Diff: SSEL_spi.h

Revision:

0:9fa30f3069ae

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/SSEL_spi.h	Sat Mar 22 18:57:17 2014 +0000
@@ -0,0 +1,107 @@
+/* Class SSEL_spi, Copyright 2014, David T. Mort (http://mbed.org/users/dtmort/)
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+#ifndef MBED_SSEL_SPI_H
+#define MBED_SSEL_SPI_H
+
+
+#include "mbed.h"
+extern "C" void TIMER2_IRQHandler (void);   //this method Linker loads ISR vector at compile time
+
+/**A hardware implimentation of a Serial (chip) SElect line output designed primarily for SPI (Serial Peripheral Interface)
+    *   devices by utilizing mbed LPC1768 Timer 2 hardware and it's inturrupt features.
+    *
+    *   Use of this class does require hardwiring p30 to the serial clock output (usually p7 or p13).
+    *
+    *   p8 is the SSEL serial select output pin (chip select) and is not relocatable.
+    *
+    *   Some SPI peripherals require data latching while the serial clock is still active on
+    *   the last bit clocked-in, such as the Maxim MAX6952. Using the mbed SPI and DigitalOut API's 
+    *   (for chip select) this timing is not possible. This SSEL_spi class takes advantage of 
+    *   the speed achievable with the mbed SPI API, and leaves the chip select output handling
+    *   entirely in the capable hands of the Timer 2 hardware with fully automated frame lengths 
+    *   making code simpler to write and read.
+    *
+    *       - Flexible serial frame lengths from 0 .. 4,294,967,295 bits (usually a multiple of SPI bit length)
+    *       - Un-attended automation of the chip select line.
+    *       - Selectable mode for proper clock polarity and edge trigger (make same as SPI mode).
+    *       - Selectable chip select polarity (active-low or active-high).
+    *       - Latching data in while clock is still active on last bit,
+    *         **such as required by the Maxim MAX6952. This is not possible with the mbed API, 
+    *         onboard SPI or SSP hardware alone. SPI speed is limited up to 3Mhz for this feature. 
+    *         Higher SPI speeds are permissable although due to the limitations of the hardware the chip 
+    *         select will latch AFTER sclk returns to the inactive state, tolerated by some serial peripherals.
+    *       - Allows one-shot loading of all serial daisy-chained hardware registers before latching. 
+    *         Prevents display ghosting effect. For example 
+    *         a daisy-chain of seven serial chips each requiring 16 bits each would set up a frame
+    *         length of 7 x 16 = 112 bit frame length.
+    * 
+    *   The MAX6952 chip requires the following sequence:
+    *
+    *       [[http://datasheets.maxim-ic.com/en/ds/MAX6952.pdf]]
+    *       -# Take CLK low.
+    *       -# Take CS low. This enables the internal 16-bit shift register.
+    *       -# Clock 16 bits of data into DIN, D15 first to D0 last, observing the setup and hold times. Bit D15 is low, indicating a write command.
+    *       -# Take CS high **(while CLK is still high after clocking in the last data bit).
+    *       -# Take CLK low.
+    *
+    * Example:
+    * @code
+    * // Send a 16 bit word to a SPI slave
+    * // NOTE:  You must hardwire sclk output pin (usually p7 or p13)
+    * //        to p30 which is the CAP2.0 sensing pin used by Timer2.
+    *  
+    * // Chip select is automatic and will always be p8
+    *
+    * #include "mbed.h"
+    * #include "SSEL_spi.h"
+    *
+    * SPI      spi(p5,p6,p7); //mosi, miso, sclk
+    * SSEL_spi cs(16,0);      //16 bits per frame, mode 0 (mode optional, 0 is default)
+    *
+    * int main(){
+    * cs.active(1);           //optionally will establish active-high (1) chip select
+    * spi.format(16,0);
+    * spi.frequency(1000000);
+    *
+    * while(1) spi.write(0x5555); 
+    *   
+    * }
+    * @endcode
+    */
+class SSEL_spi {    
+
+public:
+/**Create automatated SSEL chip select output for an SPI interface on p8 utilizing Timer2. Must hardwire SPI sclk output pin to p30.
+    *
+    *   @param frame Bit Length of the SSEL chip select frame. Usually a multiple of the SPI bit length transmission.
+    *   @param mode Set up proper triggering from SPI sclk output. Default mode = 0. Set mode same as SPI mode.
+    * 
+    */
+    SSEL_spi(uint32_t frame, int mode=0);
+
+/** Set active state of the chip select pin 8
+    *
+    *  Is active-low (0) by default. Call only if change needed.
+    *
+    *   Can also be called to force an output high or low condition.
+    *   @param cs 0 (default) for active-low, 1 for active-high
+    */
+    void active(bool cs);        
+protected:
+
+private:
+
+};
+#endif