} else {
+			// Automatically send ACK
+			TWCR = _BV(TWINT) | _BV(TWEN) | _BV(TWEA);
+		}
+		while (!(TWCR & _BV(TWINT)));
+		data[pos] = TWDR;
+	}
+
+	return pos + 1;
+}
+
+/*
+ * Writes len bytes of data into the EEPROM, starting at byte number pos.
+ * Does not check for page boundaries yet.
+ * Includes a complete I2C transaction.
+ */
+int8_t Storage::i2c_write(uint16_t pos, uint8_t len, uint8_t *data)
+{
+	uint8_t addr_buf[2];
+
+	addr_buf[0] = pos >> 8;
+	addr_buf[1] = pos & 0xff;
+
+	i2c_start_write();
+	i2c_send(2, addr_buf);
+	i2c_send(len, data);
+	i2c_stop();
+
+	return 0; // TODO proper return code to indicate write errors
+}
+
+/*
+ * Reads len bytes of data from the EEPROM, starting at byte number pos.
+ * Does not check for page boundaries yet.
+ * Includes a complete I2C transaction.
+ */
+int8_t Storage::i2c_read(uint16_t pos, uint8_t len, uint8_t *data)
+{
+	uint8_t addr_buf[2];
+	addr_buf[0] = pos >> 8;
+	addr_buf[1] = pos & 0xff;
+
+	i2c_start_write();
+	i2c_send(2, addr_buf);
+	i2c_start_read();
+	i2c_receive(len, data);
+	i2c_stop();
+
+	return 0; // TODO proper return code to indicate read/write errors
+}