From 8dec0d1be5a2d7633045c5c0e86b32a9e6b60299 Mon Sep 17 00:00:00 2001
From: Keith Packard <keithp@keithp.com>
Date: Mon, 17 May 2021 22:33:21 -0700
Subject: [PATCH] altos/telegps-*: Fix log end discovery at startup

We need to find the first unwritten log block to start appending data,
but the code was actually looking for the first empty 256-byte chunk,
which meant that we'd leave a gap of erased data after the previous
log. AltosUI would stop at that point and not recover the remaining
stored data.

Signed-off-by: Keith Packard <keithp@keithp.com>
---
 src/kernel/ao_log_gps.c | 19 ++++++++++++++++---
 src/kernel/ao_storage.c |  4 ----
 src/kernel/ao_storage.h |  4 ++++
 3 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/src/kernel/ao_log_gps.c b/src/kernel/ao_log_gps.c
index bf326c1a..2b45f35e 100644
--- a/src/kernel/ao_log_gps.c
+++ b/src/kernel/ao_log_gps.c
@@ -81,18 +81,31 @@ ao_log_gps_tracking(uint16_t tick, struct ao_telemetry_satellite *gps_tracking_d
 	ao_log_write(&ao_log_data);
 }
 
+static uint8_t
+ao_log_check_empty(void)
+{
+	uint8_t *b = (void *) &ao_log_data;
+	unsigned i;
+
+	for (i = 0; i < sizeof (ao_log_type); i++)
+		if (*b++ != AO_STORAGE_ERASED_BYTE)
+			return 0;
+	return 1;
+}
+
 int8_t
 ao_log_check(uint32_t pos)
 {
-	if (ao_storage_is_erased(pos & ~(ao_storage_block - 1)))
-		return 0;
-
 	if (!ao_storage_read(pos,
 			     &ao_log_data,
 			     sizeof (struct ao_log_gps)))
 		return AO_LOG_INVALID;
 
+	if (ao_log_check_empty())
+		return AO_LOG_EMPTY;
+
 	if (!ao_log_check_data())
 		return AO_LOG_INVALID;
+
 	return AO_LOG_VALID;
 }
diff --git a/src/kernel/ao_storage.c b/src/kernel/ao_storage.c
index 213ec2d6..43abc43c 100644
--- a/src/kernel/ao_storage.c
+++ b/src/kernel/ao_storage.c
@@ -86,10 +86,6 @@ ao_storage_write(ao_pos_t pos, void *v_buf, uint16_t len)
 	return 1;
 }
 
-#ifndef AO_STORAGE_ERASED_BYTE
-#define AO_STORAGE_ERASED_BYTE 0xff
-#endif
-
 uint8_t
 ao_storage_is_erased(uint32_t pos)
 {
diff --git a/src/kernel/ao_storage.h b/src/kernel/ao_storage.h
index 026074b5..ff8548eb 100644
--- a/src/kernel/ao_storage.h
+++ b/src/kernel/ao_storage.h
@@ -44,6 +44,10 @@ extern ao_pos_t	ao_storage_block;
 #define USE_STORAGE_CONFIG 1
 #endif
 
+#ifndef AO_STORAGE_ERASED_BYTE
+#define AO_STORAGE_ERASED_BYTE 0xff
+#endif
+
 #if USE_STORAGE_CONFIG
 /* Byte offset of config block. Will be ao_storage_block bytes long */
 extern ao_pos_t	ao_storage_config;
-- 
2.30.2