Add a lock around the SPI bus

This seems to have been the cause of recurring deadlocks that have been
difficult to repo.

1 files changed, 6 insertions, 0 deletions

diff --git a/src/drivers/spi.cpp b/src/drivers/spi.cpp
index 93bf9cde..ba461b67 100644
--- a/src/drivers/spi.cpp
+++ b/src/drivers/spi.cpp
@@ -20,6 +20,8 @@ static const gpio_num_t kSpiSdoPin = GPIO_NUM_23;
 static const gpio_num_t kSpiSdiPin = GPIO_NUM_19;
 static const gpio_num_t kSpiSclkPin = GPIO_NUM_18;
 
+static std::mutex sSpiMutex{};
+
 esp_err_t init_spi(void) {
   spi_bus_config_t config = {
       .mosi_io_num = kSpiSdoPin,
@@ -52,4 +54,8 @@ esp_err_t deinit_spi(void) {
   return spi_bus_free(kSpiHost);
 }
 
+std::lock_guard<std::mutex> acquire_spi(void) {
+  return std::lock_guard<std::mutex>{sSpiMutex};
+}
+
 }  // namespace drivers