arch/esp32_spi: Add check to see if the TX_FIFO is empty

to avoid sending empty data

Signed-off-by: nuttxs <zhaoqing.zhang@sony.com>

arch/xtensa/src/esp32/esp32_spi.c

@@ -849,6 +849,7 @@ static void esp32_spi_dma_exchange(struct esp32_spi_priv_s *priv,
   const uintptr_t spi_miso_dlen_reg = SPI_MISO_DLEN_REG(id);
   const uintptr_t spi_user_reg = SPI_USER_REG(id);
   const uintptr_t spi_cmd_reg = SPI_CMD_REG(id);
+  const uintptr_t spi_dma_rstatus = SPI_DMA_RSTATUS_REG(id);
 
   DEBUGASSERT((txbuffer != NULL) || (rxbuffer != NULL));
 
@@ -940,6 +941,16 @@ static void esp32_spi_dma_exchange(struct esp32_spi_priv_s *priv,
           esp32_spi_reset_regbits(spi_user_reg, SPI_USR_MISO_M);
         }
 
+      if (priv->config->flags & ESP32_SPI_IO_W)
+        {
+          /* Wait until SPI TX FIFO is not empty */
+
+          while ((getreg32(spi_dma_rstatus) & SPI_DMA_TX_FIFO_EMPTY) != 0)
+            {
+              ;
+            }
+        }
+
       esp32_spi_set_regbits(spi_cmd_reg, SPI_USR_M);
 
       esp32_spi_sem_waitdone(priv);

arch/xtensa/src/esp32/hardware/esp32_spi.h

@@ -2782,6 +2782,8 @@
 #define SPI_DMA_RSTATUS_OFFSET  (0x148)
 #define SPI_DMA_RSTATUS_REG(i)  (REG_SPI_BASE(i) + SPI_DMA_RSTATUS_OFFSET)
 
+#define SPI_DMA_TX_FIFO_EMPTY   (BIT(31))
+
 /* SPI_DMA_OUT_STATUS : RO ;bitpos:[31:0] ;default: 32'b0 ; */
 
 /* Description: spi dma read data from memory status. */