Hi Richard,
Please correct me if I got something wrong:
> Regarding my understanding, that there should be decomposition operations if the
> Max_Read_Request_Size is larger than the Max_Payload_size specified
> by RC port.
I think this means that, for example, a memory read request (a single
short physical TLP packet on PCIe, from the peripheral device to the
CPU) can request more data than Max_Payload_size (128 bytes on i.MX6).
In such case, up to 4 "completion" physical TLP packets are returned by
the CPU (up to 512 bytes, with each individual TLP up to 128 bytes as
per Max_Payload_size).
The device can't request more than 512 bytes, though - the CPU would not
service such request.
> The bit0 of AMBA Multiple Outbound Decomposed NP Sub-Requests Control Register(Offset:0x700 + 0x24)
> had been set to be 1b1 in default.
>
> Note: The description of this bit.
> Enable AMBA Multiple Outbound Decomposed NP Sub- Requests.
> This bit when set to '0' disables the possibility of having multiple outstanding non-posted requests that
> were derived from decomposition of an outbound AMBA request. See Supported AXI Burst Operations for
> more details.
I think the above means that - when I disable the bit in question - I
can't issue memory read requests longer than 128 bytes (max payload
size).
This is not exactly clear to me:
> You should not clear this register unless your application master is
> requesting an amount of read data greater than Max_Read_Request_Size,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Is "completing" such a request at all possible?
The device shouldn't request more data than its (not CPU's)
Max_Read_Request_Size. I. e. if 512 is written to RTL8111's
Max_Read_Request_Size, then the Realtek chip will request max 512 bytes
at a time.
> and the remote device (or switch) is reordering completions that have
> different tags
Fortunately, such completions don't seem to be reordered.
However, I'm not sure how setting a bit in the CPU registers could help
here. I think the only way *IF* the completions were reordered would be
setting MRRS = MPS (= 128 bytes on i.MX6) - so there is nothing that
could be reordered.
--
Krzysztof "Chris" Hałasa
Sieć Badawcza Łukasiewicz
Przemysłowy Instytut Automatyki i Pomiarów PIAP
Al. Jerozolimskie 202, 02-486 Warszawa
