From 38b4eb1f7fa87079a5a40f5d2ec4b5c0c7f14a4b Mon Sep 17 00:00:00 2001 From: "Mark A. Greer" Date: Tue, 2 Sep 2014 15:12:25 -0700 Subject: [PATCH] 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: Mark A. Greer Signed-off-by: Samuel Ortiz --- drivers/nfc/trf7970a.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/drivers/nfc/trf7970a.c b/drivers/nfc/trf7970a.c index 22485e7..b67946c 100644 --- a/drivers/nfc/trf7970a.c +++ b/drivers/nfc/trf7970a.c @@ -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 -- 2.7.4