SPI Send (sizeof) too big

[PLee.3]

Hi, I am wondering if anyone has any experience with HAL SPI as when I try in 16-bit mode to make a single packet of data manually and use (sizeof xxx) it sends 2x data packets to the oscilloscope and when I specify the packet size as "1" I get the correct waveform? I show it below the code and attach the scope readings:-

uint16_t packet;

packet = 0b0111 1111 1000 0000;  // send 8 MSB bits in 16 bit mode

HAL_SPI_Transmit (&hspi1, &packet, sizeof(packet), HAL_MAX_DELAY); // sends 2 packets?
HAL_SPI_Transmit (&hspi1, &packet, 1, HAL_MAX_DELAY); // sends correct 1 packet.

[waclawek.jan]

sizeof(xxx) returns number of bytes xxx occupies, i.e. in case of uint16_t it's 2.

That's why

> it sends 2x data packets

JW

[Andrew Neil]

Documentation should be clearer:

Always give units !

Note also that units are needed for the Timeout parameter.

@Imen.D 

[Imen.D]

Hello,

@Andrew Neil , thank you for your feedback and for helping us improve the ST documentations!

Your request has been escalated via internal ticket number 173729.

(PS: internal ticket number 173729 is only for reference, not available outside of ST).

[waclawek.jan]

Yes, but what are units in this particular case?

Pieces. It even has an abbreviation (pcs). Not an SI unit, though.

Would you be satisfied with this "unit"?

JW

[Andrew Neil]

---

@waclawek.jan wrote:

Yes, but what are units in this particular case?

---

They are multiples of the "data size" set by SPI_InitTypeDef::DataSize

That also needs to be better documented:

  

Is that bits or bytes?

(the values of SPI_Data_Size do suggest that it's bits)

[PLee.3]

Hi, thanks for the information it seems this "sizeof" is an internal HAL based integer which tells the size of a data packet or array so the correct amount of packets can be sent and is 2^16 (65,535).

This means potentially you can have a pointer or array that can be up too 65,535 in length.