2 files changed, 91 insertions, 0 deletions
diff --git a/stm32f091/backlog.c b/stm32f091/backlog.c
new file mode 100644
index 0000000..3f21924
--- /dev/null
+++ b/stm32f091/backlog.c
@@ -0,0 +1,34 @@
+#include <stdlib.h>
+
+#include "backlog.h"
+
+ws_s_backlog_database* WS_G_BACKLOG_DATABASE = NULL;
+
+void ws_backlog_alloc(uint16_t record_amt) {
+	WS_G_BACKLOG_DATABASE = malloc(sizeof(ws_s_backlog_database) + sizeof(ws_s_backlog_record) * record_amt);
+	WS_G_BACKLOG_DATABASE->buffer_size = record_amt;
+	WS_G_BACKLOG_DATABASE->buffer_start = 0;
+	WS_G_BACKLOG_DATABASE->buffer_end = 0;
+}
+
+void ws_backlog_add_record(ws_s_backlog_record record) {
+	static uint16_t id = 0;
+
+	WS_G_BACKLOG_DATABASE->records[WS_G_BACKLOG_DATABASE->buffer_end].id = id++;
+	WS_G_BACKLOG_DATABASE->records[WS_G_BACKLOG_DATABASE->buffer_end].sens_atm_pressure = record.sens_atm_pressure;
+	WS_G_BACKLOG_DATABASE->records[WS_G_BACKLOG_DATABASE->buffer_end].sens_humidity = record.sens_humidity;
+	WS_G_BACKLOG_DATABASE->records[WS_G_BACKLOG_DATABASE->buffer_end].sens_temperature = record.sens_temperature;
+
+	// shift buffer start/end
+	WS_G_BACKLOG_DATABASE->buffer_end = (WS_G_BACKLOG_DATABASE->buffer_end + 1) % WS_G_BACKLOG_DATABASE->buffer_size;
+	if (WS_G_BACKLOG_DATABASE->buffer_end == WS_G_BACKLOG_DATABASE->buffer_start)
+		WS_G_BACKLOG_DATABASE->buffer_start = (WS_G_BACKLOG_DATABASE->buffer_start + 1) % WS_G_BACKLOG_DATABASE->buffer_size;
+}
+
+ws_s_backlog_record* ws_backlog_get_record(uint16_t record_index) {
+	return &WS_G_BACKLOG_DATABASE->records[record_index];
+}
+
+ws_s_backlog_record* ws_backlog_get_last_record(uint16_t record_offset) {
+	return ws_backlog_get_record((WS_G_BACKLOG_DATABASE->buffer_end - record_offset - 1) % WS_G_BACKLOG_DATABASE->buffer_size);
+}
diff --git a/stm32f091/backlog.h b/stm32f091/backlog.h
new file mode 100644
index 0000000..465b3c0
--- /dev/null
+++ b/stm32f091/backlog.h
@@ -0,0 +1,57 @@
+#pragma once
+
+#include <stdint.h>
+
+/**
+ * @brief allocate backlog buffer and set global backlog pointer
+ * @param record_amt amount of records to keep before overwriting oldest record
+ */
+void ws_backlog_alloc(uint16_t record_amt);
+
+// enable struct packing
+#pragma pack(push, 1)
+
+/** @brief backlog record */
+typedef struct {
+	uint16_t id; /**< unique record identifier, numbered sequentially */
+	uint8_t sens_temperature; /**< temperature reading */
+	uint8_t sens_humidity; /**< humidity reading */
+	uint8_t sens_atm_pressure; /**< atmospheric pressure reading */
+} ws_s_backlog_record;
+
+typedef struct {
+	uint16_t buffer_size; /**< buffer size (amount of records) */
+	uint16_t buffer_start; /** first record index */
+	uint16_t buffer_end; /** last record index */
+	ws_s_backlog_record records[]; /** record array */
+} ws_s_backlog_database;
+
+// disable struct packing
+#pragma pack(pop)
+
+/** @brief global record backlog database pointer */
+extern ws_s_backlog_database* WS_G_BACKLOG_DATABASE;
+
+/**
+ * @brief add record to database
+ *
+ * automatically sets record.id, pushes buffer_end forwards and overwrites the
+ * last record if the buffer is full
+ */
+void ws_backlog_add_record(ws_s_backlog_record record);
+
+/**
+ * there's intentionally no function to retrieve multiple records as an array,
+ * as this would either require
+ * (a) copying the selection which is not possible with the current memory
+ * constraints, or
+ * (b) giving a direct pointer, but this would cause undefined behavior at the
+ * ring buffer seam
+ */
+
+/** @brief get pointer to record with index `record_index` from the database */
+ws_s_backlog_record* ws_backlog_get_record(uint16_t record_index);
+
+/** @brief get pointer to last record with offset `record_offset` from the database */
+ws_s_backlog_record* ws_backlog_get_last_record(uint16_t record_offset);
+