Slower SPI speed for MAX31855 #3888
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| @@ -1161,7 +1163,7 @@ void Temperature::disable_all_heaters() { | |||
| PRR0 | |||
| #endif | |||
| , PRSPI); | |||
| SPCR = _BV(MSTR) | _BV(SPE) | _BV(SPR0); | |||
| SPCR = _BV(MSTR) | _BV(SPE) | MAX6675_SPEED_BITS; | |||
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Are we sure the sd-library initialises SPCR for every use (read/write) or does it make sense to store it here and restore later
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I was wondering something similar. Would this be moved to the Temperature::init method (to only be initialized once)? Or… is there another approach you have in mind?
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Since we don't yet know the answer to this, I will merge for now.
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Background: According to investigation by @Grogyan at #3548 the SPI speed is just a little too fast to read the MAX31855 thermocouple reliably. This might also apply to the MAX6675, but we haven't had any reports to that effect. So this PR supplies a patch for the MAX31855 only.
Solution: For the MAX31855 the SPI clock divider is set to 64. The MAX6675 still uses an SPI clock divider of 16.