jcsbanks

MUT command - switch to DMA mode - no reply from ECU, PC to give brief delay before sending first DMA packet...
DMA RECEIVE to ECU RAM BUFFER setup, SET RECEIVE ENABLE on serial port 0
DMA BLOCK SENT FROM PC TO ECU - 4 BYTES TO RAM BUFFER
Address 2 bytes
Length 13 bits
FFFFxxxx or 0000xxxx base 1 bit
Indirect or direct 1 bit
Transmit or receive 1 bit
Interrupt when DMA finished so that ECU sets up SECOND DMA TRANSFER, CLEAR RECEIVE ENABLE IF IT IS A TRANSMIT TO PREVENT ECU RECEIVING ALL THE ECHOES (tied Tx and Rx with K-line on OBD port!), ENABLE TXI if TRANSMIT
Data block Length bytes
Interrupt when DMA finished to that we return to line 2, but not until TEND

In DMA mode ECU must reset keep alive timers

Result: 1562 items logged per second at standard baud rate, fuel or timing maps read/written in less than 0.25 seconds? No performance hit to the ECU as a fraction of a percent of cycles will be stolen in DMA cycle steal mode.

Comments from those who have read the SH7052/7055 hardware manual please.