From 8f8f780c2bdd95b8609b43d37f9f4982825851d4 Mon Sep 17 00:00:00 2001 From: Olliver Schinagl Date: Fri, 21 Oct 2016 10:48:56 +0200 Subject: [PATCH] drivers: pn532_i2c: Respect proper timing specifications 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 --- libnfc/drivers/pn532_i2c.c | 81 +++++++++++++++++++++++++++++++------- 1 file changed, 67 insertions(+), 14 deletions(-) diff --git a/libnfc/drivers/pn532_i2c.c b/libnfc/drivers/pn532_i2c.c index fe3345c..6315954 100644 --- a/libnfc/drivers/pn532_i2c.c +++ b/libnfc/drivers/pn532_i2c.c @@ -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)); } /**