From 0b95c519ff4a034dba64a8340cb63a08dcc39f38 Mon Sep 17 00:00:00 2001
From: merlokk <807634+merlokk@users.noreply.github.com>
Date: Sat, 9 Jul 2022 16:45:08 +0300
Subject: [PATCH] sh sniff skip some bytes from data - arm side

---
 armsrc/appmain.c |  4 +++-
 armsrc/hfsnoop.c | 46 ++++++++++++++++++++++++++++++++++++++++++++--
 armsrc/hfsnoop.h |  9 ++++++++-
 3 files changed, 55 insertions(+), 4 deletions(-)

diff --git a/armsrc/appmain.c b/armsrc/appmain.c
index 106fe3903..330bf2c48 100644
--- a/armsrc/appmain.c
+++ b/armsrc/appmain.c
@@ -1784,11 +1784,13 @@ static void PacketReceived(PacketCommandNG *packet) {
             struct p {
                 uint32_t samplesToSkip;
                 uint32_t triggersToSkip;
+                uint8_t skipMode;
+                uint8_t skipRatio;
             } PACKED;
             struct p *payload = (struct p *)packet->data.asBytes;
 
             uint16_t len = 0;
-            int res = HfSniff(payload->samplesToSkip, payload->triggersToSkip, &len);
+            int res = HfSniff(payload->samplesToSkip, payload->triggersToSkip, &len, payload->skipMode, payload->skipRatio);
 
             struct {
                 uint16_t len;
diff --git a/armsrc/hfsnoop.c b/armsrc/hfsnoop.c
index ba9ef0740..f12b4863b 100644
--- a/armsrc/hfsnoop.c
+++ b/armsrc/hfsnoop.c
@@ -36,7 +36,46 @@ static void RAMFUNC optimizedSniff(uint16_t *dest, uint16_t dsize) {
     }
 }
 
-int HfSniff(uint32_t samplesToSkip, uint32_t triggersToSkip, uint16_t *len) {
+static void RAMFUNC skipSniff(uint8_t *dest, uint16_t dsize, uint8_t skipMode, uint8_t skipRatio) {
+    uint32_t accum = (skipMode == HF_SNOOP_SKIP_MIN) ? 0xffffffff : 0;
+    uint8_t ratioindx = 0;
+    while (dsize > 0) {
+        if (AT91C_BASE_SSC->SSC_SR & AT91C_SSC_RXRDY) {
+            volatile uint16_t val = (uint16_t)(AT91C_BASE_SSC->SSC_RHR);
+            switch (skipMode) {
+                case HF_SNOOP_SKIP_MAX:
+                    if (accum < (val & 0xff))
+                        accum = val & 0xff;
+                    if (accum < (val << 8))
+                        accum = val << 8;
+                case HF_SNOOP_SKIP_MIN:
+                    if (accum > (val & 0xff))
+                        accum = val & 0xff;
+                    if (accum > (val << 8))
+                        accum = val << 8;
+                case HF_SNOOP_SKIP_AVG:
+                        accum += (val & 0xff) + (val << 8);
+                default: { // HF_SNOOP_SKIP_DROP and the rest 
+                    if (ratioindx == 0)
+                        accum = val & 0xff;
+                }
+            }
+
+            ratioindx++;
+            if (ratioindx >= skipRatio) {
+                ratioindx = 0;
+                if (skipMode == HF_SNOOP_SKIP_AVG)
+                    *dest = accum / (skipRatio * 2);
+                else
+                    *dest = accum;
+                dest++;
+                dsize --;
+            }
+        }
+    }
+}
+
+int HfSniff(uint32_t samplesToSkip, uint32_t triggersToSkip, uint16_t *len, uint8_t skipMode, uint8_t skipRatio) {
     BigBuf_free();
     BigBuf_Clear_ext(false);
 
@@ -105,7 +144,10 @@ int HfSniff(uint32_t samplesToSkip, uint32_t triggersToSkip, uint16_t *len) {
             }
         }
 
-        optimizedSniff((uint16_t *)mem, *len);
+        if (skipMode == 0)
+            optimizedSniff((uint16_t *)mem, *len);
+        else
+            skipSniff(mem, *len, skipMode, skipRatio);
 
         if (g_dbglevel >= DBG_INFO) {
             Dbprintf("Trigger kicked in (%d >= 180)", r);
diff --git a/armsrc/hfsnoop.h b/armsrc/hfsnoop.h
index 4b715753d..a68d28a79 100644
--- a/armsrc/hfsnoop.h
+++ b/armsrc/hfsnoop.h
@@ -18,6 +18,13 @@
 
 #include "proxmark3_arm.h"
 
-int HfSniff(uint32_t samplesToSkip, uint32_t triggersToSkip, uint16_t *len);
+// what to do with skipped data
+#define HF_SNOOP_SKIP_NONE (0)
+#define HF_SNOOP_SKIP_DROP (1)
+#define HF_SNOOP_SKIP_MAX  (2)
+#define HF_SNOOP_SKIP_MIN  (3)
+#define HF_SNOOP_SKIP_AVG  (4)
+
+int HfSniff(uint32_t samplesToSkip, uint32_t triggersToSkip, uint16_t *len, uint8_t skipMode, uint8_t skipRatio);
 void HfPlotDownload(void);
 #endif