backend: Export/import the Backend config as JSON

Add a new helper BackEnd::GetJsonConfig() to return a JSON string of
the current Backend register configuration and tile data. The parameters
are the actual register values to be programmed into the hardware, and
currently all dumped as unsigned.

Add a check for the environment variable LIBPISP_CONFIG_DUMP, and if if
it is set, use the filename provided to dump the config/tile JSON output
as a one-shot operation.

Add a new helper BackEnd::SetJsonConfig() to read a JSON string and
import the Backend register configuration. Tile data does not get
imported, and will need a BackEnd::Prepare() call to re-generate the
tile data.

Signed-off-by: Naushir Patuck <[email protected]>

src/libpisp/backend/backend.hpp

@@ -8,6 +8,7 @@
 #pragma once
 
 #include <map>
+#include <string>
 #include <vector>
 
 #include "common/shm_mutex.hpp"
@@ -130,6 +131,9 @@ class BackEnd
 
 	unsigned int GetMaxDownscale() const;
 
+	std::string GetJsonConfig(pisp_be_tiles_config *config);
+	void SetJsonConfig(const std::string &json_config);
+
 	void lock()
 	{
 		mutex_.lock();
@@ -175,6 +179,7 @@ class BackEnd
 	std::vector<std::pair<double, std::string>> resample_select_list_;
 	pisp_be_sharpen_config default_sharpen_;
 	pisp_be_sh_fc_combine_config default_shfc_;
+	std::string last_dump_file_;
 };
 
 } // namespace libpisp