[coreboot] [RFC] [flashrom] "accelerated" high-level external programmer functions and serial external programmer protocol
c-d.hailfinger.devel.2006 at gmx.net
Fri Jun 5 23:37:22 CEST 2009
On 05.06.2009 23:12, Urja Rannikko wrote:
>> Yes, for that you need flow control. For example, you you have the
>> programmer return the amount of bytes free in the buffer after each
>> command stream you send to the device.
> For a moment i was adding a "return bytes free in buffer" command to
> the protocol, but then i realized that if the code sent that command
> as the last in command stream, and waited for the answer, the answer
> would always be that the buffer is empty, because it just had to go
> though all the data in the buffer to get the command. So i'm sticking
> with the
> - query buffer size in the beginning
> - when doing opbuf writes, count bytes sent
> - if about to have sent too many bytes, instead send NOP and wait for
> the ACK and clear the counter and continue
> I have the protocol specification ready and the AVR code compiles
> already, i'm just moving to flashrom code. I'll attach the .txt to
> this mail, it's better viewed with proper tabs and fixed-width font
> (leafpad fullscreen 1280x1024 is nice :P).
I like the protocol specification. A few minor design notes, though.
> Serial Flasher Protocol Specification
> Command And Answer Sequence - not all commands give an answer
> PC: LENGHT(8bit) COMMAND(8bit) <LENGHT PARAMETER BYTES>
> DEV: ACK/NAK(8bit) <OPTIONAL RETURN BYTES (only if ACK)> or nothing
> ACK = 0xAA
> NAK = 0x55
Since you comunicate over serial, it may happen that one bit is
lost/inserted. Since you specified
ACK = NAK <<1
this could result in spurious acks if there are synchronization
problems. I have seen bitstream sync problems too often with SPI
communication, so I'm extra careful.
ACK = 0x10 (Is Ok)
NAK = 0xBA (BAd)
Your choice, though. Anything else would be just as good if one value is
not a shift of the other.
> All multibyte values are little-endian.
> COMMAND Description Parameters Return Value
> 0x00 NOP none ACK
Maybe call it NOPACK.
> 0x01 Query serial buffer size none ACK + 16bit size / NAK
> 0x02 Query supported bustypes none ACK + 8-bit flags (as per flashrom) / NAK:
> bit 0: PARALLEL
> bit 1: LPC
> bit 2: FWH
> bit 3: SPI if ever supported
> 0x03 Query supported chip size none ACK + 8bit power of two / NAK
> 0x04 Query operation buffer size none ACK + 16bit size / NAK
> 0x05 Read byte 24-bit addr ACK + BYTE / NAK
> 0x06 Read n bytes 24-bit addr + 24-bit lenght ACK + lenght bytes / NAK
lenght -> length
> 0x07 Initialize operation buffer none ACK / NAK
> 0x08 Write to opbuf: Write byte 24-bit addr + 8-bit byte nothing / NAK (NOTE: takes 6 bytes in opbuf)
> 0x09 Write to opbuf: Write byte seq 8-bit byte nothing / NAK (NOTE: takes 1 bytes in opbuf)
Hm. I don't understand the opbuf lengths here.
By the way, having a single-byte write command (like you have) and a
multi-byte write command would probably be a more future-proof design.
0x09 Write to opbuf: Write byte seq 24-bit addr + 24-bit length + n
bytes data ACK/NAK (Note: takes 7+n bytes in opbuf)
> 0x0A Write to opbuf: delay 32-bit usecs nothing / NAK (NOTE: takes 5 bytes in opbuf)
I'd like all commands to send a return code. All those write opcodes
could be returning ACK even before they are sent.
> 0x0B Execute operation buffer none ACK / NAK
> - Execute operation buffer will also clear it
> 0x?? unimplemented command any NAK
0x0C Query programmer interface version 4 bytes "pRoG" ACK + 2
bytes version (>0)
0x0D Query programmer name none ACK + 16 bytes string (NULL
I'd insert interface version and programmer name as 0x00 and 0x01,
moving everything else down. That way, we can change the interface later
and query it easily. The only thing we need to keep constant in the
interface is opcode 0x00. Everything else can be changed as needed.
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