From 53a8aeb6e7a89ad169ad3f9e5553d51fb86c03b8 Mon Sep 17 00:00:00 2001
From: Damien George <damien.p.george@gmail.com>
Date: Wed, 3 Jun 2015 23:20:23 +0100
Subject: [PATCH] stmhal: Fix slow SPI DMA transfers by removing wfi from DMA
 wait loop.

Addresses issue #1268.
---
 stmhal/spi.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/stmhal/spi.c b/stmhal/spi.c
index da24b701fc..19c36d0a3b 100644
--- a/stmhal/spi.c
+++ b/stmhal/spi.c
@@ -290,12 +290,14 @@ void spi_deinit(SPI_HandleTypeDef *spi) {
 }
 
 STATIC HAL_StatusTypeDef spi_wait_dma_finished(SPI_HandleTypeDef *spi, uint32_t timeout) {
+    // Note: we can't use WFI to idle in this loop because the DMA completion
+    // interrupt may occur before the WFI.  Hence we miss it and have to wait
+    // until the next sys-tick (up to 1ms).
     uint32_t start = HAL_GetTick();
     while (HAL_SPI_GetState(spi) != HAL_SPI_STATE_READY) {
         if (HAL_GetTick() - start >= timeout) {
             return HAL_TIMEOUT;
         }
-        __WFI();
     }
     return HAL_OK;
 }