[BUG] MAX31865.cpp implicit truncation results in MINTEMP error

[gth-42]

Did you test the latest bugfix-2.1.x code?

Yes, and the problem still exists.

Bug Description

Compiling MAX31865.cpp without MAX31865_USE_AUTO_MODE produces the warning:

Marlin/src/libs/MAX31865.cpp: In member function 'void MAX31865::begin(max31865_numwires_t, const_float_t, const_float_t, const_float_t)':
Marlin/src/libs/../HAL/shared/Delay.h:167:40: warning: large integer implicitly truncated to unsigned type [-Woverflow]
   #define DELAY_US(x) DELAY_CYCLES((x) * ((F_CPU) / 1000000UL))
                                    ~~~~^~~~~~~~~~~~~~~~~~~~~~~
Marlin/src/libs/MAX31865.cpp:221:5: note: in expansion of macro 'DELAY_US'
     DELAY_US(63000);
     ^~~~~~~~

and immediate MINTEMP error where applicable.
Changing line 199 of src/libs/MAX31865.cpp from DELAY_US(63000) to delay(63) resolves the compile warning and MINTEMP error. Sensing through a MAX31865 then behaves as expected.

Bug Timeline

Unknown (new user)

Expected behavior

Temperature reading through MAX31865.

Actual behavior

Compile warning and MINTEMP error

Steps to Reproduce

Configure to use a MAX31865 and desired sensor. Ensure MAX31865_USE_AUTO_MODE is not enabled. Compile and flash.

Version of Marlin Firmware

bugfix-2.1.x (Mar 20 2025 20:16:36)

Additional information & file uploads

Yes, config is wonky -- trying for minimal

x.zip

.

[thinkyhead]

I'd have to check the data sheet, but 63000 micro-seconds is 63 milliseconds, so it's probably about right for this kind of device. The warning can be eliminated by adding UL suffix to the values. Bare integers are usually native signed int type as defined for the compiler target.

enableBias();
DELAY_US(2000UL); // according to the datasheet, 10.5τ+1msec (see below)
oneShot();
DELAY_US(63000UL);

So then the question is whether this fixes the MINTEMP for you. If it does, then we can apply this patch rather than use what may be a too-small delay.

[gth-42]

Both delay(ms) or the UL suffix to DELAY_US works. Both fix MINTEMP.