ECALL_TRYSEND, ECALL_TRYRECV

[borancar]

To provide guaranteed streaming delivery in https://github.com/hex-five/multizone-secure-iot-stack, we needed to create mzmsg, examples https://github.com/hex-five/multizone-secure-iot-stack/blob/master/zone1/mzmsg.c and https://github.com/hex-five/multizone-secure-iot-stack/blob/master/zone2/main.c#L171.

mzmsg adds complexity and performance overhead and will need to be reinvented for every case. It would be simpler to provide send and recv methods that return success/failure. This could be used to offer queue sematics. E.g.

• for send

  int ret;
  ret = ECALL_TRYSEND(4, (int[4]){1,2,3,4});
  // ret is SUCCESS
  ret = ECALL_TRYSEND(4, (int[4]){5,6,7,8});
  // ret is FAIL, would overwrite message

• for recv

  int msg[4];
  int ret;
  ret = ECALL_TRYRECV(4, msg);
  // ret is SUCCESS, msg can be anything, even all zeros
  ret = ECALL_TRYRECV(4, msg);
  // ret is FAIL, no messages available

Having these available makes the whole concept of mzmsg redundant and eliminates the need for decoupling queues, saving RAM in the zones.

[cgarlati]

Simpler option: add success return value to existing ECALL_SEND() / ECALL_RECEIVE()

[cgarlati]

Added to multizone-sdk v1.1.0

hexfive-kern a77b8ec4 hexfive-lib 51ee472 hexfive-conf afccb61

Enhanced ECALL_SEND() / ECALL_RECEIVE()

ECALL_SEND() return 1 if the inbox was empty and the message written to the inbox return 0 if the inbox was not empty the message not written to the inbox

ECALL_RECEIVE() return 1 if the inbox was not empty and the message written to memory return 0 if the inbox was empty and the message not written to memory

Note: inbox is not empty when a message was sent but not yet received inbox is empty when no message was sent or the message was sent and received

Note: traps messages are always delivered even if there is an unread message in the inbox ECALL_RECEIVE() no longer clears the inbox with zero values

EXAMPLE (blocking):

Zone1 (producer):

int msg[4]={'T','E','S','T'};

while (!ECALL_SEND(2, msg)) ECALL_WFI();

Zone2 (consumer):

int msg[4]={0,0,0,0};

while (!ECALL_RECEIVE(1, msg)) ECALL_WFI();