STM32G4 DAC output HAL+LL naming

[Michal Dudka]

Hi,

HAL and LL DAC configuration structure and its parameters naming can be confusing. Reference manual claims that DAC "mode" (register ADC->MCR, bits 0..2 or 16..17) can be in one of following four combinations when not used sample and hold mode:
0 -> DAC channel2 is connected to external pin with Buffer enabled
1 -> DAC channel2 is connected to external pin and to on chip peripherals with buffer enabled
2 -> DAC channel2 is connected to external pin with buffer disabled
3 -> DAC channel2 is connected to on chip peripherals with Buffer disabled

These combinations coherent but HAL DAC init struct offers up to six conbinations (Enable/Disable buffer times Internal/External/both connections). Some of them are not accesible. I've listed following configurations:

a) - OK
DAC_OutputBuffer = DAC_OUTPUTBUFFER_ENABLE;
DAC_ConnectOnChipPeripheral = DAC_CHIPCONNECT_EXTERNAL;
Resulting configuration: 0 -> DAC channel2 is connected to external pin with Buffer enabled

b) - Misleading
DAC_OutputBuffer = DAC_OUTPUTBUFFER_ENABLE;
DAC_ConnectOnChipPeripheral = DAC_CHIPCONNECT_INTERNAL;
Resulting configuration: 1 -> DAC channel2 is connected to external pin and to on chip peripherals with buffer enabled

c) - OK
DAC_OutputBuffer = DAC_OUTPUTBUFFER_ENABLE;
DAC_ConnectOnChipPeripheral = DAC_CHIPCONNECT_BOTH;
Resulting configuration: 1 -> DAC channel2 is connected to external pin and to on chip peripherals with buffer enabled

d) - OK
DAC_OutputBuffer = DAC_OUTPUTBUFFER_DISABLE;
DAC_ConnectOnChipPeripheral = DAC_CHIPCONNECT_EXTERNAL;
Resulting configuration: 2 -> DAC channel2 is connected to external pin with buffer disabled

e) - OK
DAC_OutputBuffer = DAC_OUTPUTBUFFER_DISABLE;
DAC_ConnectOnChipPeripheral = DAC_CHIPCONNECT_INTERNAL;
Resulting configuration: 3 -> DAC channel2 is connected to on chip peripherals with Buffer disabled

f) - Misleading
DAC_OutputBuffer = DAC_OUTPUTBUFFER_DISABLE;
DAC_ConnectOnChipPeripheral = DAC_CHIPCONNECT_BOTH;
Resulting configuration: 2 -> DAC channel2 is connected to external pin with buffer disabled


Also LL API have misleading parameter naming:

a) - OK
OutputBuffer = LL_DAC_OUTPUT_BUFFER_ENABLE;
OutputConnection = LL_DAC_OUTPUT_CONNECT_GPIO;
Resulting configuration: 0 -> DAC channel2 is connected to external pin with Buffer enabled

b) - Misleading
OutputBuffer = LL_DAC_OUTPUT_BUFFER_ENABLE;
OutputConnection = LL_DAC_OUTPUT_CONNECT_INTERNAL;
Resulting configuration: 1 -> DAC channel2 is connected to external pin and to on chip peripherals with buffer enabled

c) - OK
OutputBuffer = LL_DAC_OUTPUT_BUFFER_DISABLE;
OutputConnection = LL_DAC_OUTPUT_CONNECT_GPIO;
Resulting configuration: 2 -> DAC channel2 is connected to external pin with buffer disabled

d) - OK
OutputBuffer = LL_DAC_OUTPUT_BUFFER_DISABLE;
OutputConnection = LL_DAC_OUTPUT_CONNECT_INTERNAL;
Resulting configuration: 3 -> DAC channel2 is connected to on chip peripherals with Buffer disabled

You probably should enhance comment of structs
LL_DAC_InitTypeDef
DAC_ChannelConfTypeDef
to cover this confusions. Or/And change macros names. Or better change struct structure to correspond reference manual with four legal combinations.

[Imen.D · Accepted solution]

Hello @Michal Dudka ,

Thank you for having reported your feedback.

I highlighted this request (via the internal ticket number: 181777) to our development team to be analyzed.

(PS: Internal ticket number 181777 is an internal tracking number and is not accessible or usable by customers).

[Imen.D]

Hi @Michal Dudka,

About your reported cases Misleading mentioned in the description:

"b)": not a problem: connection internal requested is provided (with connection to external pin in addition. If needed, can be disconnected from pin by setting GPIO in digital mode)

"f)": indeed this is a problem because connection DAC_CHIPCONNECT_BOTH requested is not provided, connection is only on GPIO(DAC_CHIPCONNECT_EXTERNAL) 

About proposal "...change struct structure to correspond reference manual with four legal combinations": the problem is that depending of mode normal or sample & hold, these 4 combinations are different. 

The 3 parameters {mode; output buffer; connection} are managed in unitary way in drivers:

• LL driver: only connections gpio and internal proposed (not both, since cannot be guaranteed depending on mode selected) and functions LL_DAC_ConfigOutput() and LL_DAC_SetOutputConnection() with description:  

* @note   On this STM32 series, output connection depends on output mode  
*         (normal or sample and hold) and output buffer state.  
*         - if output connection is set to internal path and output buffer  
*           is enabled (whatever output mode):  
*           output connection is also connected to GPIO pin  
*           (both connections to GPIO pin and internal path).  
*         - if output connection is set to GPIO pin, output buffer  
*           is disabled, output mode set to sample and hold:  
*           output connection is also connected to internal path  
*           (both connections to GPIO pin and internal path).

• HAL driver: connection of both modes proposed and description missing.

We propose to update HAL DAC driver: 

• add an assert for misleading case normal mode + buffer disabled +connection both
• add descriptions.