Blocks

Blocks are the simple mass storage for forth. The mass storage is divided in a series of fixed size memory segments that are transferred at once. To identify a memory segment, a block number is used. This number start with 1 and can be as big as the cell size allows: 65535.

Every block has a fixed size. The ANS94 standard set this size to 1024 bytes, which is rather huge for most atmega’s (only a few would have enough RAM to handle it). The file lib/blocks/blocks.frt has a configurable constant called blocksize which is set to 512. This matches the native block sizes of sd-cards too. That way amforth can address 32Mb mass storage.

There is only one block buffer. The usual block commands are available: block and buffer to load a new block and save a modified block. update to mark the current block as modified. To display the block contents two different list commands are available: one for text data, and one for generic (binary) data (based upon dump). load and thru work too.

> hex 1 list
 0143 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF   ................
 0153 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF   ................
 0163 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF   ................
 0173 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF   ................
 ....
 not modified
> s" .( This is screen #1)" 1 block cmove update
> 1 list
 0143 2E 28 20 54 68 69 73 20 69 73 20 73 63 72 65 65   .( This is scree
 0153 6E 20 23 31 29 FF FF FF FF FF FF FF FF FF FF FF   n #1)...........
 0153 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF   ................
 0163 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF   ................
 0173 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF   ................
 ....
 modified
> flush-buffers \ or load a different block to write back block 1

The Block commands to the buffer management and provide the high level access. The actual read and write process is delegated to 2 deferred words: save-buffer and load-buffer. They get the RAM address of the block buffer and the block number to do the data transfer. They can be changed to talk with various backends. So far the I2C EEPROM Blocks serial EEPROM modules and the built-in flash memory are supported. Other targets such as SD-Cards or SPI memory modules can be added as well.