SPI.transfer(buffer, size) is missing

[PaulStoffregen]

ESP32's SPI library is missing overloaded function SPI.transfer(buffer, size).

Here is Arduino's documentation.

https://www.arduino.cc/en/Reference/SPITransfer

Arduino sketches and libraries using this function will not compile for ESP32. This is a very easy fix, just add this line in SPI.h

  void transfer(uint8_t * data, uint32_t size) { transferBytes(data, data, size); }

[me-no-dev]

why not make a PR 😄

[me-no-dev]

don't implement it in the header like that though

[PaulStoffregen]

I released Arduino Ethernet 2.0.0 today.
https://github.com/arduino-libraries/Ethernet/releases/tag/2.0.0

It requires this issue fixed to compile for ESP32. Users can of course still use the old versions, or Adafruit's Ethernet2 or others... without the improvement performance and new features.

[iafilius]

Hi, just a "me too" message (for libaries 1.0.0 and 1.0.1-rc1). The quick fix by adding the oneliner to SPI.h worked for me.

[iafilius]

Hi, created pull request #2136 for it. I hope the fix makes it into 1.0.1-rc2. Regards

[PaulStoffregen]

While not strictly necessary to get Ethernet to work, you will see slightly improved performance on the W5500 chip if you also add SPI.transfer(const void *txBuffer, void *rxBuffer, size_t count) and define SPI_HAS_TRANSFER_BUF.

Here's where it's actually used by the Ethernet library:
https://github.com/arduino-libraries/Ethernet/blob/master/src/utility/w5100.cpp#L372

If SPI.h does not have this function, Ethernet will revert to using single byte transfers.

[iafilius]

@me-no-dev Thanks for accepting accepting the commit

@PaulStoffregen ,

you mean something like:

SPI.h:
class SPIClass
<>
public:
<>
void transfer(const void * txBuffer, const void * rxBuffer, uint32_t size);
<>

SPI.cpp:

// SPI_HAS_TRANSFER_BUF - is defined to signify that this library supports
// a version of transfer which allows you to pass in both TX and RX buffer
// pointers, either of which could be NULL
#define SPI_HAS_TRANSFER_BUF 1
SPI.transfer(const void *txBuffer, void *rxBuffer, size_t count)
{
transferBytes(txBuffer, rxBuffer, size);
}

If i see it correctly, no corresponding transferBytes() is available with the right types (void*), and no void* type parameter functions are available yet. What do you have in mind?
Regards

[PaulStoffregen]

Yes, about like that. The pointers are void, so not necessarily aligned to 32 bit boundaries (was an issue on ESP8266).

[Popcron07]

Hi, I ran into a problem which I think might have something to do with your changes.
When I try to compile my code I get this error message:

C:...\packages\esp32\hardware\esp32\1.0.0\libraries\SPI\src/SPI.h:69:13: note: candidate: uint8_t SPIClass::transfer(uint8_t)

 uint8_t transfer(uint8_t data);

         ^

C:...\packages\esp32\hardware\esp32\1.0.0\libraries\SPI\src/SPI.h:69:13: note: candidate expects 1 argument, 2 provided

@iafilius wrote it is strange to give the data twice and I think that is why I am not able to compile.
So please tell me, is this the cause for my error or do I have to search for something else?

Also I think this fellow might have the same problem and it really fits because his post is just a week old, too:
https://stackoverflow.com/questions/53795074/arduino-exit-status-1

Regards, Popcorn

[iafilius]

Hi @Popcron07 , with not much info to work on, I see you're Using 1.0.0 libary. The Arduino dev/prerelease version i used was 1.0.1-rc1 prerelease, but the proposed fix of missing "SPI.transfer(buffer, size) is missing #1623" was pulled afterwards. This is the issue you seem to have. (As I did)

I case you're interested I wrote some demo code for using the W5500 and WiFi and using NTP as sample ethernet traffic.
You can find it on:
https://github.com/iafilius/ESP32_W5500_Ethernet_NTP_deepsleep_demo
It needs the fix, proposed by @PaulStoffregen, which i just created the pull request based on. .

So you or simply Apply PaulStofregen's patch, or my version into current libary and you're probably good to go. I see current prerelease 1.0.1-rc2 is available and included this fix. It is listen in the changelog as:
b5f3170 Fixed Arduino SPI/Ethernet compile issue as described in issue #1623 (#2136)

Does this help you?

Regards,
Arjan