topic A possible defect of Chip_ADC_SetClockRate() in LPC Microcontrollers

A possible defect of Chip_ADC_SetClockRate()

jeremyhsiao — Mon, 14 Jan 2019 05:33:28 GMT

Hi,

I'm writing to report possible defect of Chip_ADC_SetClockRate() in the LPCOpen 3.03. The content of this function is as below:

Chip_ADC_SetDivider(pADC, ((Chip_Clock_GetSystemClockRate() + (rate>>2)) / rate) -1);

It could mistakenly set up the wrong divider to 0xff when the result of ((Chip_Clock_GetSystemClockRate() + (rate>>2)) / rate) is zero.

In case internal XTAL is used (clock-rate is 12MHz) instead of external clock-rate, the adc demo-code of Init_ADC() will call Chip_ADC_SetClockRate(LPC_ADC, ADC_MAX_CLOCK_RATE), in which ADC_MAX_CLOCK_RATE is 50MHz. This will make result of "((Chip_Clock_GetSystemClockRate() + (rate>>2)) / rate)" as 0. Thus after minus 1 the Divider will be set to 0xff.

It is recommended that some protection or warning is added within Chip_ADC_SetClockRate().

Jeremy

Re: A possible defect of Chip_ADC_SetClockRate()

Alice_Yang — Tue, 15 Jan 2019 03:19:55 GMT

Hello Jeremy,

Thanks for your sharing, could you please tell me the device you are using, I will check it .

Alice

Re: A possible defect of Chip_ADC_SetClockRate()

jeremyhsiao — Tue, 15 Jan 2019 03:49:45 GMT

Hi Alice,

I'm using LPC11U66JBD48 and working on my own board without using external XTAL.

Jeremy

Re: A possible defect of Chip_ADC_SetClockRate()

Alice_Yang — Tue, 15 Jan 2019 09:46:19 GMT

OK, thanks for your recommendation, I have reported it to development team.

Alice