On Tue, Jun 15, 2021 at 11:34:53PM +0000, Chris Packham wrote: > Hi Guenter, > > I've had a report from someone testing the BPA-RS600. > > When they have the input voltage set to >= 256V (apparently the PSU can > handle input up to 264V). The Vin reading goes negative. > > CMD 0x88, VAL=0xf3f8, Vin=254 > CMD 0x88, VAL=0xf3fc, Vin=255 > CMD 0x88, VAL=0xf400, Vin=-256 > > Looking at pmbus_reg2data_linear() the mantissa is cast to s16 which is > correct according to section 7.1 of the PMBUS spec which says that the > mantissa is an 11-bit two's complement value. > > It seems that the BPA-RS600 is using a non-standard format for the > mantissa (probably because the range of the standard linear encoding > can't support values >255V). Does the pmbus infrastructure provide a way > for me to define a custom format/conversion for a given sensor? Essentially you'll have to implement a custom read word function and convert the value reported by the power supply to a valid linear11 value. In this case, you may have to shift the reported value by 1 bit and increase the exponent by one. Not sure what you mean with "standard linear encoding can't support values >255V". Why not ? That is what the exponent is for, after all. It rather seems to me that the PS vendor decided to violate the standard to get another bit of accuracy. Guenter
