Implement USI peripheral slave statemachine
- Implement a TWI slave using the USI peripheral found in AVR tiny MCUs - using attiny85 as target (has no bootloader section!) - USI peripheral in general needs clock stretching support from the master since the whole statemachine is software based. For now the actual writing to flash/eeprom is also done during clock stretching (like original twiboot implementation). This might be changed later. - ACK/NAK handling is different: For TWI peripheral the ACK/NAK of the *next* byte has to be returned by TWI_data_write(). For USI peripheral the ACK/NAK of the *current* byte needs to be returned. For now the TWI version remains in the code and might be changed later.
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16
Makefile
16
Makefile
@ -8,7 +8,7 @@ TARGET = twiboot
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SOURCE = $(wildcard *.c)
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# select MCU
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MCU = atmega88
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MCU = attiny85
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AVRDUDE_PROG := -c avr910 -b 115200 -P /dev/ttyUSB0
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#AVRDUDE_PROG := -c dragon_isp -P usb
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@ -58,10 +58,22 @@ AVRDUDE_FUSES=lfuse:w:0xc2:m hfuse:w:0xdc:m efuse:w:0xfd:m
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BOOTLOADER_START=0x7C00
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endif
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ifeq ($(MCU), attiny85)
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# attiny85:
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# Fuse L: 0xe2 (8Mhz internal RC-Osz.)
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# Fuse H: 0xdd (2.7V BOD)
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# Fuse E: 0xfe (self programming enable)
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AVRDUDE_MCU=t85
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AVRDUDE_FUSES=lfuse:w:0xe2:m hfuse:w:0xdd:m efuse:w:0xfe:m
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BOOTLOADER_START=0x1C00
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CFLAGS_TARGET=-DUSE_CLOCKSTRETCH=1
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endif
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# ---------------------------------------------------------------------------
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CFLAGS = -pipe -g -Os -mmcu=$(MCU) -Wall -fdata-sections -ffunction-sections
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CFLAGS += -Wa,-adhlns=$(*F).lst -DBOOTLOADER_START=$(BOOTLOADER_START)
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CFLAGS += -Wa,-adhlns=$(*F).lst -DBOOTLOADER_START=$(BOOTLOADER_START) $(CFLAGS_TARGET)
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LDFLAGS = -Wl,-Map,$(@:.elf=.map),--cref,--relax,--gc-sections,--section-start=.text=$(BOOTLOADER_START)
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LDFLAGS += -nostartfiles
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201
main.c
201
main.c
@ -59,6 +59,33 @@
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#define LED_OFF()
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#endif /* LED_SUPPORT */
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#if !defined(TWCR) && defined(USICR)
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#define USI_PIN_INIT() { PORTB |= ((1<<PORTB0) | (1<<PORTB2)); \
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DDRB |= (1<<PORTB2); \
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}
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#define USI_PIN_SDA_INPUT() DDRB &= ~(1<<PORTB0)
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#define USI_PIN_SDA_OUTPUT() DDRB |= (1<<PORTB0)
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#define USI_PIN_SCL() (PINB & (1<<PINB2))
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#if (USE_CLOCKSTRETCH == 0)
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#error "USI peripheral requires enabled USE_CLOCKSTRETCH"
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#endif
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#define USI_STATE_MASK 0x0F
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#define USI_STATE_IDLE 0x00 /* wait for Start Condition */
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#define USI_STATE_SLA 0x01 /* wait for Slave Address */
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#define USI_STATE_SLAW_ACK 0x02 /* ACK Slave Address + Write (Master writes) */
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#define USI_STATE_SLAR_ACK 0x03 /* ACK Slave Address + Read (Master reads) */
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#define USI_STATE_NAK 0x04 /* send NAK */
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#define USI_STATE_DATW 0x05 /* receive Data */
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#define USI_STATE_DATW_ACK 0x06 /* transmit ACK for received Data */
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#define USI_STATE_DATR 0x07 /* transmit Data */
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#define USI_STATE_DATR_ACK 0x08 /* receive ACK for transmitted Data */
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#define USI_WAIT_FOR_ACK 0x10 /* wait for ACK bit (2 SCL clock edges) */
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#define USI_ENABLE_SDA_OUTPUT 0x20 /* SDA is output (slave transmitting) */
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#define USI_ENABLE_SCL_HOLD 0x40 /* Hold SCL low after clock overflow */
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#endif /* !defined(TWCR) && defined(USICR) */
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/* SLA+R */
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#define CMD_WAIT 0x00
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#define CMD_READ_VERSION 0x01
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@ -163,7 +190,11 @@ static void write_flash_page(void)
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boot_page_write(pagestart);
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boot_spm_busy_wait();
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#if defined (ASRE) || defined (RWWSRE)
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/* only required for bootloader section */
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boot_rww_enable();
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#endif
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}
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} /* write_flash_page */
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@ -386,6 +417,7 @@ static uint8_t TWI_data_read(uint8_t bcnt)
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} /* TWI_data_read */
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#if defined (TWCR)
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/* *************************************************************************
