Diff: example_dma.cpp

Revision:

9:b3cdae80e7a9

Child:

11:a93a62eeeb9d

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/example_dma.cpp	Tue Nov 23 21:34:54 2010 +0000
@@ -0,0 +1,144 @@
+#ifdef COMPILE_EXAMPLE_CODE_MODSERIAL_MODDMA
+
+/*
+ * To run this test program, link p9 to p10 so the Serial loops
+ * back and receives characters it sends.
+ */
+ 
+#include "mbed.h"
+
+/* Note, this example requires that you also import into the Mbed
+   compiler the MODDMA project as well as MODSERIAL
+   http://mbed.org/users/AjK/libraries/MODDMA/latest 
+   MODDMA.h MUST come before MODSERIAL.h */
+#include "MODDMA.h"     // <--- Declare first
+#include "MODSERIAL.h"  // Flollowed by MODSERIAL
+
+DigitalOut led1(LED1);
+DigitalOut led2(LED2);
+DigitalOut led3(LED3);
+DigitalOut led4(LED4);
+
+MODSERIAL pc(USBTX, USBRX);
+
+/*
+ * As experiement, you can define MODSERIAL as show here and see what
+ * effects it has on the LEDs.
+ *
+ * MODSERIAL uart(TX_PIN, RX_PIN, 512);
+ *   With this, the 512 characters sent can straight into the buffer
+ *   vary quickly. This means LED1 is only on briefly as the TX buffer
+ *   fills.
+ *
+ * MODSERIAL uart(TX_PIN, RX_PIN, 32);
+ *   With this, the buffer is smaller than the default 256 bytes and
+ *   therefore LED1 stays on much longer while the system waits for
+ *   room in the TX buffer.
+ */
+MODSERIAL uart(TX_PIN, RX_PIN);
+
+MODDMA dma;
+
+// This function is called when a character goes from the TX buffer
+// to the Uart THR FIFO register.
+void txCallback(void) {
+    led2 = !led2;
+}
+
+// This function is called when TX buffer goes empty
+void txEmpty(void) {
+    led2 = 0;
+    pc.puts(" Done. ");
+}
+
+void dmaComplete(void) {
+    led1 = 1;
+}
+
+// This function is called when a character goes into the RX buffer.
+void rxCallback(void) {
+    led3 = !led3;
+    pc.putc(uart.getc());
+}
+
+int main() {
+    char s1[] = " *DMA* *DMA* *DMA* *DMA* *DMA* *DMA* *DMA* ";
+    int c = 'A';
+    
+    // Tell MODSERIAL where the MODDMA controller is.
+    pc.MODDMA( &dma );
+    
+    // Ensure the baud rate for the PC "USB" serial is much
+    // higher than "uart" baud rate below.
+    pc.baud( PC_BAUD );
+    
+    // Use a deliberatly slow baud to fill up the TX buffer
+    uart.baud(1200);
+    
+    uart.attach( &txCallback, MODSERIAL::TxIrq );
+    uart.attach( &rxCallback, MODSERIAL::RxIrq );
+    uart.attach( &txEmpty,    MODSERIAL::TxEmpty );
+    
+    // Loop sending characters. We send 512
+    // which is twice the default TX/RX buffer size.
+    
+    led1 = 0;
+    
+    // Send the buffer s using DMA channel 7
+    pc.attach_dma_complete( &dmaComplete );
+    pc.dmaSend( s1, sizeof(s1), MODDMA::Channel_7 );
+    
+    for (int loop = 0; loop < 512; loop++) {
+        uart.printf("%c", c);        
+        c++;
+        if (c > 'Z') c = 'A';
+    }
+    
+    led1 = 0; // Show the end of sending by switching off LED1.
+    
+    // End program. Flash LED4. Notice how LED 2 and 3 continue
+    // to flash for a short period while the interrupt system 
+    // continues to send the characters left in the TX buffer.
+    
+    while(1) {
+        led4 = !led4;
+        wait(0.25);
+    }
+}
+
+/*
+ * Notes. Here is the sort of output you can expect on your PC/Mac/Linux host
+ * machine that is connected to the "pc" USB serial port.
+ *
+ *  *DMA* *DMA* *DMA* *DMA* *DMA* *DMA* *DMA* ABCDEFGHIJKLMNOPQRSTUVWXYZABCDE
+ * FGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZA
+ * BCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVW
+ * XYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRS
+ * TUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNO
+ * PQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJK
+ * LMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFG
+ * HIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQ Done. R
+ *
+ * Note how the DMA blocks the TX buffer sending under standard interrupt control.
+ * Not until the DMA transfer is complete will "normal" buffered TX sending resume.
+ *
+ * Of interest is that last "R" character after the system has said "Done."
+ * This comes from the fact that the TxEmpty callback is made when the TX buffer
+ * becomes empty. MODSERIAL makes use of the fact that the Uarts built into the 
+ * LPC17xx device use a 16 byte FIFO on both RX and TX channels. This means that
+ * when the TxEmpty callback is made, the TX buffer is empty, but that just means
+ * the "last few characters" were written to the TX FIFO. So although the TX
+ * buffer has gone empty, the Uart's transmit system is still sending any remaining
+ * characters from it's TX FIFO. If you want to be truely sure all the characters
+ * you have sent have left the Mbed then call txIsBusy(); This function will
+ * return true if characters are still being sent. If it returns false after
+ * the Tx buffer is empty then all your characters have been sent.
+ *
+ * In a similar way, when characters are received into the RX FIFO, the entire
+ * FIFO contents is moved to the RX buffer, assuming there is room left in the
+ * RX buffer. If there is not, any remaining characters are left in the RX FIFO
+ * and will be moved to the RX buffer on the next interrupt or when the running 
+ * program removes a character(s) from the RX buffer with the getc() method.
+ */
+ 
+#endif