Investigate whether TX and RX PDU sizes need to be different about cf

[skliper]

TX and RX PDU sizes can be different. Transmit maximum size is configurable via table using outgoing_file_chunk_size as defined below. Note the actual TX PDU also includes the PDU header which is variable size. The CCSDS header also needs to be accounted for to get to the final size over the SB.

CF/config/default_cf_tblstruct.h

Lines 51 to 52 in 27dcaf5

	uint16 outgoing_file_chunk_size; /**< maximum size of outgoing file data PDUs - must be
	* smaller than file data character array */

CF_MAX_PDU_SIZE is defined in the interface header here, note this includes the PDU headers but not the CCSDS header:

CF/config/default_cf_interface_cfg.h

Lines 94 to 95 in 27dcaf5

	/* CF_MAX_PDU_SIZE must be the max possible PDU for any channel. Channels can be configured with a smaller max. */
	#define CF_MAX_PDU_SIZE (512)

The outgoing_file_chunk_size is limited by this structure size:

CF/fsw/src/cf_cfdp_pdu.h

Lines 371 to 381 in 27dcaf5

	/**
	* @brief PDU file data content
	*
	* To serve as a sanity check, this should accommodate the largest data block possible.
	* In that light, it should be sized based on the minimum encoded header size, rather than
	* the maximum, as that case leaves the most space for data.
	*/
	typedef struct CF_CFDP_PduFileDataContent
	{
	uint8 data[CF_MAX_PDU_SIZE - sizeof(CF_CFDP_PduFileDataHeader_t) - CF_CFDP_MIN_HEADER_SIZE];
	} CF_CFDP_PduFileDataContent_t;

Note the comment below is actually misleading, since CF gets a buffer from SB and writes from the file to it directly:

CF/docs/dox_src/cfs_cf.dox

Lines 460 to 462 in 27dcaf5

	For outgoing file transactions, the engine uses a statically allocated buffer for
	PDUs. The size of this buffer is defined by platform configuration parameter,
	CF_MAX_PDU_SIZE. The engine informs the CF app when it has a PDU

On the receive side the PDU is processed "in place", so it isn't restricted by local CF buffer sizes. There's a misleading comment here:

CF/docs/dox_src/cfs_cf.dox

Lines 455 to 458 in 27dcaf5

	For incoming file transactions, CF uses a statically allocated buffer for the
	incoming PDU. The size of this buffer is defined by the platform configuration
	parameter, CF_MAX_PDU_SIZE. The incoming PDU's are copied from the Software Bus
	into this buffer and then passed to the engine.

Note that there is a structure defined below, but it's only used for size checking of outgoing_file_chunk_size and not directly:

CF/fsw/src/cf_cfdp_pdu.h

Lines 371 to 381 in 27dcaf5

	/**
	* @brief PDU file data content
	*
	* To serve as a sanity check, this should accommodate the largest data block possible.
	* In that light, it should be sized based on the minimum encoded header size, rather than
	* the maximum, as that case leaves the most space for data.
	*/
	typedef struct CF_CFDP_PduFileDataContent
	{
	uint8 data[CF_MAX_PDU_SIZE - sizeof(CF_CFDP_PduFileDataHeader_t) - CF_CFDP_MIN_HEADER_SIZE];
	} CF_CFDP_PduFileDataContent_t;

This comment is also wrong, since outgoing_file_chunk_size is common across channels:

CF/config/default_cf_interface_cfg.h

Lines 87 to 89 in 27dcaf5

	* the PDU headers and everything. While this is the max value for all
	* channels, the outgoing_file_chunk_size in the configuration table
	* is different for each channel so a smaller size can be used.

Also no longer applicable:

CF/fsw/src/cf_cfdp_types.h

Lines 413 to 415 in 27dcaf5

	/* NOTE: the use of CF_CFDP_PduHeader_t below is correct, but the CF_PduRecvMsg_t and CF_PduSendMsg_t
	* structures are both longer than these definitions. They are always backed by a buffer
	* of size CF_MAX_PDU_SIZE */