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Protocol

NRSTI (Negated ReSeT Input) does a hardware reset on BM1397 when signal is Low.

CLKI (CLocK Input) pin must have a 25MHz clock signal, it will be propagated to the CLKO (CLocK Output) pin.

BI (Busy Input) signal must be pulled-down in order to let the BM1397 communicate.

Communication with BM1397 is done by UART on its CI (Ccommand Input) pin and RO (Response Output). Default baudrate is 115200 bps. UART has 8 bits of data, no parity, 1 stop bit (usually represented as 115200 8N1).

Command

command

Preamble

All commands have a fixed 2 byte preamble: 0x55 0xAA

TYPE

  • TYPE = 1: send Job
  • TYPE = 2: send Command

ALL

  • ALL = 0: send to a single Chip
  • ALL = 1: send to all Chips on the Chain

CMD

if TYPE == 1:

  • CMD = 1: send Job

if TYPE == 2:

  • CMD = 0: set Chip Address
  • CMD = 1: write Register
  • CMD = 2: read Register
  • CMD = 3: chain Inactive

Frame Length

Total Frame Length excluding preamble.

Data

Depends on TYPE/CMD, see detailed frames below.

CRC

Can be CRC5 or CRC16 depending on TYPE/CMD, see detailed frames below.

Response

response

All Responses have fixed length : 9 bytes.

Preamble

All commands have a fixed 2 byte preamble: 0xAA 0x55

TYPE

  • TYPE = 0: respond to a command
  • TYPE = 4: respond to a job (nonce)

Data

Depends on TYPE, see detailed frames below.

CRC5

CRC 5 bits with polynomial 0x05, initial value 0x1F, no reflection, no final XOR of the full Frame excluding preamble.

Set Chip Address

On reset, all chips have a logical address of 0. In order to access to a specific chip later, we must give them different addresses.

Warning: Chip Address is different from chip index on the chain. It is a logical concept configurable by software.

To set Chip Address of all chips one by one, we must not send commands to ALL chips, just to the chip with Address = 0, so the first chip on the chain will get the command and not propagate it downward.

The Set Chip Address Command format is:

set_chip_address

No Response is returned by the chip.

Write Register

The Write Register Command format is:

write_register

No Response is returned by the chip.

Read Register

The Read Register Command format is:

read_register

Sending a Read Register Command to ALL chips on the chain is very useful to enumerate them (usually with the Chip Address register), every chip on the chain will send a Response that will be propagated upward.

Register Value

The Register Value Response format is:

register_value

Warning: sometimes a Register Value can be sent spontaneously by a chip (usually the Core Register Value register).

Chain Inactive

The Chain Inactive Command format is:

chain_inactive

No Response is returned by the chip.

Send Job

The Send Job Command format is:

send_job

Nonce

Once hashing, when a nonce is found by a chip on the chain, it is sent on the RO pin (and propagated upward) with this format:

nonce