FPC: got RX working, got client over usart somehow working..., see detailed commit msg

* using WITH_FPC:
  * activate basic usart
  * no double buffer for now, no interrupt
  * usart_dataavailable/usart_readbuffer/usart_writebuffer, to demo it:
    * pm3 client over USB, minicom over usart
    * analyse a d 414243
* using WITH_FPC_HOST:
  * it implies WITH_FPC as it's based on it
  * control pm3 with client over usart
  * EXPERIMENTAL! still some frame desync issues
  * you can connect both from usart & USB with two pm3 clients
    * actually you *have* to connect USB for the moment because
      it's used to send debug messages about buggy usart... See Dbprintf_usb below
  * "sessions": msgs are directed to the latest client to have sent a cmd
  * Dbprintf_usb macro to send msgs to USB client to help debugging usart...
  * We now have an option to run client at different speed as usart is 115200:
    client/proxmark3 /dev/ttyUSB0 -b 115200
  * Consequently, argc,argv handling is a bit revamped, it was so messy...
  * USB and flashing are still at 460800, don't try flashing over usart yet ^^

common/usart.c

@@ -10,6 +10,7 @@
 //-----------------------------------------------------------------------------
 #include "usart.h"
 #include "string.h"
+#include "apps.h"  // for Dbprintf
 
 #define AT91_BAUD_RATE 115200
 
@@ -39,52 +40,58 @@ void usart_close(void) {
 }
 */
 
+static uint8_t us_inbuf[sizeof(UsbCommand)];
 static uint8_t us_outbuf[sizeof(UsbCommand)];
 
-/// Reads data from an USART peripheral
-/// \param data  Pointer to the buffer where the received data will be stored.
-/// \param len  Size of the data buffer (in bytes).
-inline int16_t usart_readbuffer(uint8_t *data, size_t len) {
-
-    // Check if the first PDC bank is free
-    if (!(pUS1->US_RCR)) {
-        pUS1->US_RPR = (uint32_t)data;
-        pUS1->US_RCR = len;
-
-        pUS1->US_PTCR = AT91C_PDC_RXTEN | AT91C_PDC_TXTDIS;
-        return 2;
-    }
-    // Check if the second PDC bank is free
-    else if (!(pUS1->US_RNCR)) {
-        pUS1->US_RNPR = (uint32_t)data;
-        pUS1->US_RNCR = len;
-
-        pUS1->US_PTCR = AT91C_PDC_RXTEN | AT91C_PDC_TXTDIS;
-        return 1;
+// transfer from client to device
+inline int16_t usart_readbuffer(uint8_t *data) {
+    uint32_t rcr = pUS1->US_RCR;
+    if (rcr < sizeof(us_inbuf)) {
+        pUS1->US_PTCR = AT91C_PDC_RXTDIS;
+        memcpy(data, us_inbuf, sizeof(us_inbuf) - rcr);
+        // Reset DMA buffer
+        pUS1->US_RPR = (uint32_t)us_inbuf;
+        pUS1->US_RCR = sizeof(us_inbuf);
+        pUS1->US_PTCR = AT91C_PDC_RXTEN;
+        return sizeof(us_inbuf) - rcr;
     } else {
         return 0;
     }
 }
 
 inline bool usart_dataavailable(void) {
-    return (pUS1->US_CSR & AT91C_US_RXRDY) != 0;
+    return pUS1->US_RCR < sizeof(us_inbuf);
+}
+
+inline int16_t usart_readcommand(uint8_t *data) {
+    if (pUS1->US_RCR == 0)
+        return usart_readbuffer(data);
+    else
+        return 0;
+}
+
+inline bool usart_commandavailable(void) {
+    return pUS1->US_RCR == 0;
 }
 
 // transfer from device to client
 inline int16_t usart_writebuffer(uint8_t *data, size_t len) {
-    if (pUS1->US_TCR == 0) {
+
+
+    if (pUS1->US_CSR & AT91C_US_ENDTX) {
         memcpy(us_outbuf, data, len);
         pUS1->US_TPR = (uint32_t)us_outbuf;
         pUS1->US_TCR = len;
-
-        pUS1->US_PTCR = AT91C_PDC_TXTEN | AT91C_PDC_RXTDIS;
-        while((pUS1->US_CSR & AT91C_US_TXEMPTY) ==0) {};
-        return 2;
+        pUS1->US_PTCR = AT91C_PDC_TXTEN;
+        while(!(pUS1->US_CSR & AT91C_US_ENDTX)) {};
+        pUS1->US_PTCR = AT91C_PDC_TXTDIS;
+        return len;
     } else {
         return 0;
     }
 }
 
+
 void usart_init(void) {
 
     // For a nice detailed sample, interrupt driven but still relevant.
@@ -128,6 +135,17 @@ void usart_init(void) {
     pUS1->US_FIDI = 0;
     pUS1->US_IF = 0;
 
+    // Disable double buffers for now
+    pUS1->US_TNPR = (uint32_t)0;
+    pUS1->US_TNCR = 0;
+    pUS1->US_RNPR = (uint32_t)0;
+    pUS1->US_RNCR = 0;
+
+
     // re-enable receiver / transmitter
     pUS1->US_CR = (AT91C_US_RXEN | AT91C_US_TXEN);
+    // ready to receive
+    pUS1->US_RPR = (uint32_t)us_inbuf;
+    pUS1->US_RCR = sizeof(us_inbuf);
+    pUS1->US_PTCR = AT91C_PDC_RXTEN;
 }