bus_space(9) - amiga specific questions

[RadosÅaw Kujawa <radoslaw.kujawa%c0ff33.net@localhost>]

Hello.

For a few months, as my time permits, I'm working to deepen my knowledge of the 
NetBSD kernel. Particularly of amiga and amigappc ports. There are still many 
cool devices which are not supported by NetBSD. I'd gladly change this 
situation by writing more drivers, but I feel that my foo is still not strong 
enough. I'd like someone verify my knowledge regarding bus_space on amiga port.

1. Mapping the bus space

Lets assume that hardware has two interesting registers, at 0xdff1f0 and 
0xdff1f4. The registers are 16-bit. I'd write the following code to map it:

#define FOOHW_BASE      0xdff1f0
#define REG0_OFF                0x0
#define REG1_OFF                0x1 /* actually 0x4 but accessed using stride_4 
*/
struct bus_space_tag    foo_bst;
bus_space_tag_t         foo_iot;
bus_space_handle_t      foo_ioh;

foo_bst.base = (u_long) ztwomap(FOOHW_BASE);
foo_bst.absm = &amiga_bus_stride_4; 
foo_iot = &foo_bst;

bus_space_map(foo_iot, 0, 4, 0, foo_ioh);

Is the above code correct? 

Should bus_space_map argument 3 (size) be divided by stride? Or should I 
specify "real" size there?

2. Writing/reading the registers

If I wanted to read 0xdff1f0 and then 0xdff1f4, I'd write:
uint16_t reg0 = bus_space_read_2(foo_iot, foo_ioh, REG0_OFF); 
uint16_t reg1 = bus_space_read_2(foo_iot, foo_ioh, REG1_OFF); 

3. More about strides

The amiga_bus_stride_1 defines bus stride of "1 byte per word". Word means 2 
bytes, right?

Additionally, amiga_bus_stride_2 defines bus stride of 1 byte per 2 words. The 
comment in amiga_bus_simple_2word.c again says "1 byte per word" but I guess 
that is an error and it should be "1 byte per 2 words" ? 

Also, amiga_bus_stride_4 defines bus stride of "1 byte per long", as comment 
states. On an amiga 2 words equals 1 long (32-bit), but amiga_bus_stride_4 is 
defined as a method operating on words, so that would be 1 byte per 4 words? 
I'm really confused, I always thought it's 1 byte per 4 bytes, but now I'm not 
really sure.

4. Misc

What does bus_space_handle_t really contain on amiga? I assume it's a pointer 
to the mapped (virtual) address? Is it normal for it to reside somewhere around 
0x69xxx ?

Can I use physical addresses to read or write data to registers when in DDB?

--
Best regards,
Radoslaw Kujawa