diff options
Diffstat (limited to 'drivers/nfc/trf7970a.c')
| -rw-r--r-- | drivers/nfc/trf7970a.c | 15 |
1 files changed, 12 insertions, 3 deletions
diff --git a/drivers/nfc/trf7970a.c b/drivers/nfc/trf7970a.c index 22485e703849..b67946c18b40 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 |