Added option for writes to specify a SPI speed

3 files changed, 29 insertions, 8 deletions

diff --git a/host/include/uhd/types/serial.hpp b/host/include/uhd/types/serial.hpp
index 7b565c633..5b7f34fbd 100644
--- a/host/include/uhd/types/serial.hpp
+++ b/host/include/uhd/types/serial.hpp
@@ -118,13 +118,19 @@ namespace uhd{
         //! on what edge is the miso data valid?
         edge_t miso_edge;
 
+        //! Set the clock speed for this transaction
+        bool use_custom_divider;
+
+        //! Optionally set the SPI clock divider for this transaction
+        size_t divider;
+
         /*!
          * Create a new spi config.
          * \param edge the default edge for mosi and miso
          */
         spi_config_t(edge_t edge = EDGE_RISE);
     };
-    
+
     /*!
      * The SPI interface class.
      * Provides routines to transact SPI and do other useful things which haven't been defined yet.
diff --git a/host/lib/types/serial.cpp b/host/lib/types/serial.cpp
index 9b8336dd8..52961691c 100644
--- a/host/lib/types/serial.cpp
+++ b/host/lib/types/serial.cpp
@@ -40,7 +40,8 @@ spi_config_t::spi_config_t(edge_t edge):
     mosi_edge(edge),
     miso_edge(edge)
 {
-    /* NOP */
+    // By default don't use a custom clock speed for the transaction
+    use_custom_divider = false;
 }
 
 void i2c_iface::write_eeprom(
diff --git a/host/lib/usrp/cores/spi_core_3000.cpp b/host/lib/usrp/cores/spi_core_3000.cpp
index 0656d910a..d33624b0d 100644
--- a/host/lib/usrp/cores/spi_core_3000.cpp
+++ b/host/lib/usrp/cores/spi_core_3000.cpp
@@ -34,7 +34,7 @@ class spi_core_3000_impl : public spi_core_3000
 {
 public:
     spi_core_3000_impl(wb_iface::sptr iface, const size_t base, const size_t readback):
-        _iface(iface), _base(base), _readback(readback), _ctrl_word_cache(0)
+        _iface(iface), _base(base), _readback(readback), _ctrl_word_cache(0), _divider_cache(0)
     {
         this->set_divider(30);
     }
@@ -46,7 +46,21 @@ public:
         size_t num_bits,
         bool readback
     ){
-        boost::mutex::scoped_lock lock(_mutex);
+        boost::lock_guard<boost::mutex> lock(_mutex);
+
+        //load SPI divider
+        size_t spi_divider = _div;
+        if (config.use_custom_divider) {
+            //The resulting SPI frequency will be f_system/(2*(divider+1))
+            //This math ensures the frequency will be equal to or less than the target
+            spi_divider = (config.divider-1)/2;
+        }
+
+        //conditionally send SPI divider
+        if (spi_divider != _divider_cache) {
+            _iface->poke32(SPI_DIV, spi_divider);
+            _divider_cache = spi_divider;
+        }
 
         //load control word
         boost::uint32_t ctrl_word = 0;
@@ -55,17 +69,16 @@ public:
         if (config.mosi_edge == spi_config_t::EDGE_FALL) ctrl_word |= (1 << 31);
         if (config.miso_edge == spi_config_t::EDGE_RISE) ctrl_word |= (1 << 30);
 
-        //load data word (must be in upper bits)
-        const boost::uint32_t data_out = data << (32 - num_bits);
-
         //conditionally send control word
         if (_ctrl_word_cache != ctrl_word)
         {
-            _iface->poke32(SPI_DIV, _div);
             _iface->poke32(SPI_CTRL, ctrl_word);
             _ctrl_word_cache = ctrl_word;
         }
 
+        //load data word (must be in upper bits)
+        const boost::uint32_t data_out = data << (32 - num_bits);
+
         //send data word
         _iface->poke32(SPI_DATA, data_out);
 
@@ -91,6 +104,7 @@ private:
     boost::uint32_t _ctrl_word_cache;
     boost::mutex _mutex;
     size_t _div;
+    size_t _divider_cache;
 };
 
 spi_core_3000::sptr spi_core_3000::make(wb_iface::sptr iface, const size_t base, const size_t readback)