Assembly

Chuck Peddle, the main designer of the 6502, has passed away on Dec. 15th, 2019. Peddle was one of the engineers that developed the 6800 at Motorola. He later went to MOS in order to implement his vision of an 8bit CPU for way less than $300, which was Motorola’s price for the 6800. This idea of a cheap but powerful CPU materialized as the 6501, and finally the 6502. That very chip, which started the microcomputer revolution, and on which both Marko and myself began to write our first code ever at an early age.

Frank van den Hoef, who is adapting the Steckschwein SPI & FAT32 code for his tiny65 machine made me aware of a classic mistake for a 6502 assembly coder to make. Namely in our sdcard driver, when waiting for the “proper” response from the card (which should have bit 7 cleared). The routine handling this looked like this: 1 sd_cmd_response_wait: 2 ldy #sd_cmd_response_retries 3 @l: dey 4 beq sd_block_cmd_timeout ; y already 0?