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NFC: trf7970a: Recalculate driver timeout values

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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: Mark A. Greer <mgreer@animalcreek.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
This commit is contained in:
Mark A. Greer 2014-09-02 15:12:25 -07:00 committed by Samuel Ortiz
parent 4e64eff837
commit 38b4eb1f7f
1 changed files with 12 additions and 3 deletions
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15
drivers/nfc/trf7970a.c
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@ -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