[Coco] Fwd: IP packets on my coco

[RETRO Innovations]

On 6/10/2016 12:56 AM, Dave Philipsen wrote:
> To be honest I haven't thoroughly researched or used any of the chips 
> with the exception of the ESP8266.  And , initially, my only 
> preference would be to stay away from the Cirrus chip because it 
> doesn't support interrupts.  I'm not sure if you're understanding 
> though that this CP2200 chip has a multiplexed mode where, as far as I 
> can tell, the maximum amount of I/O space you'll need is two memory 
> locations.  You'll need an 8-bit port through which you can read or 
> write data.  That's one byte.  Then you'll need another port to 
> exercise the ALE signal.  That's another byte.  I assume you're saying 
> that it needs 114 (let's call it 114 instead of 141 because that's 
> what I'm actually reading in the data sheet) bytes of I/O space based 
> upon the fact that it has 114 internal registers.  But let's say you 
> need to read or write to register number 114.  You simply assert the 
> ALE line (also called AS) and put the address value (114) out on the 
> 8-bit port.  Then you release the ALE line and read or write the data 
> in that register (register 114).  So the same 8-bit port that is used 
> to read and write data to the device is also used to select the 
> internal register that you want to read or write.  No need to have a 
> huge I/O space.
True, but I assumed developers would balk at the double abstraction.

The rtl and cs ICs do the same thing, but they do it using the 8 or 16 
registers in the address space.  Specifically:

cs/rtl:

lda #<$cs/rtl memory address
sta CS_RTL_BASE + CS_RTL_ADDRESS_REG_LO
lda #>$cs/rtl memory address
sta CS_RTL_BASE + CS_RTL_ADDRESS_REG_HI
lda #DATA
sta CS_RTL_BASE + CS_RTL_DATA_REG

cp2200:

lda #CP_ADDRESS_REG_LO ; select the Ethernet RAM address low register in 
the window
sta CP_BASE
lda #ALE ; I am assuming here that ALE is a one shot, and we don't need 
to reset it.
sta CP_BASE+1
lda #<cp memory address ; data
sta CP_BASE
lda #DS ; I am assuming here that DS is a one shot (inverted), and we 
don't need to reset it.
sta CP_BASE+1
lda #CP_ADDRESS_REG_HI ; select hi register in the window
sta CP_BASE
lda #ALE ; I am assuming here that ALE is a one shot, and we don't need 
to reset it.
sta CP_BASE+1
lda #>cp memory address ; data
sta CP_BASE
lda #DS ; I am assuming here that DS is a one shot (inverted), and we 
don't need to reset it.
sta CP_BASE+1
lda #CP_DATA_REG ; select data reg
sta CP_BASE
lda #ALE ; I am assuming here that ALE is a one shot, and we don't need 
to reset it.
sta CP_BASE+1
lda #DATA ; data
sta CP_BASE
lda #DS ; I am assuming here that DS is a one shot (inverted), and we 
don't need to reset it.
sta CP_BASE+1



>
> I'm not trying to sway you one way or the other between the rtl or the 
> silicon labs.  They're both probably pretty good chips.  It's just 
> that you should understand what the capabilities of each are in order 
> to make a good decision. 
Fair enough.  I saw the multiplexed bus, but assumed it would introduce 
too much IO cost.
> The Silicon Labs part will require a cheap 3.3v regulator but the I/O 
> is 5v tolerant so no level shifters would be required.
Ah, correct there.  I even saw that, but it did not register.
>   It appears to me that it only requires two bytes of I/O to work if 
> you run it in multiplexed mode.  Look at figure 3 on page 7. There is 
> an 8-bit data bus which the 6809 CPU supplies. There are RD and WR 
> signals which you would multiplex together to be controlled by a R/W 
> line which the CPU supplies.  There's an INT line that goes back to 
> the CPU.  And there's an ALE or address strobe line which is not a 
> signal that would be supplied by the CPU or the cartridge connector.  
> You could use one bit of a simple 8-bit latch to control that line.  
> Total I/O = two bytes.
I concur.
>
> If someone else sees it differently, correct me if I'm wrong.  But 
> that's the way I'm reading the data sheet.
I see it the same way, but I see rtl/cs as having an advantage in this 
space, since they don't need to do double abstraction.

Jim