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* TWI_vect
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* ************************************************************************* */
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@ -472,6 +504,156 @@ static void TWI_vect(void)
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TWCR = (1<<TWINT) | control;
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} /* TWI_vect */
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#endif /* defined (TWCR) */
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#if defined (USICR)
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/* *************************************************************************
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* usi_statemachine
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* ************************************************************************* */
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static void usi_statemachine(uint8_t usisr)
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{
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static uint8_t usi_state;
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static uint8_t bcnt;
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uint8_t data = USIDR;
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uint8_t state = usi_state & USI_STATE_MASK;
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/* Start Condition detected */
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if (usisr & (1<<USISIF))
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{
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/* wait until SCL goes low */
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while (USI_PIN_SCL());
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usi_state = USI_STATE_SLA | USI_ENABLE_SCL_HOLD;
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state = USI_STATE_IDLE;
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}
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/* Stop Condition detected */
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if (usisr & (1<<USIPF))
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{
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LED_RT_OFF();
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usi_state = USI_STATE_IDLE;
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state = USI_STATE_IDLE;
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}
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if (state == USI_STATE_IDLE)
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{
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/* do nothing */
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}
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/* Slave Address received => prepare ACK/NAK */
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else if (state == USI_STATE_SLA)
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{
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bcnt = 0;
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/* SLA+W received -> send ACK */
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if (data == ((TWI_ADDRESS<<1) | 0x00))
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{
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LED_RT_ON();
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usi_state = USI_STATE_SLAW_ACK | USI_WAIT_FOR_ACK | USI_ENABLE_SDA_OUTPUT | USI_ENABLE_SCL_HOLD;
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USIDR = 0x00;
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}
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/* SLA+R received -> send ACK */
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else if (data == ((TWI_ADDRESS<<1) | 0x01))
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{
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LED_RT_ON();
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usi_state = USI_STATE_SLAR_ACK | USI_WAIT_FOR_ACK | USI_ENABLE_SDA_OUTPUT | USI_ENABLE_SCL_HOLD;
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USIDR = 0x00;
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}
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/* not addressed -> send NAK */
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else
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{
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usi_state = USI_STATE_NAK | USI_WAIT_FOR_ACK | USI_ENABLE_SDA_OUTPUT | USI_ENABLE_SCL_HOLD;
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USIDR = 0x80;
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}
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}
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/* sent NAK -> go to idle */
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else if (state == USI_STATE_NAK)
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{
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usi_state = USI_STATE_IDLE;
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}
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/* sent ACK after SLA+W -> wait for data */
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/* sent ACK after DAT+W -> wait for more data */
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else if ((state == USI_STATE_SLAW_ACK) ||
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(state == USI_STATE_DATW_ACK)
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)
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{
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usi_state = USI_STATE_DATW | USI_ENABLE_SCL_HOLD;
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}
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/* data received -> send ACK/NAK */
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else if (state == USI_STATE_DATW)
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{
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if (TWI_data_write(bcnt++, data))
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{
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usi_state = USI_STATE_DATW_ACK | USI_WAIT_FOR_ACK | USI_ENABLE_SDA_OUTPUT | USI_ENABLE_SCL_HOLD;
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USIDR = 0x00;
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}
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else
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{
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usi_state = USI_STATE_NAK | USI_WAIT_FOR_ACK | USI_ENABLE_SDA_OUTPUT | USI_ENABLE_SCL_HOLD;
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USIDR = 0x80;
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}
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}
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/* sent ACK after SLA+R -> send data */
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/* received ACK after DAT+R -> send more data */
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else if ((state == USI_STATE_SLAR_ACK) ||
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((state == USI_STATE_DATR_ACK) && !(data & 0x01))
