Re: [PATCH v2 30/42] esp: add 4 byte PDMA read and write transfers

[Mark Cave-Ayland]

On 12/02/2021 18:56, Philippe Mathieu-Daudé wrote:

> On 2/9/21 8:30 PM, Mark Cave-Ayland wrote:
> > The MacOS toolbox ROM performs 4 byte reads/writes when transferring data to
> > and from the target. Since the SCSI bus is 16-bits wide, use the memory API
> > to split a 4 byte access into 2 x 2 byte accesses.
> >
> > Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
> > ---
> >   hw/scsi/esp.c | 6 ++++--
> >   1 file changed, 4 insertions(+), 2 deletions(-)
>
> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>
> Out of curiosity, what is the bus used?

AFAICT it's a custom logic chip that sits on the CPU address/data buses that does the 
decoding between the CPU and ESP chip. Other than a simple block diagram of the 
Quadra there isn't much official documentation out there :/

Are you planning to review any more of this series? I'm keen to put out a (hopefully 
final) v3 soon, but I'll hold off for little while if you want more time to look over 
the remaining patches.


ATB,

Mark.