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Detect and report unsupported commands.

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When trying to send an unsupported command, the ostc will simply ignore
the command. Instead of echoing the command byte back, the ostc will
immediately send the ready byte, to indicate it's ready to receive the
next command. We can use this to detect unsupported commands, because
the ready byte is a reserved value and guaranteed to never be a valid
command byte.

Normally we don't send invalid commands. But newer firmware version can
always introduce new commands to support new features. To maintain
backwards compatibility with older firmware versions, it's important to
be able to detect unsupported commands and provide a fallback.
This commit is contained in:
Jef Driesen 2015-03-03 21:33:32 +01:00
parent c7d2bfc9a0
commit bdbe95f221
1 changed files with 14 additions and 7 deletions
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21
src/hw_ostc3.c
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@ -151,6 +151,9 @@ hw_ostc3_transfer (hw_ostc3_device_t *device,
if (device_is_cancelled (abstract))
return DC_STATUS_CANCELLED;
// Get the correct ready byte for the current state.
const unsigned char ready = (device->state == SERVICE ? S_READY : READY);
// Send the command.
unsigned char command[1] = {cmd};
int n = serial_write (device->port, command, sizeof (command));
@ -169,8 +172,13 @@ hw_ostc3_transfer (hw_ostc3_device_t *device,
// Verify the echo.
if (memcmp (echo, command, sizeof (command)) != 0) {
ERROR (abstract->context, "Unexpected echo.");
return DC_STATUS_PROTOCOL;
if (echo[0] == ready) {
ERROR (abstract->context, "Unsupported command.");
return DC_STATUS_UNSUPPORTED;
} else {
ERROR (abstract->context, "Unexpected echo.");
return DC_STATUS_PROTOCOL;
}
}
if (input) {
@ -216,16 +224,15 @@ hw_ostc3_transfer (hw_ostc3_device_t *device,
if (cmd != EXIT) {
// Read the ready byte.
unsigned char ready[1] = {0};
unsigned char expected = (device->state == SERVICE ? S_READY : READY);
n = serial_read (device->port, ready, sizeof (ready));
if (n != sizeof (ready)) {
unsigned char answer[1] = {0};
n = serial_read (device->port, answer, sizeof (answer));
if (n != sizeof (answer)) {
ERROR (abstract->context, "Failed to receive the ready byte.");
return EXITCODE (n);
}
// Verify the ready byte.
if (ready[0] != expected) {
if (answer[0] != ready) {
ERROR (abstract->context, "Unexpected ready byte.");
return DC_STATUS_PROTOCOL;
}