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Improve header definitions #58

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6 changes: 3 additions & 3 deletions target/min.c
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,7 @@

// Number of bytes needed for a frame with a given payload length, excluding stuff bytes
// 3 header bytes, ID/control byte, length byte, seq byte, 4 byte CRC, EOF byte
#define ON_WIRE_SIZE(p) ((p) + 11U)
#define ON_WIRE_SIZE(p) ((p) + MIN_OVERHEAD)

// Special protocol bytes
enum {
Expand Down Expand Up @@ -504,11 +504,11 @@ static void rx_byte(struct min_context *self, uint8_t byte)
crc32_step(&self->rx_checksum, byte);
if (self->rx_frame_length > 0) {
// Can reduce the RAM size by compiling limits to frame sizes
if (self->rx_frame_length <= MAX_PAYLOAD) {
if (self->rx_frame_length <= MIN_MAX_PAYLOAD) {
self->rx_frame_state = RECEIVING_PAYLOAD;
} else {
// Frame dropped because it's longer than any frame we can buffer
min_debug_print("Dropping frame because length %d > MAX_PAYLOAD %d", self->rx_frame_length, MAX_PAYLOAD);
min_debug_print("Dropping frame because length %d > MIN_MAX_PAYLOAD %d", self->rx_frame_length, MIN_MAX_PAYLOAD);
self->rx_frame_state = SEARCHING_FOR_SOF;
}
} else {
Expand Down
33 changes: 26 additions & 7 deletions target/min.h
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Original file line number Diff line number Diff line change
Expand Up @@ -70,8 +70,31 @@
#define TRANSPORT_PROTOCOL
#endif

#ifndef MAX_PAYLOAD
#define MAX_PAYLOAD (255U)
// Number of bytes needed for a frame with a given payload length, excluding stuff bytes
// 3 header bytes, ID/control byte, length byte, seq byte, 4 byte CRC, EOF byte
#define MIN_OVERHEAD 11

#if defined(MAX_PAYLOAD)
// for backwards compatibility
#define MIN_MAX_PAYLOAD MAX_PAYLOAD
#endif

#ifdef MIN_MAX_PACKET_SIZE
#if (MIN_MAX_PACKET_SIZE < MIN_OVERHEAD)
#error "MIN_MAX_PACKET_SIZE must be greater than MIN_OVERHEAD"
#endif
// Subtract overhead and max potential stuff bytes
#define MIN_MAX_PAYLOAD (2 * (MIN_MAX_PACKET_SIZE - MIN_OVERHEAD + 1) / 3)
#else
#ifndef MIN_MAX_PAYLOAD
#define MIN_MAX_PAYLOAD 255
#endif
// Add overhead and max potential stuff bytes
#define MIN_MAX_PACKET_SIZE (MIN_MAX_PAYLOAD + MIN_OVERHEAD + (MIN_MAX_PAYLOAD / 2))
#endif

#if (MIN_MAX_PAYLOAD > 255)
#error "MIN frame payloads can be no bigger than 255 bytes"
#endif

// Powers of two for FIFO management. Default is 16 frames in the FIFO, total of 1024 bytes for frame data
Expand All @@ -85,10 +108,6 @@
#define TRANSPORT_FIFO_MAX_FRAMES (1U << TRANSPORT_FIFO_SIZE_FRAMES_BITS)
#define TRANSPORT_FIFO_MAX_FRAME_DATA (1U << TRANSPORT_FIFO_SIZE_FRAME_DATA_BITS)

#if (MAX_PAYLOAD > 255)
#error "MIN frame payloads can be no bigger than 255 bytes"
#endif

// Indices into the frames FIFO are uint8_t and so can't have more than 256 frames in a FIFO
#if (TRANSPORT_FIFO_MAX_FRAMES > 256)
#error "Transport FIFO frames cannot exceed 256"
Expand Down Expand Up @@ -143,7 +162,7 @@ struct min_context {
#ifdef TRANSPORT_PROTOCOL
struct transport_fifo transport_fifo; // T-MIN queue of outgoing frames
#endif
uint8_t rx_frame_payload_buf[MAX_PAYLOAD]; // Payload received so far
uint8_t rx_frame_payload_buf[MIN_MAX_PAYLOAD]; // Payload received so far
uint32_t rx_frame_checksum; // Checksum received over the wire
struct crc32_context rx_checksum; // Calculated checksum for receiving frame
struct crc32_context tx_checksum; // Calculated checksum for sending frame
Expand Down