From 6ba23bafe2abdbacc6aeaffbc6bd093487c33f71 Mon Sep 17 00:00:00 2001 From: "David A. Mellis" Date: Sat, 20 Jun 2009 20:43:24 +0000 Subject: [PATCH] Fixing bug in Wire library that caused it to read and discard one extra byte when do a requestFrom() a slave device. Thanks to Christopher K. Johnson. --- hardware/libraries/Wire/utility/twi.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/hardware/libraries/Wire/utility/twi.c b/hardware/libraries/Wire/utility/twi.c index 82a25c043..bfa917a8d 100644 --- a/hardware/libraries/Wire/utility/twi.c +++ b/hardware/libraries/Wire/utility/twi.c @@ -135,7 +135,12 @@ uint8_t twi_readFrom(uint8_t address, uint8_t* data, uint8_t length) // initialize buffer iteration vars twi_masterBufferIndex = 0; - twi_masterBufferLength = length; + twi_masterBufferLength = length-1; // This is not intuitive, read on... + // On receive, the previously configured ACK/NACK setting is transmitted in + // response to the received byte before the interrupt is signalled. + // Therefor we must actually set NACK when the _next_ to last byte is + // received, causing that NACK to be sent in response to receiving the last + // expected byte of data. // build sla+w, slave device address + w bit twi_slarw = TW_READ;