CryptoAuthLib
Atmel CryptoAuthentication Library
swi_bitbang_at88ck9000.h File Reference

definitions for bit-banged SWI More...

#include "atca_status.h"
#include "timer_utilities.h"

Go to the source code of this file.

Data Structures

struct  SWIBuses
 

Macros

#define MAX_SWI_BUSES   10
 AT88CK9000 has 10 sets of GPIO pin dedicated for SWI. More...
 
Macros for Bit-Banged SWI Timing

Times to drive bits at 230.4 kbps.

#define BIT_DELAY_1L   delay_us(3)
 
#define BIT_DELAY_1H   delay_us(3)
 should be 4.34 us, is 4.42 us More...
 
#define BIT_DELAY_5   delay_us(24)
 
#define BIT_DELAY_7   delay_us(32)
 
#define RX_TX_DELAY   delay_us(14)
 
#define START_PULSE_TIME_OUT   (255)
 
#define ZERO_PULSE_TIME_OUT   (26)
 

Functions

void swi_set_pin (uint8_t id)
 Set SWI signal pin. Other functions will use this pin. More...
 
void swi_enable (void)
 Configure GPIO pin for SWI signal as output. More...
 
void swi_disable (void)
 Configure GPIO pin for SWI signal as input. More...
 
void swi_set_signal_pin (uint8_t is_high)
 Set signal pin Low or High. More...
 
void swi_send_wake_token (void)
 Send a Wake Token. More...
 
void swi_send_bytes (uint8_t count, uint8_t *buffer)
 Send a number of bytes. More...
 
void swi_send_byte (uint8_t byte)
 Send one byte. More...
 
ATCA_STATUS swi_receive_bytes (uint8_t count, uint8_t *buffer)
 Receive a number of bytes. More...
 

Variables

SWIBuses swi_buses_default
 

Detailed Description

definitions for bit-banged SWI

Author
Atmel Crypto Products
Date
November 18, 2015

Macro Definition Documentation

#define BIT_DELAY_1H   delay_us(3)

should be 4.34 us, is 4.42 us

#define BIT_DELAY_1L   delay_us(3)

delay macro for width of one pulse (start pulse or zero pulse) should be 4.34 us, is 4.67 us

#define BIT_DELAY_5   delay_us(24)

time to keep pin high for five pulses plus stop bit (used to bit-bang CryptoAuth 'zero' bit) should be 26.04 us, is 26.42 us

#define BIT_DELAY_7   delay_us(32)

time to keep pin high for seven bits plus stop bit (used to bit-bang CryptoAuth 'one' bit) should be 34.72 us, is 34.75 us

#define MAX_SWI_BUSES   10

AT88CK9000 has 10 sets of GPIO pin dedicated for SWI.

#define RX_TX_DELAY   delay_us(14)

turn around time when switching from receive to transmit should be 15 us, is 15.4 us

#define START_PULSE_TIME_OUT   (255)

One loop iteration for edge detection takes about 0.6 us on this hardware. Lets set the timeout value for start pulse detection to the uint8_t maximum. This value is decremented while waiting for the falling edge of a start pulse.

#define ZERO_PULSE_TIME_OUT   (26)

We measured a loop count of 8 for the start pulse. That means it takes about 0.6 us per loop iteration. Maximum time between rising edge of start pulse and falling edge of zero pulse is 8.6 us. Therefore, a value of 26 (around 15 us) gives ample time to detect a zero pulse and also leaves enough time to detect the following start pulse. The values above were established using the WinAVR 2010 compiler. The code runs faster when compiled with the compiler version of Atmel Studio 6. In this case a timeout value of 26 leads to a timeout of 10 us which is still greater than 8.6 us. This value is decremented while waiting for the falling edge of a zero pulse.

Function Documentation

void swi_disable ( void  )

Configure GPIO pin for SWI signal as input.

void swi_enable ( void  )

Configure GPIO pin for SWI signal as output.

ATCA_STATUS swi_receive_bytes ( uint8_t  count,
uint8_t *  buffer 
)

Receive a number of bytes.

Parameters
[in]countnumber of bytes to receive
[out]bufferpointer to receive buffer
Returns
ATCA_STATUS

Receive bits and store in buffer.

Make sure that the variable below is big enough. Change it to uint16_t if 255 is too small, but be aware that the loop resolution decreases on an 8-bit controller in that case.

Detect start bit.

Wait for falling edge.

Wait for rising edge.

For an Atmel microcontroller this might be faster than "pulse_count++".

Trying to measure the time of start bit and calculating the timeout for zero bit detection is not accurate enough for an 8 MHz 8-bit CPU. So let's just wait the maximum time for the falling edge of a zero bit to arrive after we have detected the rising edge of the start bit.

Detect possible edge indicating zero bit.

For an Atmel microcontroller this might be faster than "pulse_count++".

Wait for rising edge of zero pulse before returning. Otherwise we might interpret its rising edge as the next start pulse.

Update byte at current buffer index.

received "one" bit

Indicate that we timed out after having received at least one byte.

void swi_send_byte ( uint8_t  byte)

Send one byte.

Parameters
[in]bytebyte to send
void swi_send_bytes ( uint8_t  count,
uint8_t *  buffer 
)

Send a number of bytes.

Parameters
[in]countnumber of bytes to send.
[in]bufferpointer to buffer containing bytes to send

Wait turn around time.

< Send Logic 1 (7F)

< Send Logic 0 (7D)

void swi_send_wake_token ( void  )

Send a Wake Token.

void swi_set_pin ( uint8_t  id)

Set SWI signal pin. Other functions will use this pin.

Parameters
[in]iddefinition of GPIO pin to be used
void swi_set_signal_pin ( uint8_t  is_high)

Set signal pin Low or High.

Parameters
[in]is_high0: Low, else: High.

Variable Documentation

SWIBuses swi_buses_default