From 601559ca6e14723466152cd61f0abf4fbbb1de2c Mon Sep 17 00:00:00 2001
From: Martin Preuss <martin@aquamaniac.de>
Date: Sun, 9 Feb 2025 21:05:48 +0100
Subject: [PATCH] avr: added RingBufferY_PeekByte

---
 avr/common/m_ringbuffer_y.asm | 37 +++++++++++++++++++++++++++++++++++
 avr/common/ringbuffer_y.asm   | 29 +++++++++++++++++++++++++--
 2 files changed, 64 insertions(+), 2 deletions(-)

diff --git a/avr/common/m_ringbuffer_y.asm b/avr/common/m_ringbuffer_y.asm
index 7a8fa1d..31ca3c3 100644
--- a/avr/common/m_ringbuffer_y.asm
+++ b/avr/common/m_ringbuffer_y.asm
@@ -92,6 +92,43 @@ l_end:
 
 
 
+; ---------------------------------------------------------------------------
+; @macro m_ringbuffer_y_peekbyte
+;
+; @param Y   base address (for "LDD Y+nn" and "STD Y+nn")
+; @param %0 offset to Y to access maxBytes variable (for "LDD Y+nn" and "STD Y+nn")
+; @param %1 offset to Y to access usedBytes
+; @param %2 offset to Y to access readPos variable
+; @param %3 offset to Y to access writePos variable
+; @param %4 offset to Y to access buffer
+; @return CFLAG set if okay, cleared on error (i.e. buffer full)
+; @return R16 byte read
+; @clobbers R17, R18, X
+
+.macro m_ringbuffer_y_peekbyte
+  ldd r18, Y+@0 ; maxBytes
+  ldd r17, Y+@1 ; usedBytes
+  tst r17
+  clc
+  breq l_end
+  dec r17
+  std Y+@1, r17 ; usedBytes
+  ldd r17, Y+@2 ; readPos
+  mov xl, yl
+  mov xh, yh
+  adiw xh:xl, @4
+  add xl, r17
+  adc xh, r17
+  sub xh, r17
+  ld r16, X
+  std Y+@2, r17 ; readPos
+  sec
+l_end:
+.endmacro
+; @end
+
+
+
 ; ---------------------------------------------------------------------------
 ; @macro m_ringbuffer_y_reset
 ;
diff --git a/avr/common/ringbuffer_y.asm b/avr/common/ringbuffer_y.asm
index ac56ddc..76c618d 100644
--- a/avr/common/ringbuffer_y.asm
+++ b/avr/common/ringbuffer_y.asm
@@ -52,9 +52,9 @@ RingBufferY_WriteByte:
 
 
 ; ---------------------------------------------------------------------------
-; @macro m_ringbuffer_y_readbyte
+; @routine RingBufferY_ReadByte
 ;
-; @param Y   base address of ringbuffer struct
+; @param  Y     base address of ringbuffer struct
 ; @return CFLAG set if okay, cleared on error (i.e. buffer empty)
 ; @return R16 byte read
 ; @clobbers R17, R18, X
@@ -71,6 +71,31 @@ RingBufferY_ReadByte:
 
 
 
+; ---------------------------------------------------------------------------
+; @routine RingBufferY_PeekByte
+;
+; @param Y   base address (for "LDD Y+nn" and "STD Y+nn")
+; @param %0 offset to Y to access maxBytes variable (for "LDD Y+nn" and "STD Y+nn")
+; @param %1 offset to Y to access usedBytes
+; @param %2 offset to Y to access readPos variable
+; @param %3 offset to Y to access writePos variable
+; @param %4 offset to Y to access buffer
+; @return CFLAG set if okay, cleared on error (i.e. buffer empty)
+; @return R16 byte read
+; @clobbers R17, R18, X
+
+RingBufferY_PeekByte:
+  m_ringbuffer_y_peekbyte \
+    RINGBUFFERY_OFFS_MAXSIZE, \
+    RINGBUFFERY_OFFS_USED, \
+    RINGBUFFERY_OFFS_READPOS, \
+    RINGBUFFERY_OFFS_WRITEPOS, \
+    RINGBUFFERY_OFFS_DATA
+  ret
+; @end
+
+
+
 ; ---------------------------------------------------------------------------
 ; @macro m_ringbuffer_y_reset
 ;