Optimize SPI transfers

[sandeepmistry]

Combines SERCOM::writeDataSPI and SERCOM::readDataSPI() into a single SERCOM::transferDataSPI method and remove some flags checks.

Needs more testing, so far basic tests with WiFi101 and SD libraries seem ok.

cc/ @cmaglie @agdl

[ArduinoBot]

✅ Build completed.

⬇️ Build URL: http://downloads.arduino.cc/PR/samd/package_samd-b107_index.json

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2. Add the Build URL above in the Additional Boards Manager URLs field, and click OK.
3. Open the Boards Manager (menu Tools->Board->Board Manager...)
4. Install Arduino SAMD core - Pull Request Optimize SPI transfers #180
5. Select one of the boards under SAMD Pull Request Optimize SPI transfers #180 in Tools->Board menu
6. Compile/Upload as usual

[dlabun]

Is it possible to take the optimizations one (major) step further and introduce DMA?

[ArduinoBot]

✅ Build completed.

⬇️ Build URL: http://downloads.arduino.cc/PR/samd/package_samd-b108_index.json

ℹ️ To test this build:

1. Open the Preferences of the Arduino IDE.
2. Add the Build URL above in the Additional Boards Manager URLs field, and click OK.
3. Open the Boards Manager (menu Tools->Board->Board Manager...)
4. Install Arduino SAMD core - Pull Request Optimize SPI transfers #180
5. Select one of the boards under SAMD Pull Request Optimize SPI transfers #180 in Tools->Board menu
6. Compile/Upload as usual

[sandeepmistry]

@dlabun

Is it possible to take the optimizations one (major) step further and introduce DMA?

It's something to look into later, however due to the blocking nature of the current SPI.transfer(...) API's, I'm not expecting it to yield any performance gains. Also, from testing with the SD and WiFi101 libraries, almost all of the SPI transfers are byte by byte.

[AloyseTech]

Hi guys, I'm working on a DMA Helper to create dedicated DMA library (SPI, I2C, USART...). I have the SPI with DMA working. I still have issue : I can't create an DMA_SPI object in other classes. I think it is a scope issue but I don't have enough knowledge to correctly deal with this issue. ANy help would be appreciated !
Take a look at the source and Unit test here : https://github.com/aloysetech/SAMD_DMA_Helper

[dlabun]

@sandeepmistry
I certainly understand, right now I don't see an issues with writing to my SD card. I do see performance issues with the LCD and that's where I think DMA would help the community.

@AloyseTech
I'm sure I know even less about coding than you, but would certainly test out your library on the Sharp memory LCD once the library is functional.

[ArduinoBot]

✅ Build completed.

⬇️ Build URL: http://downloads.arduino.cc/PR/samd/package_samd-b110_index.json

ℹ️ To test this build:

1. Open the Preferences of the Arduino IDE.
2. Add the Build URL above in the Additional Boards Manager URLs field, and click OK.
3. Open the Boards Manager (menu Tools->Board->Board Manager...)
4. Install Arduino SAMD core - Pull Request Optimize SPI transfers #180
5. Select one of the boards under SAMD Pull Request Optimize SPI transfers #180 in Tools->Board menu
6. Compile/Upload as usual