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)
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{
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USIDR = TWI_data_read(bcnt++);
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usi_state = USI_STATE_DATR | USI_ENABLE_SDA_OUTPUT | USI_ENABLE_SCL_HOLD;
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}
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/* sent data after SLA+R -> receive ACK/NAK */
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else if (state == USI_STATE_DATR)
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{
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usi_state = USI_STATE_DATR_ACK | USI_WAIT_FOR_ACK | USI_ENABLE_SCL_HOLD;
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USIDR = 0x80;
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}
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/* received NAK after DAT+R -> go to idle */
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else if ((state == USI_STATE_DATR_ACK) && (data & 0x01))
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{
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usi_state = USI_STATE_IDLE;
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}
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/* default -> go to idle */
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else
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{
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usi_state = USI_STATE_IDLE;
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}
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/* set SDA direction according to current state */
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if (usi_state & USI_ENABLE_SDA_OUTPUT)
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{
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USI_PIN_SDA_OUTPUT();
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}
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else
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{
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USI_PIN_SDA_INPUT();
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}
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if (usi_state & USI_ENABLE_SCL_HOLD)
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{
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/* Enable TWI Mode, hold SCL low after counter overflow, count both SCL edges */
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USICR = (1<<USIWM1) | (1<<USIWM0) | (1<<USICS1);
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}
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else
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{
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/* Enable TWI, hold SCL low only after start condition, count both SCL edges */
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USICR = (1<<USIWM1) | (1<<USICS1);
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}
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/* clear start/overflow/stop condition flags */
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usisr &= ((1<<USISIF) | (1<<USIOIF) | (1<<USIPF));
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if (usi_state & USI_WAIT_FOR_ACK)
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{
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/* count 2 SCL edges (ACK/NAK bit) */
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USISR = usisr | ((16 -2)<<USICNT0);
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}
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else
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{
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/* count 16 SCL edges (8bit data) */
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USISR = usisr | ((16 -16)<<USICNT0);
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}
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} /* usi_statemachine */
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#endif /* defined (USICR) */
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/* *************************************************************************
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@ -558,16 +740,30 @@ int main(void)
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#error "TCCR0(B) not defined"
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#endif
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#if defined (TWCR)
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/* TWI init: set address, auto ACKs */
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TWAR = (TWI_ADDRESS<<1);
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TWCR = (1<<TWEA) | (1<<TWEN);
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#elif defined (USICR)
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USI_PIN_INIT();
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usi_statemachine(0x00);
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#else
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#error "No TWI/USI peripheral found"
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#endif
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while (cmd != CMD_BOOT_APPLICATION)
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{
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#if defined (TWCR)
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if (TWCR & (1<<TWINT))
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{
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TWI_vect();
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}
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#elif defined (USICR)
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if (USISR & ((1<<USISIF) | (1<<USIOIF) | (1<<USIPF)))
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{
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usi_statemachine(USISR);
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}
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#endif
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#if defined (TIFR)
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if (TIFR & (1<<TOV0))
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@ -586,8 +782,13 @@ int main(void)
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#endif
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}
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#if defined (TWCR)
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/* Disable TWI but keep address! */
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TWCR = 0x00;
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#elif defined (USICR)
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/* Disable USI peripheral */
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USICR = 0x00;
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#endif
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/* disable timer0 */
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#if defined (TCCR0)
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