crewID/libnfc
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

drivers: pn532_i2c: Respect proper timing specifications

Browse source 
The pn532 user manual states that after a i2c stop condition and before a i2c
start condition there should be a delay of minimally 1.3 milliseconds.
This is probably a limitation of the i2c peripheral or the firmware. In
any case, each i2c_read and i2c_write creates the packets which are
complemented with start/stop markers. It is thus required to take care
of timing in these two functions.

We solve this by wrapping the lower i2c_read and i2c_write functions for
the pn532, as this requirement is not for all chips.

Currently, we keep time using local variable, and thus the code is not
thread-safe. With libnfc being single threaded and only one instances of
libnfc can open a bus anyway, this is not yet a problem.

Signed-off-by: Olliver Schinagl <oliver@schinagl.nl>
This commit is contained in:
Olliver Schinagl 2016-10-21 10:48:56 +02:00
parent b953002f8f
commit 8f8f780c2b
1 changed files with 67 additions and 14 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

81
libnfc/drivers/pn532_i2c.c
View file

@ -67,14 +67,6 @@ struct pn532_i2c_data {
volatile bool abort_flag;
};
/* Delay for the loop waiting for READY frame (in ms) */
#define PN532_RDY_LOOP_DELAY 90
const struct timespec rdyDelay = {
.tv_sec = 0,
.tv_nsec = PN532_RDY_LOOP_DELAY * 1000 * 1000
};
/* preamble and start bytes, see pn532-internal.h for details */
const uint8_t pn53x_preamble_and_start[] = { 0x00, 0x00, 0xff };
#define PN53X_PREAMBLE_AND_START_LEN (sizeof(pn53x_preamble_and_start) / sizeof(pn53x_preamble_and_start[0]))
@ -100,6 +92,70 @@ static size_t pn532_i2c_scan(const nfc_context *context, nfc_connstring connstri
#define DRIVER_DATA(pnd) ((struct pn532_i2c_data*)(pnd->driver_data))
/*
* Bus free time (in ms) between a STOP condition and START condition. See
* tBuf in the PN532 data sheet, section 12.25: Timing for the I2C interface,
* table 320. I2C timing specification, page 211, rev. 3.2 - 2007-12-07.
*/
#define PN532_BUS_FREE_TIME 1.3
static struct timespec __transaction_stop;
/**
* @brief Wrapper around i2c_read to ensure proper timing by respecting the
* minimal free bus time between a STOP condition and a START condition.
*
* @note This is not thread safe, but since libnfc is single threaded
* this should be okay.
*
* @param id I2C device
* @param buf pointer on buffer used to store data
* @param len length of the buffer
* @return length (in bytes) of read data, or driver error code (negative value)
*/
static ssize_t pn532_i2c_read(const i2c_device id,
uint8_t *buf, const size_t len)
{
struct timespec transaction_start, bus_free_time = { 0 };
ssize_t ret;
clock_gettime(CLOCK_MONOTONIC, &transaction_start);
bus_free_time.tv_nsec = (PN532_BUS_FREE_TIME * 1000 * 1000) -
(transaction_start.tv_nsec - __transaction_stop.tv_nsec);
nanosleep(&bus_free_time, NULL);
ret = i2c_read(id, buf, len);
clock_gettime(CLOCK_MONOTONIC, &__transaction_stop);
return ret;
}
/**
* @brief Wrapper around i2c_write to ensure proper timing by respecting the
* minimal free bus time between a STOP condition and a START condition.
*
* @note This is not thread safe, but since libnfc is single threaded
* this should be okay.
*
* @param id I2C device
* @param buf pointer on buffer containing data
* @param len length of the buffer
* @return NFC_SUCCESS on success, otherwise driver error code
*/
static ssize_t pn532_i2c_write(const i2c_device id,
const uint8_t *buf, const size_t len)
{
struct timespec transaction_start, bus_free_time = { 0 };
ssize_t ret;
clock_gettime(CLOCK_MONOTONIC, &transaction_start);
bus_free_time.tv_nsec = (PN532_BUS_FREE_TIME * 1000 * 1000) -
(transaction_start.tv_nsec - __transaction_stop.tv_nsec);
nanosleep(&bus_free_time, NULL);
ret = i2c_write(id, buf, len);
clock_gettime(CLOCK_MONOTONIC, &__transaction_stop);
return ret;
}
/**
* @brief Scan all available I2C buses to find PN532 devices.
*
@ -347,7 +403,7 @@ pn532_i2c_send(nfc_device *pnd, const uint8_t *pbtData, const size_t szData, int
return pnd->last_error;
}
res = i2c_write(DRIVER_DATA(pnd)->dev, abtFrame, szFrame);
res = pn532_i2c_write(DRIVER_DATA(pnd)->dev, abtFrame, szFrame);
if (res < 0) {
log_put(LOG_GROUP, LOG_CATEGORY, NFC_LOG_PRIORITY_ERROR, "%s", "Unable to transmit data. (TX)");
@ -405,10 +461,7 @@ pn532_i2c_wait_rdyframe(nfc_device *pnd, uint8_t *pbtData, const size_t szDataLe
}
do {
// Wait a little bit before reading
nanosleep(&rdyDelay, (struct timespec *) NULL);
int recCount = i2c_read(DRIVER_DATA(pnd)->dev, i2cRx, szDataLen + 1);
int recCount = pn532_i2c_read(DRIVER_DATA(pnd)->dev, i2cRx, szDataLen + 1);
if (DRIVER_DATA(pnd)->abort_flag) {
// Reset abort flag
@ -575,7 +628,7 @@ error:
int
pn532_i2c_ack(nfc_device *pnd)
{
return i2c_write(DRIVER_DATA(pnd)->dev, pn53x_ack_frame, sizeof(pn53x_ack_frame));
return pn532_i2c_write(DRIVER_DATA(pnd)->dev, pn53x_ack_frame, sizeof(pn53x_ack_frame));
}
/**