Gen3: SPI.transfer() supports accepting const void* parameter.

[XuGuohui]

SPI.transfer takes a void * for the TX buffer. On Gen2 (Electron, etc) SPI.transfer works when casting a const TX buffer (ex. const array, const string, etc) to a non-const TX buffer. On Gen3 this will result in an immediate hard fault and program crash because the nRF SPI DMA function requires the tx buffer to be in RAM.

Change the interface of SPI.transfer to take const void * and to copy the buffer to RAM if it was not in RAM.

Example App

#include "Particle.h"

Serial1LogHandler logHandler(115200, LOG_LEVEL_ALL);

SYSTEM_THREAD(ENABLED);
SYSTEM_MODE(SEMI_AUTOMATIC);

static runtime_info_t heapInfo;

void setup() {
    if (heapInfo.size == 0) {
        heapInfo.size = sizeof(heapInfo);
    }

    HAL_Core_Runtime_Info(&heapInfo, nullptr);
    Log.info("Heapinfo: size :%lu, largest_free_block_heap :%lu", heapInfo.freeheap, heapInfo.largest_free_block_heap);

    SPI.setDataMode(SPI_MODE0);
    SPI.setClockSpeed(100 * 1000);
    SPI.begin();
}

void loop() {
    delay(1000);

    SPI.transfer((uint8_t*) "ABC", NULL, sizeof("ABC"), NULL);
    HAL_Core_Runtime_Info(&heapInfo, nullptr);
    Log.info("Heapinfo: size :%lu, largest_free_block_heap :%lu", heapInfo.freeheap, heapInfo.largest_free_block_heap);
}

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Completeness

• User is totes amazing for contributing!
• Contributor has signed CLA (Info here)
• Problem and Solution clearly stated
• Run unit/integration/application tests on device
• Added documentation
• Added to CHANGELOG.md after merging (add links to docs and issues)

[avtolstoy]

transfer() signature should also reflect these changes. The tx pointer should be const.