ringbuffer: Don't print/TRAC from ringbuffer

In commit eac1bec4285a48b466e9fd09b0513b3c49d393b3 we start to use the
ringbuffer inside the console printing code.  As a result, we must not
use TRACE_*() or printf() from within ringbuffer.c code to avoid
infinite recursion.

Instead, let rbuf_write() return a negative return value in case the
ring buffer overflows.  This way, the callers (outside the
console/stdout code) can print an error message themselves.

Change-Id: Ib009f013be119dbad22fa2b7d60ec8dee59baee5

3 files changed, 10 insertions, 4 deletions

diff --git a/firmware/libcommon/include/ringbuffer.h b/firmware/libcommon/include/ringbuffer.h
index 1d29760..efc557c 100644
--- a/firmware/libcommon/include/ringbuffer.h
+++ b/firmware/libcommon/include/ringbuffer.h
@@ -16,7 +16,7 @@ typedef struct ringbuf {
 void rbuf_reset(volatile ringbuf * rb);
 uint8_t rbuf_read(volatile ringbuf * rb);
 uint8_t rbuf_peek(volatile ringbuf * rb);
-void rbuf_write(volatile ringbuf * rb, uint8_t item);
+int rbuf_write(volatile ringbuf * rb, uint8_t item);
 bool rbuf_is_empty(volatile ringbuf * rb);
 bool rbuf_is_full(volatile ringbuf * rb);
 
diff --git a/firmware/libcommon/source/mode_cardemu.c b/firmware/libcommon/source/mode_cardemu.c
index 7de67df..2d9af99 100644
--- a/firmware/libcommon/source/mode_cardemu.c
+++ b/firmware/libcommon/source/mode_cardemu.c
@@ -186,7 +186,8 @@ static void usart_irq_rx(uint8_t inst_num)
 
 	if (csr & US_CSR_RXRDY) {
         	byte = (usart->US_RHR) & 0xFF;
-		rbuf_write(&ci->rb, byte);
+		if (rbuf_write(&ci->rb, byte) < 0)
+			TRACE_ERROR("rbuf overrun\r\n");
 	}
 
 	if (csr & US_CSR_TXRDY) {
diff --git a/firmware/libcommon/source/ringbuffer.c b/firmware/libcommon/source/ringbuffer.c
index 4d980d7..b8cd5c6 100644
--- a/firmware/libcommon/source/ringbuffer.c
+++ b/firmware/libcommon/source/ringbuffer.c
@@ -2,6 +2,10 @@
 #include "trace.h"
 #include "utils.h"
 
+/* WARNINGI: Since console output is internally using this ringbuffer to implement
+ * buffered writes, we cannot use any TRACE_*() or printf() style functions here,
+ * as it would create infinite recursion! */
+
 void rbuf_reset(volatile ringbuf * rb)
 {
 	unsigned long state;
@@ -52,7 +56,7 @@ bool rbuf_is_full(volatile ringbuf * rb)
 	return rc;
 }
 
-void rbuf_write(volatile ringbuf * rb, uint8_t item)
+int rbuf_write(volatile ringbuf * rb, uint8_t item)
 {
 	unsigned long state;
 
@@ -61,9 +65,10 @@ void rbuf_write(volatile ringbuf * rb, uint8_t item)
 		rb->buf[rb->iwr] = item;
 		rb->iwr = (rb->iwr + 1) % RING_BUFLEN;
 		local_irq_restore(state);
+		return 0;
 	} else {
 		local_irq_restore(state);
-		TRACE_ERROR("Ringbuffer full, losing bytes!");
+		return -1;
 	}
 }