Commit 38b4eb1f authored by Mark A. Greer's avatar Mark A. Greer Committed by Samuel Ortiz
Browse files

NFC: trf7970a: Recalculate driver timeout values 



Some of the timeout values used in the driver
are not long enough to handle worst-case scenarios
so they need to be recalculated.

The time to wait for the FIFO to drain past the
low-watermark is now 20 ms because it can take
around 14.35 ms to send 95 bytes (127 bytes in
full FIFO minus 32 bytes where the low-watermark
interrupt will fire).  95 bytes will take around
14.35 ms at 6.62 kbps (the lowest supported bit
rate used by ISO/IEC 15693) so 20 ms should be a
safe value.

The time to wait before issuing an EOF to complete
an ISO/IEC 15693 write or lock command is 40 ms--
20 ms to drain the FIFO and another 20 ms to ensure
the wait is long enough before sending an EOF.

Signed-off-by: default avatarMark A. Greer <mgreer@animalcreek.com>
Signed-off-by: default avatarSamuel Ortiz <sameo@linux.intel.com>
parent 4e64eff8

drivers/nfc/trf7970a.c

+12 −3
Original line number Diff line number Diff line
@@ -83,6 +83,13 @@ 
 * been received and there isn't an error).  The delay is 20 ms since delays

 * of ~16 ms have been observed during testing.

 *

 * When transmitting a frame larger than the FIFO size (127 bytes), the

 * driver will wait 20 ms for the FIFO to drain past the low-watermark

 * and generate an interrupt.  The low-watermark set to 32 bytes so the

 * interrupt should fire after 127 - 32 = 95 bytes have been sent.  At

 * the lowest possible bit rate (6.62 kbps for 15693), it will take up

 * to ~14.35 ms so 20 ms is used for the timeout.

 *

 * Type 2 write and sector select commands respond with a 4-bit ACK or NACK.

 * Having only 4 bits in the FIFO won't normally generate an interrupt so

 * driver enables the '4_bit_RX' bit of the Special Functions register 1
@@ -105,7 +112,9 @@ 
 * Note under Table 1-1 in section 1.6 of

 * http://www.ti.com/lit/ug/scbu011/scbu011.pdf, that wait should be at least

 * 10 ms for TI Tag-it HF-I tags; however testing has shown that is not long

 * enough.  For this reason, the driver waits 20 ms which seems to work

 * enough so 20 ms is used.  So the timer is set to 40 ms - 20 ms to drain

 * up to 127 bytes in the FIFO at the lowest bit rate plus another 20 ms to

 * ensure the wait is long enough before sending the EOF.  This seems to work

 * reliably.

 */
@@ -131,8 +140,8 @@ 
#define TRF7970A_TX_MAX				(4096 - 1)



#define TRF7970A_WAIT_FOR_RX_DATA_TIMEOUT	20

#define TRF7970A_WAIT_FOR_FIFO_DRAIN_TIMEOUT	3

#define TRF7970A_WAIT_TO_ISSUE_ISO15693_EOF	20

#define TRF7970A_WAIT_FOR_FIFO_DRAIN_TIMEOUT	20

#define TRF7970A_WAIT_TO_ISSUE_ISO15693_EOF	40



/* Guard times for various RF technologies (in us) */

#define TRF7970A_GUARD_TIME_NFCA		5000

CRA Git | Maintained and supported by SUSTech CRA and CCSE