From 5999a468ac68be56c2ee95b82e5715e4e7b7bb7e Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <tridge@samba.org>
Date: Fri, 15 Nov 2013 17:45:02 +1100
Subject: [PATCH] HAL_AVR: force all devices on SPI0 to low speed when one is
 low speed

this forces MS5611 to low speed when MPU6K is low speed
---
 libraries/AP_HAL_AVR/SPIDevice_SPI0.cpp | 6 ++++++
 libraries/AP_HAL_AVR/SPIDevices.h       | 1 +
 2 files changed, 7 insertions(+)

diff --git a/libraries/AP_HAL_AVR/SPIDevice_SPI0.cpp b/libraries/AP_HAL_AVR/SPIDevice_SPI0.cpp
index e52b95421c..4cc2afcefe 100644
--- a/libraries/AP_HAL_AVR/SPIDevice_SPI0.cpp
+++ b/libraries/AP_HAL_AVR/SPIDevice_SPI0.cpp
@@ -17,6 +17,7 @@ extern const AP_HAL::HAL& hal;
 #define SPI0_SCK_PIN  52
 
 AVRSemaphore AVRSPI0DeviceDriver::_semaphore;
+bool AVRSPI0DeviceDriver::_force_low_speed;
 
 static volatile bool spi0_transferflag = false;
 
@@ -40,6 +41,9 @@ void AVRSPI0DeviceDriver::_cs_assert()
 {
     const uint8_t valid_spcr_mask = 
         (_BV(CPOL) | _BV(CPHA) | _BV(SPR1) | _BV(SPR0));
+    if (_force_low_speed) {
+        _spcr = _spcr_lowspeed;
+    }
     uint8_t new_spcr = (SPCR & ~valid_spcr_mask) | (_spcr & valid_spcr_mask);
     SPCR = new_spcr;  
 
@@ -145,8 +149,10 @@ void AVRSPI0DeviceDriver::set_bus_speed(AVRSPI0DeviceDriver::bus_speed speed)
 {
     if (speed == AVRSPI0DeviceDriver::SPI_SPEED_HIGH) {
         _spcr = _spcr_highspeed;
+        _force_low_speed = false;
     } else {
         _spcr = _spcr_lowspeed;
+        _force_low_speed = true;
     }
 }
 
diff --git a/libraries/AP_HAL_AVR/SPIDevices.h b/libraries/AP_HAL_AVR/SPIDevices.h
index 021fd645ce..f28059c242 100644
--- a/libraries/AP_HAL_AVR/SPIDevices.h
+++ b/libraries/AP_HAL_AVR/SPIDevices.h
@@ -39,6 +39,7 @@ private:
     void _transfer16(const uint8_t *tx, uint8_t *rx);
 
     static AP_HAL_AVR::AVRSemaphore _semaphore;
+    static bool _force_low_speed;
 
     AP_HAL_AVR::AVRDigitalSource *_cs_pin;
     const uint8_t _spcr_lowspeed;