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Add full explanations for FLOPPY_READ_SECTOR and FLOPPY_WRITE_SECTOR with examples

Ethan Lafrenais 2018-08-30 18:36:30 -04:00
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Hardware:-Floppy-Drive.md

@ -13,10 +13,52 @@ Floppies contains 80 tracks with 18 sectors per track. That's 1440 sectors of 51
### Interrupt Behavior
| Value of A | Action | Energy cost | Result |
| --- | --- | --- | --- |
| `1` | `FLOPPY_POLL` | `0 kJ` | Put the status of the drive (`READY` = `0`, `NO_MEDIA`=`1`) in register `B` |
| `2` | `FLOPPY_READ_SECTOR` | `1 kJ` | Reads sector X to CPU ram starting at address Y |
| `3` | `FLOPPY_WRITE_SECTOR` | `1 kJ` | Writes sector X from CPU ram starting at Y |
| `1` | `FLOPPY_POLL` | `0 kJ` | Puts the status of the drive (`READY` = `0`, `NO_MEDIA`=`1`) in register `B`. |
| `2` | `FLOPPY_READ_SECTOR` | `1 kJ` | Copies a sector from the drive media into CPU RAM ([more info](#floppy_read_sector)). |
| `3` | `FLOPPY_WRITE_SECTOR` | `1 kJ` | Copies 512 words from CPU RAM into a sector on the drive media ([more info](#floppy_write_sector)). |
Read and write operations are synchronous. Track seeking time is 2ms.*
_*Seek time is added to the total execution time, which is not yet calculated as of v1.3a_
#### FLOPPY_READ_SECTOR
Copies a sector from the floppy drive media into CPU RAM. The sector to read is specified by the `X` register. The address in CPU RAM to write the sector to is specified by the `Y` register. If this action is ran without any media in the floppy drive, then CPU RAM will not be changed and register `B` will be set to 0. Otherwise, register `B` will be set to 1 to indicate success.
##### Example sector read
```asm
mov A, 2 ; FLOPPY_READ_SECTOR = 2
mov X, 20 ; Read sector no. 20 from the floppy drive media
; (valid values are 0-1440).
mov Y, 0x2000 ; Write the sector to CPU RAM starting at
; address 0x2000. Addresses 0x2000-0x2200 will
; contain the read sector.
hwi 0x000B ; Floppy Drive hardware ID = 0x000B
; After the hwi instruction completes, register
; B will be set to 1 if the operation was
; successful, otherwise it will be 0.
```
#### FLOPPY_WRITE_SECTOR
Copies 512 words from CPU RAM into a sector on the floppy drive media. The sector to write to is specified by the `X` register. The starting address in CPU RAM to read from is specified by the `Y` register. If this action is ran without any media in the floppy drive, then register `B` will be set to 0. Otherwise, register `B` will be set to 1 to indicate success.
##### Example sector write
```asm
mov A, 3 ; FLOPPY_WRITE_SECTOR = 3
mov X, 12 ; Overwrite sector no. 12 in the floppy drive media
; (valid values are 0-1440).
mov Y, 0x2000 ; Read 512 words from CPU RAM starting at
; address 0x2000. Addresses 0x2000-0x2200 will
; be copied into the sector.
hwi 0x000B ; Floppy Drive hardware ID = 0x000B
; After the hwi instruction completes, register
; B will be set to 1 if the operation was
; successful, otherwise it will be 0.
```