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Improve CDC read code #1953

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66 changes: 12 additions & 54 deletions hardware/arduino/cores/arduino/CDC.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -23,21 +23,6 @@
#if defined(USBCON)
#ifdef CDC_ENABLED

#if (RAMEND < 1000)
#define SERIAL_BUFFER_SIZE 16
#else
#define SERIAL_BUFFER_SIZE 64
#endif

struct ring_buffer
{
unsigned char buffer[SERIAL_BUFFER_SIZE];
volatile int head;
volatile int tail;
};

ring_buffer cdc_rx_buffer = { { 0 }, 0, 0};

typedef struct
{
u32 dwDTERate;
Expand Down Expand Up @@ -129,7 +114,6 @@ bool WEAK CDC_Setup(Setup& setup)
}


int _serialPeek = -1;
void Serial_::begin(unsigned long baud_count)
{
}
Expand All @@ -142,55 +126,29 @@ void Serial_::end(void)
{
}

void Serial_::accept(void)
{
ring_buffer *buffer = &cdc_rx_buffer;
int i = (unsigned int)(buffer->head+1) % SERIAL_BUFFER_SIZE;

// if we should be storing the received character into the location
// just before the tail (meaning that the head would advance to the
// current location of the tail), we're about to overflow the buffer
// and so we don't write the character or advance the head.

// while we have room to store a byte
while (i != buffer->tail) {
int c = USB_Recv(CDC_RX);
if (c == -1)
break; // no more data
buffer->buffer[buffer->head] = c;
buffer->head = i;

i = (unsigned int)(buffer->head+1) % SERIAL_BUFFER_SIZE;
}
}

int Serial_::available(void)
{
ring_buffer *buffer = &cdc_rx_buffer;
return (unsigned int)(SERIAL_BUFFER_SIZE + buffer->head - buffer->tail) % SERIAL_BUFFER_SIZE;
if (peek_buffer >= 0) {
return 1;
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I guess that the
return 1;
should be:
return 1 + USB_Available(CDC_RX);

To avoid situations where queued chars may seems to "disappear":

av1 = Serial.available(); // av1 may be > 1
Serial.peek();
av2 = Serial.available(); // after the peek av2 is 1

assert(av2>=av1); // Assertion fails if av1>1

}
return USB_Available(CDC_RX);
}

int Serial_::peek(void)
{
ring_buffer *buffer = &cdc_rx_buffer;
if (buffer->head == buffer->tail) {
return -1;
} else {
return buffer->buffer[buffer->tail];
}
if (peek_buffer < 0)
peek_buffer = USB_Recv(CDC_RX);
return peek_buffer;
}

int Serial_::read(void)
{
ring_buffer *buffer = &cdc_rx_buffer;
// if the head isn't ahead of the tail, we don't have any characters
if (buffer->head == buffer->tail) {
return -1;
} else {
unsigned char c = buffer->buffer[buffer->tail];
buffer->tail = (unsigned int)(buffer->tail + 1) % SERIAL_BUFFER_SIZE;
if (peek_buffer >= 0) {
int c = peek_buffer;
peek_buffer = -1;
return c;
}
}
return USB_Recv(CDC_RX);
}

void Serial_::flush(void)
Expand Down
3 changes: 1 addition & 2 deletions hardware/arduino/cores/arduino/USBAPI.h
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Original file line number Diff line number Diff line change
Expand Up @@ -28,14 +28,13 @@ extern USBDevice_ USBDevice;
class Serial_ : public Stream
{
private:
ring_buffer *_cdc_rx_buffer;
int peek_buffer;
public:
void begin(unsigned long);
void begin(unsigned long, uint8_t);
void end(void);

virtual int available(void);
virtual void accept(void);
virtual int peek(void);
virtual int read(void);
virtual void flush(void);
Expand Down
2 changes: 0 additions & 2 deletions hardware/arduino/cores/arduino/USBCore.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -611,8 +611,6 @@ ISR(USB_GEN_vect)
{
#ifdef CDC_ENABLED
USB_Flush(CDC_TX); // Send a tx frame if found
if (USB_Available(CDC_RX)) // Handle received bytes (if any)
Serial.accept();
#endif

// check whether the one-shot period has elapsed. if so, turn off the LED
Expand Down